Application of Recycled Materials in Highway Projects
FINAL REPORT
PRINCIPAL INVESTIGATOR:
Phillip S.K. Ooi, Ph.D., P.E.
Associate Professor
PREPARED IN COOPERATION WITH:
State of Hawaii, Department of Transportation, Materials and Testing Branch and
U.S. Department of Transportation, Federal Highway Administration
Honolulu, Hawaii
December 17, 2010
HWY-L-2005-04
December 17, 2010
Application of Recycled Materials in Highway Projects
P.S.K. Ooi, A.R. Archilla, Y. Song & M.L.Q. Sagario
Department of Civil & Environmental Engineering
University of Hawaii at Manoa
2540 Dole St., Holmes Hall 383
Honolulu, HI 96822
FINAL
2/1/06 to 8/31/10
Hawaii Department of Transportation
Highways Division
869 Punchbowl St., Honolulu, HI 96813
Prepared in cooperation with the U.S. Department of Transportation and
Federal Highway Administration
The impetus and pressure for pavement and geotechnical engineers to incorporate
sustainability in engineering projects has led to a rise in the reuse of materials such as
recycled concrete aggregate (RCA), reclaimed asphalt pavement (RAP) and recycled glass (RG) as
fill and in pavement sub-layers.
Consequently, an understanding of their behavior and
characteristics are necessary prior to use in practice.
Tests to characterize the materials, to assess their compactability and to address the
vulnerability of RCA to tufa formation and aluminum corrosion were performed.
It was found
that RCA from a mechanical viewpoint has superior strength and stiffness.
However, when
exposed to water, it has a tendency to hydrate. Initially, the hydration leads to a gain in
strength and stiffness.
Subsequently, the material is prone to shrinkage cracking.
Nevertheless, the RCA stiffness and strength are still quite appreciable compared to the precracked value.
RCA made with Hawaiian basaltic aggregate was found to not produce tufa in
significant quantities as compared to dolomitic-based RCA when subjected to an accelerated
leaching experiment. However, corrosion of aluminum in the presence of RCA was found to cause
significant swell pressures and as such, RCA should not be used in close proximity with any
aluminum infrastructure or should not be contaminated with aluminum. RAP on the other hand is
more inert.
However, the mechanical properties are less desirable than those of virgin
aggregate and RCA.
While the resilient modulus of RAP is quite appreciable, it suffered
significant permanent deformation or rutting and its use should be contained by limiting its
percent content.
The RG obtained in this study was crushed to a very fine gradation.
The
large quantities of fines make working with RG hazardous as it can cause skin irritation.
Finally, changes to the State of Hawaii Standard Specifications are proposed to
incorporate the use of these three recycled materials as a fill or as an unbound layer in
pavements. Two new sections (for RAP and RCA) are also proposed as additions to the current
standard specifications.
Reclaimed Asphalt Pavement, Recycled
Concrete Aggregate, Recycled Glass,
Tufa, Corrosion of Aluminum, Resilient
Modulus, Permanent Deformation
Unclassified
Document is available to the U.S. public through the
National Technical Information Service, Springfield, VA
22161
Unclassified
390
ACKNOWLEDGEMENTS AND DISCLAIMER
The authors are grateful for the funding and support provided by the Hawaii
Department of Transportation (HDOT) and the Federal Highway Administration
(FHWA).
The authors greatly appreciate the many insightful contributions provided by:
Herbert Chu (HDOT)
Brandon Hee (HDOT)
Eric Hellebrand (University of Hawaii, Department of Geology and
Geophysics)
David Muenow (University of Hawaii, Department of Chemistry)
Farshad Rajabipour (Pennsylvania State University, Department of Civil
and Environmental Engineering)
The authors are also grateful to the following individuals and organizations for
providing assistance gratis to the project:
●
●
●
●
Richard Levins of Grace Pacific Corp. for providing the recycled materials and
virgin aggregate for testing
Jane Schoonmaker of the Department of Oceanography at the University of
Hawaii for performing X-ray diffraction
Karl Seff of the Department of Chemistry for providing input on the X-ray
diffraction results
Shiv Sharma of Hawaii Institute of Geophysics and Planetology at the University
of Hawaii for performing Raman spectroscopy
The contributions of former graduate research assistants Dr. Yonghui Song, Michelle
Sagario, Partheeban Selvarajah and Michael Skowronek, whose dissertation and
theses form a great part of this research report. The authors also acknowledge
Seungdon Joo for performing the swell pressure tests and numerical analysis in
Chapter 5 and former undergraduate research assistant Melanie Li for performing tests
on recycled glass.
THE CONTENTS OF THIS REPORT REFLECT THE VIEW OF THE AUTHORS, WHO ARE RESPONSIBLE FOR
THE FACTS AND ACCURACY OF THE DATA PRESENTED HEREIN.
THE CONTENTS DO NOT
NECESSARILY REFLECT THE OFFICIAL VIEWS OR POLICIES OF THE STATE OF HAWAII, DEPARTMENT
OF TRANSPORTATION OR THE FEDERAL HIGHWAY ADMINISTRATION. THIS REPORT DOES NOT
CONSTITUTE A STANDARD, SPECIFICATION OR REGULATION.
TABLE OF CONTENTS
ACKNOWLEDGEMENTS AND DISCLAIMER .................................................................... I
TABLE OF CONTENTS .......................................................................................................... II
LIST OF TABLES .................................................................................................................... VI
LIST OF FIGURES ............................................................................................................... VIII
CHAPTER 1 INTRODUCTION ............................................................................................... 1
1.1 RG ....................................................................................................................................... 1
1.1.1 Uses of RG ................................................................................................................... 2
1.1.2 Challenges of Using RG............................................................................................... 2
1.1.3 Properties ..................................................................................................................... 3
1.2 RAP ..................................................................................................................................... 4
1.2.1 Uses of RAP ................................................................................................................. 5
1.2.2 Challenges of Using RAP............................................................................................. 5
1.2.3 Properties ..................................................................................................................... 5
1.3 RCA..................................................................................................................................... 5
1.3.1 Uses of RCA ................................................................................................................. 6
1.3.2 Challenges of Using RCA ............................................................................................ 6
1.3.3 Properties ..................................................................................................................... 7
1.4 OBJECTIVES ......................................................................................................................... 7
1.5 ORGANIZATION OF REPORT .................................................................................................. 8
CHAPTER 2 MATERIAL CHARACTERIZATION ........................................................... 10
2.1 MATERIAL SOURCE ..................................................................................................... 10
2.2 GRAIN SIZE DISTRIBUTION ........................................................................................ 11
2.3 SPECIFIC GRAVITY AND ABSORPTION ................................................................... 15
2.4 LA ABRASION ................................................................................................................ 16
2.5 COARSE AGGREGATE VOID CONTENT ................................................................... 17
2.6 SAND EQUIVALENT TEST ........................................................................................... 18
2.7 ATTERBERG LIMITS ..................................................................................................... 19
2.8 ASPHALT CONTENT OF RAP ....................................................................................... 19
2.9 CALIFORNIA BEARING RATIO ................................................................................... 20
2.9.1 OVERVIEW OF THE CBR TEST .............................................................................. 20
2.9.1.1 Compaction ......................................................................................................... 21
2.9.1.2 Soaking ............................................................................................................... 22
2.9.1.3 CBR Testing........................................................................................................ 23
2.9.2 CBR TEST SAMPLE GRADATION AND RESULTS ................................................. 25
2.9.2.1 Sample Gradation................................................................................................ 25
2.9.2.2 CBR..................................................................................................................... 26
2.9.2.3 Changes in Gradation after Compaction and CBR testing ................................. 28
2.9.3 CBR OF BLENDS ...................................................................................................... 32
2.9.4 EFFECTS OF GRADATION ON CBR OF RCA AND RAP ...................................... 37
ii
2.9.5 CBR SUMMARY AND CONCLUSIONS ................................................................... 41
2.10 RESILIENT MODULUS ................................................................................................ 44
2.10.1 LITERATURE REVIEW ........................................................................................... 44
2.10.1.1 Use of Mr in Pavement Design ......................................................................... 44
2.10.1.2 Factors Influencing Mr of Unbound Granular Material .................................... 47
2.10.1.3 Mr Test Procedures ........................................................................................... 48
2.10.1.4 Mr Models ......................................................................................................... 49
2.10.1.5 Recent Studies on Mr of RCA and RAP ........................................................... 52
2.10.2 CHARACTERISTICS OF MATERIALS, TEST EQUIPMENT AND PROCEDURES
............................................................................................................................................. 54
2.10.2.1 Gradation and Compaction Curves ................................................................... 54
2.10.2.2 Sample Preparation ........................................................................................... 60
2.10.2.3 Mr Test Procedure and Equipment .................................................................... 63
2.10.3 FACTORS AFFECTING Mr .................................................................................... 67
2.10.3.1 Effect of Stress Level on Mr ............................................................................. 67
2.10.3.2 Effect of Water Content on Mr.......................................................................... 68
2.10.3.3 Effect of Dry Density on Mr ............................................................................. 70
2.10.4 Mr MODELING ....................................................................................................... 71
2.10.4.1 Mr Modeling of Individual Samples ................................................................. 72
2.10.4.2 Two-Parameter Mr Modeling for Each Material Dataset ................................. 76
2.10.4.3 Three-Parameter Mr Modeling for Each Material Dataset ............................... 83
2.10.5 SUMMARY AND CONCLUSIONS .......................................................................... 87
2.11 PERMANENT DEFORMATION TEST AND SHAKEDOWN ANALYSIS ............... 89
2.11.1 LITERATURE REVIEW ........................................................................................... 89
2.11.1.1 Consideration of PD of UGM in Pavement Design .......................................... 93
2.11.1.1.1 Behavior of UGM in a PD Test ................................................................. 99
2.11.1.1.2 Consideration of PD in Pavement Design ............................................... 101
2.11.1.2 Shakedown Theory ......................................................................................... 102
2.11.1.3 Factors affecting PD of UGM ......................................................................... 106
2.11.1.4 Permanent Deformation Models ..................................................................... 107
2.11.2 SELECTION OF CONFINING STRESS................................................................ 112
2.11.3 SELECTION OF DEVIATOR STRESSES FOR PD TESTING .............................. 112
2.11.4 PD TEST RESULTS ............................................................................................... 116
2.11.4.1 Target Sample Water Content and Dry Density ............................................. 116
2.11.4.2 Behavioral Ranges from Single-Stage PD Tests ............................................ 118
2.11.4.3 Models for Single-Stage PD Tests .................................................................. 128
2.11.4.4 Multi-Stage PD Tests ...................................................................................... 138
2.11.4.5 Multi-Stage PD Test Results and Analysis ..................................................... 139
2.11.5 SUMMARY AND CONCLUSIONS ........................................................................ 144
CHAPTER 3 ASSESSING THE COMPACTABILITY OF RECYCLED CONCRETE
AGGREGATE AND RECLAIMED ASPHALT PAVEMENT ......................................... 148
3.1 BACKGROUND AND OBJECTIVES ...................................................................................... 148
3.1.1 Nuclear Gauge ......................................................................................................... 148
3.1.2 Time Domain Reflectometry .................................................................................... 150
3.1.3 GeoGauge ................................................................................................................ 151
3.1.4 Portable Falling Weight Deflectometer (PFWD) .................................................... 152
iii
3.1.5 FlexiForce® Electrical Sensors .............................................................................. 153
3.1.6 Objectives ................................................................................................................. 154
3.2 EXPERIMENTAL SET-UP ............................................................................................ 155
3.2.1 Materials .................................................................................................................. 155
3.2.1.1 Gradation........................................................................................................... 156
3.2.1.2 Classification..................................................................................................... 156
3.2.1.3 Compaction Curve ............................................................................................ 157
3.2.1.4 Friction Angle ................................................................................................... 159
3.2.2 Calibration of Instruments ....................................................................................... 160
3.2.3 Bin Set-up and Compaction ..................................................................................... 161
3.2.4 Post-compaction Measurements .............................................................................. 166
3.3 DENSITY EVALUATION USING NUCLEAR GAUGE AND TIME DOMAIN
REFLECTOMETRY ............................................................................................................ 167
3.3.1 Introduction.............................................................................................................. 167
3.3.1.1 Previous Studies on the Nuclear Gauge on RCA and RAP .............................. 167
3.3.1.2 Previous Studies on Time Domain Reflectometry............................................ 167
3.3.2 Test Results .............................................................................................................. 180
3.3.2.1 Actual Dry Density ........................................................................................... 180
3.3.2.2 Measured Moisture Content .............................................................................. 182
3.3.2.3 Measured Dry Density ...................................................................................... 184
3.3.2.4 Post-Compaction Moisture Content and Density ............................................. 186
3.3.3. Summary and Conclusions...................................................................................... 190
3.4 STIFFNESS EVALUATION USING PORTABLE FALLING WEIGHT
DEFLECTOMETER AND GEOGAUGE ............................................................................ 194
3.4.1 Introduction.............................................................................................................. 194
3.4.2 Literature Review ..................................................................................................... 195
3.4.3 Quality Control ........................................................................................................ 204
3.4.4 Test Results .............................................................................................................. 205
3.4.4.1 Elastic Modulus During Compaction................................................................ 205
3.4.4.2 Post Compaction Measurements ....................................................................... 209
3.4.4.3 Correlation Between PFWD and GeoGauge Stiffness ..................................... 211
3.4.5 Summary and Conclusions....................................................................................... 212
3.5 EARTH PRESSURES ........................................................................................................... 214
3.5.1 Introduction.............................................................................................................. 214
3.5.2 Literature Review ..................................................................................................... 215
3.5.2.1 Rankine Active and Passive Lateral Earth Pressure Coefficients ..................... 215
3.5.2.2 Stresses in Silos................................................................................................. 216
3.5.3 Sensors ..................................................................................................................... 218
3.5.3.1 Calibration......................................................................................................... 219
3.5.3.2 Set Up................................................................................................................ 219
3.5.4 Test Results .............................................................................................................. 220
3.5.4.1 Dial Gauge Readings ........................................................................................ 220
3.5.4.2 Interface Friction Angle .................................................................................... 220
3.5.4.3 Depth vs. Vertical Stress ................................................................................... 221
3.5.4.4 Depth vs. Lateral Pressure ................................................................................ 222
3.5.5 Summary and Conclusions....................................................................................... 224
iv
CHAPTER 4 POTENTIAL FOR TUFA PRECIPITATION WITH CRUSHED
CONCRETE CONTAINING COARSE BASALTIC AND FINE CORALLINE SAND
AGGREGATES ...................................................................................................................... 225
4.1 INTRODUCTION........................................................................................................... 225
4.2 LITERATURE REVIEW ................................................................................................ 226
4.3 CHEMISTRY OF TUFA ................................................................................................ 228
4.4 CHARACTERIZATION OF THE AS-RECEIVED RCA.............................................................. 229
4.4.1 Petrographic Description of the RCA ...................................................................... 229
4.4.2 Elemental Composition of the RCA ......................................................................... 230
4.5 LEACHING EXPERIMENT .......................................................................................... 231
4.6 DISCUSSION OF TEST RESULTS ............................................................................... 234
4.6.1 pH of the Leachate ................................................................................................... 234
4.6.2 ICP-AES Tests on Leachate ..................................................................................... 236
4.6.3 Characterization of the RCA Aggregate before and after Leaching Experiment .... 241
4.6.4 XRD Test Results...................................................................................................... 242
4.6.5 SEM with EDS Test Results ..................................................................................... 244
4.6.6 Sample Observation after Leaching Experiment ..................................................... 248
4.7 SUMMARY AND CONCLUSIONS .............................................................................. 250
CHAPTER 5 FORENSIC INVESTIGATION OF A DISTRESSED PAVEMENT
SUPPORTED ON A BASE COURSE CONTAINING RECYCLED CONCRETE
AGGREGATE......................................................................................................................... 253
5.1 INTRODUCTION................................................................................................................. 253
5.2 PROJECT DESCRIPTION AND OBJECTIVES ........................................................... 254
5.3 BACKGROUND............................................................................................................. 256
5.4 EXPERIMENTAL INVESTIGATIONS ........................................................................ 259
5.4.1 Identification of the Field Reaction Product ........................................................... 259
5.4.1.1 SEM with EDS.................................................................................................. 259
5.4.1.2 XRD .................................................................................................................. 262
5.4.1.3 Raman Spectroscopy......................................................................................... 265
5.4.2 Laboratory Simulation of Field Reaction ............................................................... 267
5.4.3 Swell Pressure Test .................................................................................................. 270
5.5 NUMERICAL ANALYSIS ............................................................................................ 272
5.6 SUMMARY AND CONCLUSIONS ................................................................................... 276
CHAPTER 6 IMPLICATIONS OF RESEARCH RESULTS ON SPECIFICATIONS .. 278
REFERENCES ........................................................................................................................ 287
APPENDIX .............................................................................................................................. 314
v
LIST OF TABLES
Table 2-1 Specific gravity and absorption
16
Table 2-2 LA abrasion test results of four materials
17
Table 2-3 Void content of coarse aggregate of each material
18
Table 2-4 Sand equivalent (SE) test results
19
Table 2-5 Standard load for high quality crushed stone material
21
Table 2-6 Summary of available Mr models
51
Table 2-7 Mr studies on RCA and RAP
53
Table 2-8 Water contents and dry densities of Mr test samples
59
Table 2-9 Summary of regression parameters for Equations 2.2 and 2.3
73
Table 2-10 Summary of descriptive statistics for k1 and k2 in Equation 2.2
74
Table 2-11 Summary of descriptive statistics for k1, k2 and k3 in Equation 2.3
75
Table 2-12 Sample calculation of Szav - S and e - ezav for VA.
77
Table 2-13 Regression results for VA using equations 4.2 and 4.4
78
Table 2-14 Summary of parameter estimates, t-statistics and R2 for two-parameter Mr model
using equations 2.2 and 2.4
80
Table 2-15 Summary of regression constants of RCA and VA blends using equations 2.2 and
2.5
82
Table 2-16 Summary of regression constants of RAP and VA blends using equations 2.2 and
2.5
82
Table 2-17 Regression results for VA using Equations 2.3 and 2.6
83
2
Table 2-18 Summary of parameter estimates, t-statistics and R for three-parameter Mr model
using equations 2.3 and 2.6
85
Table 2-19 Summary of regression constants for RCA and VA blends using equations 2.3 and
2.7
86
Table 2-20 Summary of regression results for RAP and VA blends using equations 2.3 and 2.7
87
Table 2-21 Recent PD studies on RCA and RAP
91
Table 2-22 Methods for distinguishing the various PD behavioral ranges
106
Table 2-23 Models for estimating permanent strain as a function of the number of load cycles
(modified after Hornych and El Abd, 2004)
107
Table 2-24 Models for estimating permanent strain as a function of the applied stress level
(modified after Hornych and El Abd, 2004)
108
Table 2-25 Models for estimating permanent strain as a function of the number of load cycles
and applied stress level
109
Table 2-26 Single-stage PD test matrix and shear test results
114
Table 2-27 Multi-stage PD test load sequence for RCA&VA
115
Table 2-28 Water content and dry density for single-stage PD tests
117
Table 2-29 Behavioral ranges based on a single-stage PD testing
126
Table 2-30 Power law model parameters for all materials tested
129
Table 2-31 Summary of regression constants for the Huurman model
131
Table 2-32 Parameter estimates and t-statistics for VA using the Huurman model
132
Table 2-33 Summary of regression constants for the first term of the Huurman model
132
vi
Table 2-34 Parameter estimates and t-statistics for the first term of the Huurman model for VA
133
Table 2-35 Summary of regression constants for the first term of the modified Huurman model
135
Table 2-36 Parameter estimates and t-statistics for the first term of the modified Huurman
model for VA
135
Table 2-37 Summary of the bias (slope) and coefficient of determination for the models
evaluated
137
Table 2-38 Summary of stress ratios at different permanent strains in multi-stage permanent
deformation tests.
140
Table 2-39 Behavioral ranges based on a single- and multi-stage PD testing.
143
Table 3-1 Experiment timeline
166
Table 3-2 Summary of TDR calibration constants
177
Table 3-3 Soil specific calibration constants for this study
177
Table 3-4 Moisture content summary
182
Table 3-5 Dry density summary
185
Table 3-6 Summary of zone of influence from the literature
204
Table 3-7 RAP stiffness for each lift
208
Table 3-8 RCA stiffness for each lift
208
Table 3-9 Variation of RAP stiffness with time
211
Table 3-10 Variation of RCA stiffness with time
211
Table 4-1 X-ray fluorescence test results on the as-received RCA showing the major elements
reported in terms of weight of oxides in percent
231
Table 4-2 Aggregate used in leaching tests and test objectives
233
Table 4-3 Summary of ICP-AES results on the film collected from the walls of two test
chambers
250
Table 5.1 Possible deterioration of RCA and their reaction products.
258
Table 5.2 Average elemental composition of the reaction product from EDS analysis.
260
Table 5.3 Summary of material properties used in the numerical analysis.
273
Table 6-1 Test results for “loose” and “dense” 100%RCA sheared immediately after
consolidation (after Selvarajah, 2010)
279
Table 6-2 Test results for “loose” and “dense” as-received 100%RG in direct shear (Ooi et al.,
2008)
283
Table 6-3 Summary of maximum allowable recycled materials as a percent by dry weight of the
total composite aggregate weight for various highway applications
285
vii
LIST OF FIGURES
Figure 2-1 Comparison of grain size distribution of recycled materials with HDOT’s 2.5-inch
maximum nominal untreated base course requirements ..................................................... 12
Figure 2-2 Comparison of grain size distribution of recycled materials with HDOT’s 1.5-inch
maximum nominal untreated base course requirements ..................................................... 12
Figure 2-3 Comparison of grain size distribution of recycled materials with HDOT’s 0.75-inch
maximum nominal untreated base course requirements ..................................................... 13
Figure 2-4 Comparison of grain size distribution of recycled materials with HDOT’s top 6-inch
subbase requirements .......................................................................................................... 13
Figure 2-5 Comparison of grain size distribution of recycled materials with HDOT’s
requirements for subbase below top 6 inches ..................................................................... 14
Figure 2-6 Comparison of grain size distribution of recycled materials with HDOT’s
embankment fill requirements ............................................................................................ 14
Figure 2-7 Comparison curves of VA with HDOT’s 1.5-inch maximum nominal untreated base
course requirements ............................................................................................................ 15
Figure 2-8 Penetration portion of CBR test (Porter 1949) .......................................................... 22
Figure 2-9 CBR test set up .......................................................................................................... 23
Figure 2-10 CBR test gradation for VA, RCA, RAP and their blends with respect to HDOT
gradations (upper bound) for fill, subbase and base course ................................................ 25
Figure 2-11 CBR test gradation for RG & VA blends................................................................ 26
Figure 2-12 CBR test results (a) Dry unit weight versus water content and (b) CBR versus water
content ................................................................................................................................. 27
Figure 2-13a Variation of gradation before and after compaction and CBR test - VA .............. 30
Figure 2-13b Variation of gradation before and after compaction and CBR test - RCA ........... 30
Figure 2-13c Variation of gradation before and after compaction and CBR test - RAP ............ 31
Figure 2-13d Variation of gradation before and after compaction and CBR test - RG .............. 31
Figure 2-14a Dry unit weight versus water content for RCA blends ......................................... 33
Figure 2-14b CBR versus water content for RCA blends........................................................... 33
Figure 2-15a Dry unit weight versus water content for RAP blends .......................................... 34
Figure 2-15b CBR versus water content for RAP blends ........................................................... 34
Figure 2-16a Dry unit weight versus water content for RG blends ............................................ 35
Figure 2-16b CBR versus water content for RG blends ............................................................. 35
Figure 2-17 Gradations for CBR Test ......................................................................................... 37
Figure 2-18a Effect of gradation on RCA compaction curve ..................................................... 39
Figure 2-18b Effect of gradation on RCA CBR strength ........................................................... 39
Figure 2-19a Effect of gradation on RAP compaction curve ..................................................... 40
Figure 2-19b Effect of gradation on RAP CBR strength ............................................................ 40
Figure 2-20 Problems related to laboratory Mr test (Puppala 2008) ........................................... 46
Figure 2-21 Types of correlations used for predicting Mr by the various state DOTs (Puppala
2008) ................................................................................................................................... 47
Figure 2-22 Sample gradation used for Mr test ........................................................................... 55
Figure 2-23a Compaction curve for VA (Gs = 2.85 for ZAV curve) ......................................... 56
Figure 2-23b Compaction curve for RCA (Gs = 2.85 for ZAV curve) ....................................... 56
viii
Figure 2-23c Compaction curve for RCA&VA (Gs = 2.85 for ZAV curve) .............................. 57
Figure 2-23d Compaction curve for RAP (Gs = 2.64 for ZAV curve) ....................................... 57
Figure 2-23e Compaction curve for RAP&VA (Gs = 2.74 for ZAV curve)............................... 58
Figure 2-23f Compaction curve for RG&VA (Gs = 2.74 for ZAV curve) ................................. 58
Figure 2-24 Materials tested: RAP after Mr testing (top left), RG and VA blend after Mr testing
(top right), 100% RCA before (bottom left) and after (bottom right) mixing with water but
before Mr testing. ................................................................................................................ 62
Figure 2-25 Sample preparation apparatus (left) and compaction density control (right) .......... 62
Figure 2-26 Sample ready for testing (left) and the LVDT setup (right) .................................... 65
Figure 2-27 Computer-controlled data acquisition system ......................................................... 65
Figure 2-28 Sample after Mr and quick shear testing ................................................................. 66
Figure 2-29a Mr as a function of stress level - VA (Legend - confining stress) ......................... 69
Figure 2-29b Mr as a function of stress level - RG&VA (Legend - confining stress) ................ 69
Figure 2-30 Effect of water content on Mr for VA (Legend - molding water content/dry density)
............................................................................................................................................. 70
Figure 2-31 Effect of dry density on Mr for VA (Legend - molding water content/dry density) 71
Figure 2-32 Szav - S is related to x and e - ezav is related to y...................................................... 77
Figure 2-33 Measured and predicted Mr for VA using equations 2.2 and 2.4 ............................ 78
Figure 2-34 Measured and predicted Mr for VA using equations 4.3 and 4.6 ............................ 84
Figure 2-35 Schematic illustration of shear stress ratio criterion in pavement design (Tutumluer
and Dawson, 2004) ............................................................................................................. 93
Figure 2-36 Attenuation of traffic induced stresses with depth (Christopher et al., 2006)......... 94
Figure 2-37 Stresses beneath rolling wheel load (Lekarp et al., 2000)....................................... 96
Figure 2-38 Field stresses during a load-unload-reload path (redrawn after Mayne and
Kulhawy, 1982)................................................................................................................... 97
Figure 2-39 Hysteresis loop during a load-unload cycle in a RLT test on UGM ....................... 99
Figure 2-40 Shakedown ranges (Tutumluer and Dawson, 2004) ............................................. 103
Figure 2-41 Shakedown behavior for UGM (Werkmeister, 2003) ........................................... 104
Figure 2-42 PD ranges by permanent strain rate (Werkmeister et al., 2004) ........................... 105
Figure 2-43 PD ranges by resilient strain (Werkmeister et al., 2004) ...................................... 105
Figure 2-44a Permanent strain versus N at different deviator stress levels for VA ................. 118
Figure 2-44b Resilient moduli versus N at different deviator stress levels for VA .................. 119
Figure 2-44c Permanent strain rate versus permanent strain at different deviator stress levels for
VA ..................................................................................................................................... 119
Figure 2-45a Permanent strain versus N at different deviator stress levels for RCA ............... 120
Figure 2-45b Resilient moduli versus N at different deviator stress levels for RCA ............... 120
Figure 2-45c Permanent strain rate versus permanent strain at different deviator stress levels for
RCA .................................................................................................................................. 121
Figure 2-46a Permanent strain versus N at different deviator stress levels for RCA&VA ...... 121
Figure 2-46b Resilient moduli versus N at different deviator stress levels for RCA&VA ...... 122
Figure 2-46c Permanent strain rate versus permanent strain at different deviator stress levels for
RCA&VA ......................................................................................................................... 122
Figure 2-47a Permanent strain versus N at different deviator stress levels for RAP ............... 123
Figure 2-47b Resilient moduli versus N at different deviator stress levels for RAP ................ 123
Figure 2-47c Permanent strain rate versus permanent strain at different deviator stress levels for
RAP ................................................................................................................................... 124
ix
Figure 2-48a Permanent strain versus N at different deviator stress levels for RAP&VA ....... 124
Figure 2-48b Resilient moduli versus N at different deviator stress levels for RAP&VA ....... 125
Figure 2-48c Permanent strain rate versus permanent strain at different deviator stress levels for
RAP&VA .......................................................................................................................... 125
Figure 2-49a Power law model parameters A versus deviator stress level for VA .................. 130
Figure 2-49b Power law model parameters B versus deviator stress level for VA .................. 130
Figure 2-50a Predicted versus measured PD using first term of the Huurman model ............. 134
Figure 2-50b Predicted versus measured PD using first term of the Huurman model ............. 134
Figure 2-51a Predicted versus measured PD using the first term of the modified Huurman
model................................................................................................................................. 136
Figure 2-51b Predicted versus measured PD using the first term of the modified Huurman
model................................................................................................................................. 136
Figure 2-52 Multi-stage permanent deformation test results for recycled concrete aggregate
(RCA): (a) Permanent strain versus number of cycles and (b) Resilient modulus/strain
versus number of cycles. Deviator stresses are notated in figure. ................................... 142
Figure 3-1 Troxler nuclear moisture/density gauge model 3450 used in the experiments ....... 150
Figure 3-2 Time Domain Reflectometry test set-up (a) round coaxial head connected to the
TDR gauge which is operated using a PDA and (b) multi-rod probes below the coaxial
head ................................................................................................................................... 151
Figure 3-3 GeoGauge device .................................................................................................... 152
Figure 3-4 Portable falling weight deflectometer ..................................................................... 153
Figure 3-5 FlexiForce® sensor ................................................................................................. 154
Figure 3-6 Comparison of grain size distribution of RAP and RCA with HDOT specification
requirements for 0.75-inch ................................................................................................ 157
Figure 3-7 RAP compaction curve ........................................................................................... 158
Figure 3-8 RCA compaction curve ........................................................................................... 158
Figure 3-9 Sensors attached to bin (Left) and sensors connected to transmitters (Right) ........ 161
Figure 3-10 Profile view of bin ................................................................................................. 162
Figure 3-11 Electric concrete mixer used to blend RAP with water and RCA with water ...... 163
Figure 3-12 Bosch hammer with tamper plate and wood base ................................................. 164
Figure 3-13 Plan view of test locations in bin .......................................................................... 164
Figure 3-14 Dial gauges ............................................................................................................ 165
Figure 3-15 Parameters to determine Ka (Durham Geo Slope Indicator, 2003) ....................... 169
Figure 3-16 Parameters to determine ECb (Yu and Drnevich, 2004) ....................................... 170
Figure 3-17 Center rod guide and non-conductive base (Left) and coaxial head and mold collar
on compaction mold (Right) ............................................................................................. 172
Figure 3-18 Constants a and b for (a) RAP and (b) RCA ......................................................... 173
Figure 3-19 Constants c and d for (a) RAP and (b) RCA ......................................................... 174
Figure 3-20 Constants f and g for (a) RAP and (b) RCA ......................................................... 176
Figure 3-21 Template (Right) and probes inserted in RAP (Left) ............................................ 179
Figure 3-22 Deflection profile based on dial gauge readings ................................................... 181
Figure 3-23 RAP moisture content comparison........................................................................ 183
Figure 3-24 RCA moisture content comparison ....................................................................... 183
Figure 3-25 RAP dry density comparison ................................................................................ 184
Figure 3-26 RCA dry density comparison ................................................................................ 185
Figure 3-27 RAP moisture content versus time ........................................................................ 186
x
Figure 3-28 RCA moisture content versus time ....................................................................... 187
Figure 3-29 Bin covered with lid .............................................................................................. 188
Figure 3-30 RAP dry density versus time ................................................................................. 189
Figure 3-31 RCA dry density versus time ................................................................................ 190
Figure 3-32 PFWD release trigger (Left) and drop weight, rubber buffers, velocity transducer
(Right) ............................................................................................................................... 196
Figure 3-33 High quality PFWD reading (Fleming et al., 2009) .............................................. 198
Figure 3-34 High rebound PFWD reading (Fleming et al., 2009) ............................................ 198
Figure 3-35 Effect of subsequent PFWD drops (Fleming et al., 2009) .................................... 199
Figure 3-36 RCA PFWD test quality assessment ..................................................................... 200
Figure 3-37 Schematic of GeoGauge (GeoGauge User Guide, 2007)...................................... 201
Figure 3-38 RAP stiffness, dry density and moisture content versus height ............................ 206
Figure 3-39 RCA stiffness, dry density and moisture content versus height............................ 207
Figure 3-40 RAP elastic modulus versus time .......................................................................... 210
Figure 3-41 RCA elastic modulus versus time ......................................................................... 210
Figure 3-42 RAP PFWD and GeoGauge modulus comparison ............................................... 211
Figure 3-43 RCA PFWD and GeoGauge modulus comparison ............................................... 212
Figure 3-44 Planar and logspiral failure surfaces (Clough & Duncan, 1991) .......................... 215
Figure 3-45 Forces in a silo (Janssen, 1895)............................................................................. 216
Figure 3-46 Sensor locations .................................................................................................... 219
Figure 3-47 Vertical stress versus depth for RAP .................................................................... 221
Figure 3-48 Vertical stress versus depth for RCA .................................................................... 222
Figure 3-49 Depth versus lateral stress for RAP ...................................................................... 223
Figure 3-50 Depth versus lateral stress for RCA ...................................................................... 223
Figure 4-1 Test setup for bubbling CO2 through RCA soaked in rain water. CO2 is fed through
the bottom of each test chamber. It then bubbles up through the aggregate solution and
exits at the top of the chamber into a hose that feeds into the large plastic container filled
with water.......................................................................................................................... 232
Figure 4-2 State of Hawaii Department of Transportation’s subbase gradation along with the
gradations finer and coarser than the subbase gradation used in the leaching experiments
........................................................................................................................................... 233
Figure 4-3 pH of leachate (a) with and (b) without CO2 bubbling versus time ........................ 236
Figure 4-4 Ca2+ and Mg2+ ion concentration in the leachate with CO2 bubbled through versus
time. (a) 100% virgin basaltic aggregate – subbase gradation; (b) 50% RCA and 50%
virgin basaltic aggregate – subbase gradation; (c) 100% RCA - subbase gradation; (d)
100% RCA – coarser than subbase gradation; (e) 100% RCA – finer than subbase
gradation and (f) 90% RCA (subbase gradation) and 10% flyash .................................... 238
Figure 4-5 Ca2+ and Mg2+ ion concentration in the leachate without CO2 bubbled through versus
time. (a) 100% virgin basaltic aggregate – subbase gradation; (b) 50% RCA and 50%
virgin basaltic aggregate – subbase gradation; (c) 100% RCA - subbase gradation; (d)
100% RCA – coarser than subbase gradation; (e) 100% RCA – finer than subbase
gradation and (f) 90% RCA (subbase gradation) and 10% flyash .................................... 239
Figure 4-6 Ca2+ and Mg2+ ion concentration in the leachate of a RCA sample from Ohio
containing slag with CO2 bubbled through versus time (after Gupta and Dollimore, 2002)
........................................................................................................................................... 240
xi
Figure 4-7 X-ray diffraction results of pulverized RCA (a) before; and (b) after CO2 bubbling
through .............................................................................................................................. 244
Figure 4-8 (a) SEM image of an interior void in RCA sample and (b) EDS test results for RCA
before CO2 bubbling ......................................................................................................... 246
Figure 4-9 (a) SEM image of an interior void in RCA sample and (b) EDS test results for RCA
after CO2 bubbling ............................................................................................................ 247
Figure 4-10 100% RCA (subbase gradation) or Sample 3 after 95 days of CO2 bubbling
showing no appreciable tufa precipitate ........................................................................... 249
Figure 5.1 (a) and (b) Pavement eruptions; (c) and (d) White reaction product found in the base
course ................................................................................................................................ 255
Figure 5.2 SEM with EDS analysis of the white reaction product: (a) SEM image, (b) EDS
output showing the average elemental composition of spot1. .......................................... 261
Figure 5.3 XRD test results of the reaction product excavated from the field ......................... 264
Figure 5.4 Raman spectra for the reaction product from the field and from the laboratory ..... 266
Figure 5.5 XRD test results of the reaction product synthesized in the lab. ............................. 269
Figure 5.6 (a) Swelling test apparatus; (b) Apparatus compliance curve without sample; and (c)
Swell pressure as a function of time. ................................................................................ 272
Figure 5.7 (a) Deformed mesh of the AC pavement when subjected to a swelling pressure of
430 kPa with an AC Young’s modulus of 400 MPa and (b) Centerline deflection versus
Young’s modulus of the AC pavement. ............................................................................ 275
Figure 6-1 Effect of water content on Mr for RCA (Legend shows the molding water contents
and dry densities in kg/m3) ............................................................................................... 280
Figure 6-2 Effect of water content on Mr for 30%RG:70%VA (Legend shows the molding
water contents and dry densities in kg/m3). Gradation tested is shown in Figure 2-22. .. 284
xii
CHAPTER 1 INTRODUCTION
The desire for improved sustainability has steered engineers towards greener
design and construction practices. With about two billion tons of aggregate
being consumed each year in the United States, there is concern about rising
quantity of aggregate consumption, depletion of sources of virgin aggregate
and destruction of natural landscapes (Gonzalez and Moo-Young, 2004).
Consequently, local governments, including the State of Hawaii Department
of Transportation (HDOT), have been encouraged to incorporate the use of
recycled materials in their respective standard specifications.
However,
because recycled materials are not used universally and their properties can
be widely divergent, engineers are unfamiliar with their short and long term
behavior. Therefore, research on the behavior of these materials will help
alleviate doubts on their use in engineering applications.
Although many types of recycled materials exist, the scope of work is limited
to recycled glass (RG), recycled concrete aggregate (RCA) and reclaimed
asphalt pavement (RAP).
1.1 RG
Glass recycling escalated with the introduction of the bottle bill in Hawaii, the
eleventh state to adopt the bill. In November 2004, Hawaii consumers started
paying a nickel deposit for beverage containers and a penny to run the
collection and redemption program. In 2006, approximately 25,000 tons of
glass was recycled on the island of Oahu alone, making recovery and reuse
1
of post-consumer glass a high priority. The fate of recycled glass is usually
governed by economics.
1.1.1 Uses of RG
Excluding landfill disposal, the two options for glass reuse are in the container
and aggregate markets. For reuse in the glass container market, the recycled
bottles are typically first color-sorted and then melted, both of which can be
costly. The bottles may or may not be crushed. If left uncrushed, storage
volume and transportation costs increase. Ultimately, an economic analysis
involving labor, transportation, storage, energy costs and other relevant
factors have to be considered to determine the appropriate option. These
costs and factors vary from region to region but the focus herein will be on
glass reused as aggregate.
Many potential uses of RG aggregate in structural (e.g., base course,
subbase, fills, etc.) and drainage (e.g., drains, filters, wells, leachate collection
media, etc.) applications have been summarized by Wartman et al. (2004).
1.1.2 Challenges of Using RG
Working with RG may be hazardous (e.g., fine RG can cause skin irritation)
and appropriate safety procedures should be adopted. The need for such
safety procedures when working with RG along with its brittle nature and
crushability have stymied the use of more RG in the engineering profession.
However, under the right conditions, RG could have acceptable engineering
characteristics for use as fill or as aggregates (e.g., lightly loaded trench
backfill).
2
1.1.3 Properties
A literature review revealed that the shear strength of RG was previously
measured in at least four states in the country:
1.
Pennsylvania
–
project
sponsored
by
the
Department
of
Transportation (Wartman et al, 2004; Grubb et al., 2006;
Pennsylvania Department of Transportation, 2007a and 2007b)
2.
Washington – project sponsored by Clean Washington Center
(Dames & Moore, Inc., 1994; Shinn and Sonntag, 1994; Soil and
Environmental Engineers, Inc. and Re-Sourcing Associates, Inc.,
1998)
3.
Florida – project sponsored by the Department of Transportation
(Cosentino et al., 1995)
4.
Missouri – by the University of Missouri–Rolla (Browning, 1970).
Published friction angles of RG ranged from 34 to 62 for RG classified as
SP, SW and GP based on the Unified Soil Classification System (USCS).
When these friction angles are plotted versus dry unit weight, the results do
not show definitive trends. Amidst the scatter, there is somewhat of a trend
that friction angle increased with increasing dry unit weight and relative
density. The friction angle of RG classified as gravel is not clearly higher than
that classified as sand. One possible explanation may be particle crushing of
the larger fraction during shear (Ooi et al, 2008).
Other noteworthy observations on RG from the literature include:
3
1. The specific gravity of RG ranges between 2.45 and 2.52.
2. Optimum water contents range from 5.2 to 11.2 % and maximum dry
unit weights range from 17.0 to 18.7 kNm-3 based on ASTM D1557.
3. Minimum index dry densities range from 9.43 to 13.6 kNm -3 and
maximum values from 15.5 to 17.6 kNm-3.
4. Studies performed for the Clean Washington Center revealed that the
passing 19 mm fraction RG underwent some particle crushing during
modified Proctor compaction while particle crushing was minimal with
the passing 6.35 mm fraction (Dames and Moore, Inc., 1993).
5. Cosentino et al. (1995) encountered difficulty in obtaining a Proctor
moisture-density curve for RG that was mostly poorly graded. They
observed that ―glass particles spilled from the mold as the compaction
hammer contacted the‖ RG.
1.2 RAP
RAP is derived either through milling or full-depth removal. Milling involves
removal of only the top portion of the pavement. Typically this material does
not have to be processed and can be used instantaneously. Upon removal,
the gradation of milled RAP is typically finer than the original mix gradation
(RMRC, 2008). If full-depth removal is used, the entire pavement layer is
excavated and taken to a plant where it is crushed and blended to certain
gradations and specifications.
The characteristics of RAP mixtures vary
significantly from site to site. Nearly 73 million tons of RAP are processed
every year with approximately 80% being reused (Rathje et al., 2001).
4
1.2.1 Uses of RAP
RAP can be used to manufacture hot or cold mixed asphalt, as granular base
and subbase course, and as embankment fill.
According to the RMRC
(2008), if RAP is used as an embankment fill, the aggregate sizes that are
less than two inches can be mixed with soil or other fine aggregates and the
larger aggregate sizes can be used in a base course.
1.2.2 Challenges of Using RAP
One challenge with RAP is its potential to creep under constant load as
described by Cosentino et al. (2003) in their research to prepare RAP
specifications for base, sub-base, and fill. They also determined that when
standard Proctor tests are performed on RAP, a classical bell-shaped
compaction curve is not observed. Also, a sample of 100% RAP typically has
a low CBR (20% to 25%), while a blend of virgin aggregate with RAP has a
higher CBR (RMRC, 2008).
1.2.3 Properties
There has been many research endeavors on the engineering characteristics
of RAP. The compacted unit weight of RAP is in the range of 100 to 125 lb/ft 3
(FHWA, 2008).
The drained shear strength of RAP was investigated by
Rathje et al. (2002) using consolidated-drained triaxial compression tests and
the friction angle was determined to be 39 degrees.
1.3 RCA
About 95 million tons of RCA are processed each year (Rathje at al., 2001).
RCA is typically removed using a backhoe or payloader. RCA is processed
5
through crushers with magnets to remove rebar, and crushed to an
appropriate gradation.
The characteristics of RCA vary significantly from
each site, as the concrete mixture is different for each job.
1.3.1 Uses of RCA
A study by the New Jersey Department of Transportation (Bennert and
Maher, 2008) revealed that some states have used RCA as a base course,
subbase course, pipe bedding, surface course aggregate and subgrade soil
stabilizer. The RMRC (2008) added bulk fill material, flowable fill aggregate,
shoreline protection and gabions as other possible uses.
1.3.2 Challenges of Using RCA
According to Chesner Engineering (2001), a potential problem with the use of
RCA is tufa formation. Tufa, which is calcium carbonate, has a tendency to
clog geotextiles or drains leading to premature failure of infrastructure. They
also suggest that the RCA may cement the aggregates together thereby
making the RCA less permeable, which could be problematic if RCA is used
as a base or subbase. RCA has a high water absorbance, which may yield
unusually high optimum moisture contents. Also, the use of RCA in the field
may cause increased corrosion because of its high pH (Chesner Engineering,
2001). Other concerns when using RCA include: (a) alkali silica reaction; (b)
sulfate attack; (c) alkali carbonate reaction; and (d) reaction with aluminum.
These reactions occur when RCA is exposed to the various reagents such as
silica, sulfates, a certain type of carbonate aggregate and aluminum,
respectively.
6
1.3.3 Properties
According to the RMRC Guidelines (2008), processed RCA is typically more
angular, rougher, has a lower specific gravity and a higher absorption than
the virgin aggregate that it is derived from. RCA has high alkalinity due to the
cement paste. In the RMRC Guidelines (2008), RCA is said to have an LA
Abrasion of 20 to 45% and a CBR of 94 to 148%. Also, because RCA has a
higher absorption, the optimum moisture content is significantly larger than
the virgin aggregate that it is derived from (Chesner Engineering, 2001).
Using consolidated-drained triaxial compression tests, the drained friction
angle of RCA was determined to be 54º by Rathje et al. (2002).
RCA also has the ability to strengthen over time through hydration and
pozzolanic reaction.
This is especially true in RCA with finer gradations.
There is usually some cement that has not been hydrated in concrete
because of the production of calcium-silicate-hydrate, which forms around the
cement and prevents water from reaching the unhydrated cement
(Blankenagel, 2005).
Therefore, the finer the RCA is crushed, the more
unhydrated portions are revealed and available for additional reaction.
1.4 OBJECTIVES
As part of this project, the current HDOT specifications on the use of RG,
RCA and RAP in the unbound granular layers (base course, sub-base course
and backfill) were reviewed. Revisions are proposed to realize the benefits of
using recycled materials. Prior to revising the specifications, major issues
7
relating to use of these recycled materials were identified.
The following
research objectives are intended to address some of these issues:
1. Review the current HDOT specifications (Sections 203 Excavation
and Embankment, 204, Excavation and Backfill for Miscellaneous
Facilities, 205 Excavation and Backfill for Bridge and Retaining
Structures, 301 Plant Mix Asphalt Concrete Base Course, 304
Aggregate Base Course, 305 Aggregate Subbase Course, 306
Untreated Permeable Base Course, 624 Water System, 625 Sewer
System, 703 Aggregates, 717 Cullet and Cullet-Made Materials)
and suggest edits to incorporate the use of recycled materials.
2. Material characterization of the RG, RCA and RAP for use as a
base/subbase and fill.
Bearing
Ratio
These include shear strength, California
(CBR),
resilient
modulus
and
permanent
deformation.
3. Assess the compactability of RAP and RCA using a variety of
devices
such
as
the
nuclear
densometer,
time
domain
reflectometry, portable falling weight deflectometer and Geogauge.
4. Investigate the potential for tufa formation with local RCA.
5. Perform forensic investigation on the heave of a pavement
supported on a base course containing recycled materials.
1.5 ORGANIZATION OF REPORT
Chapter 2 presents a study to characterize the three types of recycled
materials. In Chapter 3, the compactability of RAP and RCA are discussed.
8
Chapter 4 presents the potential of the local RCA for tufa formation.
A
forensic investigation of the heave of a pavement supported on a base course
containing recycled materials is presented in Chapter 5. The major lessons
learnt from this research and its implications on the specifications are
discussed in Chapter 6. Revisions to HDOT‘s specifications are contained in
the Appendix.
9
CHAPTER 2 MATERIAL CHARACTERIZATION
This chapter discusses the index properties, resilient modulus and permanent
deformation characteristics of the recycled materials tested in this study.
2.1 MATERIAL SOURCE
Virgin aggregate (VA) and the three types of recycled materials were acquired
from Grace Pacific Corporation‘s Makakilo quarry, on the island of Oahu,
Hawaii. In Hawaii, it is customary for the quarries to distinguish between
Type A and Type B basalt. Used mostly in the manufacture of concrete and
hot mix asphalt, Type A basalt meets the requirements of American Society
for Testing and Materials (ASTM) C33 for concrete aggregate and ASTM
D448 for road and bridge construction while the inferior Type B basalt does
not.
Generally, the latter is vesiculated and is used in the layers below
pavements (base, subbase and fill).
Thus, RAP and RCA contain the
superior Type A basalt while the VA is the inferior Type B variety that
purportedly meets HDOT‘s base course requirements. .
While RAP and RCA were crushed by Grace Pacific, the RG was provided to
Grace Pacific by the City and County of Honolulu pre-crushed. RCA from
different sources were not stockpiled separately, as records on the sources of
RCA were not readily available. RAP was crushed into 2 sizes: passing 3/4
inch (19 mm) and passing 3/8 inch (9.5 mm).
10
2.2 GRAIN SIZE DISTRIBUTION
Prior to sieving, the VA, RCA and RG were oven dried at 110°C. RAP was air
dried in the sun for five days. Then a representative sample of each material
was dry-sieved (AASHTO T27) and wet-sieved (AASHTO T11). Gradation
curves using the wet sieve method generally showed slightly more fines.
However, only the dry sieve gradation curves are presented.
The gradation of each recycled material was compared with the HDOT
requirements for base, subbase and fill (Figures 2-1 through 2-6).
VA
gradation was also compared with HDOT requirements for base course
(Figure 2-7).
In summary, none of the recycled materials fit the HDOT
gradation requirements for base, subbase or fill, suggesting that they have to
be blended to meet HDOT gradation requirements prior to use. The VA did
meet HDOT‘s requirements of 1.5-inch nominal untreated base course.
11
#200 Sieve0.075mm
100%
#4 Sieve - 4.75 mm
76.2 mm
Percent Passing (%)
80%
60%
40%
2.5'' Max. Nominal
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-1 Comparison of grain size distribution of recycled materials with
HDOT‘s 2.5-inch maximum nominal untreated base course requirements
#200Sieve 0.075mm
100%
#4 Sieve - 4.75 mm
50.8 mm
Percent Passing (%)
80%
60%
40%
1.5'' Max. Nominal
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-2 Comparison of grain size distribution of recycled materials with
HDOT‘s 1.5-inch maximum nominal untreated base course requirements
12
#200Sieve 0.075mm
100%
#4 Sieve - 4.75mm 25.4 mm
Percent Passing (%)
80%
60%
40%
0.75'' Max. Nominal
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-3 Comparison of grain size distribution of recycled materials with
HDOT‘s 0.75-inch maximum nominal untreated base course requirements
#200Sieve 0.075mm
100%
#4 Sieve - 4.75mm
63.5 mm
Percent Passing (%)
80%
60%
40%
Top 6''Subbase
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-4 Comparison of grain size distribution of recycled materials with
HDOT‘s top 6-inch subbase requirements
13
#200Sieve 0.075mm
100%
#4 Sieve - 4.75mm
152.4 mm
Percent Passing (%)
80%
60%
40%
Below Top 6''Subbase
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-5 Comparison of grain size distribution of recycled materials with
HDOT‘s requirements for subbase below top 6 inches
#200Sieve 0.075mm
100%
#4 Sieve - 4.75mm
152.4 mm
Percent Passing (%)
80%
60%
40%
Embankment Fill
RCA
20%
RAP
RG
0%
0.01
0.1
1
10
Sieve Size (mm)
100
1000
Figure 2-6 Comparison of grain size distribution of recycled materials with
HDOT‘s embankment fill requirements
14
100%
#200 Sieve - 0.075 mm
50.8mm
1.5'' Maximum Nominal
80%
Percent passing (%)
#4 Sieve - 4.75mm
VA
60%
40%
20%
0%
0.01
0.1
1
Sieve size (mm)
10
100
Figure 2-7 Comparison curves of VA with HDOT‘s 1.5-inch maximum nominal
untreated base course requirements
2.3 SPECIFIC GRAVITY AND ABSORPTION
Specific gravity and absorption were measured in accordance with AASHTO
T84 and AASHTO T85 for fine and coarse aggregates, respectively. Samples
were tested using materials in their as-received gradation. The test results
are summarized in Table 2-1. From this table, the finer recycled aggregates
have consistently lower specific gravities and higher absorptions than the
coarser ones. Among the recycled aggregates, the absorption of RCA is
highest (11.8%) and that of RG the lowest (0.9%). For the VA, the apparent
specific gravity for the fine aggregate is larger than that of the coarse
15
aggregate, probably because the larger Type B basalt aggregates contain
more vesicles, making them difficult to be completely de-aired.
Table 2-1 Specific gravity and absorption
1
2
VA
Bulk specific
gravity
Bulk specific
gravity
3
(SSD)
Apparent
specific
gravity
Absorption
VA
RG
RCA
RAP
Fine
Coarse
Fine
Coarse
Fine
Coarse
Fine
Coarse
Fine
Coarse
2.26
2.33
2.25
2.37
2.46
2.50
2.13
2.45
2.17
2.54
2.49
2.48
2.49
2.52
2.48
2.51
2.38
2.59
2.31
2.61
2.95
2.77
2.95
2.80
2.51
2.52
2.84
2.85
2.52
2.72
10.5%
6.8%
10.5%
6.5%
0.9%
0.2%
11.8%
5.7%
6.3%
2.5%
Notes
1, 2 Duplicate tests were conducted for VA.
3 SSD = saturated surface dry
2.4 LA ABRASION
LA Abrasion tests were conducted in accordance with AASHTO T96 to
provide a measure of the aggregate‘s durability to impact loading.
LA
abrasion was measured for different gradings because the as-received
recycled materials and VA all have different gradations. The test results are
shown in Table 2-2. LA abrasion values for RCA and VA are comparable and
are higher than those for RAP.
This is reasonable since RCA contains
cement paste which is brittle and easily degradable while the VA consists of
the lower grade Type B basalt. The asphalt coating protects the already
durable Type A basalt in RAP from degradation.
16
Table 2-2 LA abrasion test results of four materials
Material
VA
RCA
RAP
RG
Grading1
Weight after
test
Weight
before test
Percent of
weight loss
(g)
3572
3669
3494
3626
3472
4106
4122
3334
3647
(g)
5000
5000
5000
5000
5000
5000
5000
5000
5000
(%)
29%
27%
30%
27%
31%
18%
18%
33%
27%
A
B
D
A
D
B
C
C
D
Currently, HDOT‘s maximum allowable LA abrasion for untreated base
course is 40%, which is larger than any of the values obtained. HDOT does
not have a minimum LA abrasion requirement for subbase and fill. So from
an LA abrasion viewpoint for base course, all materials meet the HDOT
requirement.
2.5 COARSE AGGREGATE VOID CONTENT
Coarse aggregate void content test was conducted in accordance with
AASHTO TP56-99 Method A.
shape and texture.
The void content depends on the particle
Using the uncompacted void content, aggregate
angularity of different materials with the same grading can be compared. A
decrease in the void content is associated with more rounded, spherical,
smooth surfaced coarse aggregate or a combination of these factors. The
coarse aggregate void content of each material is shown in Table 2-3. The VA
17
has the highest coarse aggregate void content (56.7%). RCA, RAP and RG
have similar values.
Table 2-3 Void content of coarse aggregate of each material
Bulk Specific Gravity Used
Material
Void Content
2.77
VA
56.7%
50.0%
2.54
RAP
2.45
RCA
48.2%
2.50
RG
46.3%
2.6 SAND EQUIVALENT TEST
Sand equivalent (SE) tests were conducted in accordance with AASHTO
T176. The test results are summarized in Table 2-4. SE is used to determine
the characteristics of the finer grained portion of cohesionless soils. It is
determined by performing a sedimentation test. The fraction of sand that
passes through a 5 mm sieve is placed into a cylinder of water containing a
flocculent, shaken and allowed to stand for twenty minutes. A deposit of sand
of height, h, forms in the flocculated material of height, H, above which lies
clear water. The sand equivalent, SE = h/H. If SE > 30%, the material is not
plastic. The higher the SE, the higher is the percentage of sand and silt size
particles. Typically, clays have sand equivalent between 0 and 5%, silty clays
between 6 and 10%, clayey silts between 11 and 30%, clayey fine sands
between 30 and 40%, and silty fine sands above 40%.
18
Table 2-4 Sand equivalent (SE) test results
Material
VA
RCA
RAP
RG
Sand Equivalent
49%
68%
73%
92%
HDOT‘s minimum allowable SE value for untreated base and subbase are
30% and 25%, respectively. The largest SE value obtained was 92% for RG,
and the smallest was 49% for VA. Therefore, from a SE perspective, all
materials meet HDOT requirements for base and subbase. HDOT has no
minimum SE requirement for fill.
2.7 ATTERBERG LIMITS
Atterberg limit tests conducted include the plastic and liquid limit tests. The
shrinkage limit test was not performed. Plastic limit test was conducted in
accordance with AASHTO T90, and the liquid limit test was conducted in
accordance with AASHTO T89. Test results showed that the finer fractions of
all four materials are classified as non-plastic (NP).
2.8 ASPHALT CONTENT OF RAP
The RAP asphalt content was measured in accordance with AASHTO T 308
using a NCAT asphalt content tester (ignition oven). Asphalt binder in the
RAP is burnt in the oven and the asphalt content is calculated as the
difference between the initial RAP aggregate mass and the residual mass
after burning. The moisture-free asphalt content is 5.8%.
19
2.9 CALIFORNIA BEARING RATIO
The California Bearing Ratio (CBR) test is used to evaluate the strength
characteristics of the material for pavement support. This section presents
the CBR test results for VA, RCA, RAP and RG. All CBR samples were first
prepared to meet the State of Hawaii Department of Transportation‘s (HDOT)
embankment fill gradation.
This gradation was chosen because it was
anticipated that it would yield the lowest CBR as compared to the base or
subbase. CBR tests were also performed on blends of VA with each of the
three recycled materials to evaluate the effect of blending ratio on CBR.
Then, the effects of gradation on CBR were also evaluated for RCA and RAP
using two types of HDOT gradations: embankment fill (finer) and base course
(coarser).
2.9.1 OVERVIEW OF THE CBR TEST
The equipment and procedure for the CBR test are detailed in AASHTO T
193 and ASTM D1883. There are three stages in a CBR test. First, the
specimen is dynamically compacted in a 6-inch (152 mm) diameter mold.
Second, the specimen is soaked for 4 days with a surcharge load applied.
Soaking the sample simulates the worst case moisture scenario in the field
and the surcharge simulates the overburden due to the pavement. Third, with
the same surcharge in place, a standardized piston having an area of 5806
mm2 (3 inch2) is used to penetrate the soil in the mold at a rate of 1.27 mm
(0.05 inch) per minute (Figure 2-8). Generally, the load at 2.54 mm (0.1-inch)
penetration is used to compute the CBR. The CBR is defined as the ratio of
20
the stress at 2.54 mm (0.1-inch) penetration to that of a standard. Standard
values corresponding to a high quality crushed stone are summarized in
Table 2-5. If the CBR at 5.08 mm (0.2-inch) penetration is higher than that at
2.54 mm (0.1-inch) penetration, the value at 5.08 mm (0.2 inch) penetration is
used.
Table 2-5 Standard load for high quality crushed stone material
Penetration
(inch)1
Standard load for crushed stone
(psi)2
0.1
1000
0.2
1500
0.3
1900
0.4
2300
0.5
2600
Notes
1 1 inch = 25.4 mm
2 1 psi = 6.895 kPa
2.9.1.1 Compaction
The moisture-density relationships were established in accordance with
AASHTO T180 Procedure D or ASTM D1557 Procedure C. The material was
compacted in a 152.4-mm-diameter mold in 5 lifts with each lift receiving 56
blows. The compaction was facilitated using a Boart Longyear mechanical
compactor that is bolted to the concrete floor. The compactor has a pieshaped rammer. Before use, the mechanical compactor was calibrated in
accordance with ASTM D 2168. The weight of the rammer was adjusted until
21
the deformation of lead cylinders from the mechanical compactor and a 10-lb
manual modified Proctor hammer are equal.
Figure 2-8 Penetration portion of CBR test (Porter 1949)
2.9.1.2 Soaking
After compaction, the samples were soaked for 4 days in a tub of water. A
surcharge of 6.8 kilograms was applied to the sample during soaking and
CBR testing to simulate the pavement overburden.
The soaking was
necessary to simulate the worst case scenario in the field. Very little swell
was detected in all the materials during the soaking period.
22
2.9.1.3 CBR Testing
The CBR testing equipment consists of a loading frame supporting a plunger
which penetrates the sample in the mold (Figure 2-9).
Figure 2-9 CBR test set up
23
A data acquisition system consisting of the following was used to record the
load and penetration during the test:
10,000-lb rated load cell (Sensortronics 6000 1A-10K)
Two Linear Variable Differential Transducers (LVDT) with a range of
25.4 mm (Schaevitz 1000MHR)
Signal conditioner (PMG Precision Instruments SC-5B AC Transducer)
Computer with analog to digital (A/D) board (Metrabyte)
ATS software (Version 3.1)
During the test, the voltage output from the load cell and LVDTs were sent to
the signal conditioner, which converts the voltage to an analog output. This in
turn was translated by the A/D board to load and displacement. The LVDTs
were placed diametrically opposite, with the average displacements used for
determination of CBR.
After the test, a stress-displacement plot was made to interpret the CBR
value. In some cases, the initial stress-penetration curve is not linear, but
concave upward. For such cases, the CBR values were corrected using the
method as specified in AASHTO T 193.
24
2.9.2 CBR TEST SAMPLE GRADATION AND RESULTS
2.9.2.1 Sample Gradation
The target gradation for CBR samples of VA, RCA and RAP is identical to the
finer end of the range for embankment fill per HDOT specification (Figure 210). The only exception is that the maximum aggregate size was limited to ¾
inch (19 mm) as required by AASHTO T193. For RG [maximum nominal
aggregate size = ⅜ inch (9.5 mm)] and its blends with VA, a finer gradation
(Figure 2-11) was adopted due to the unavailability of the larger aggregates.
100%
Percent Passing (%)
80%
60%
2.5'' Max. - Base
1.5'' Max. -Base
3/4'' Max. -Base
40%
Top 6'' Subbase
Below top 6'' Subbase
20%
Fill
CBR Test Gradation
0%
0.01
0.1
1
10
Aggregate Size (mm)
100
1000
Figure 2-10 CBR test gradation for VA, RCA, RAP and their blends with
respect to HDOT gradations (upper bound) for fill, subbase and base course
25
9.5mm, 100% 19mm, 100%
100%
Percent Passing (%)
80%
60%
40%
20%
RG&VA blends
VA, RCA and RAP
0%
0.01
0.1
1
10
100
Aggregate Size (mm)
Figure 2-11 CBR test gradation for RG & VA blends
2.9.2.2 CBR
At least six CBR tests were conducted for each material. The results are
presented as water content versus dry unit weight in Figure 2-12a and water
content versus CBR in Figure 2-12b.
26
22
VA
RCA
Dry Unit Weight (kN/m3)
21
RAP
RG
20
19
18
17
16
3
6
9
12
15
18
21
Water Content (% )
(a)
300
250
VA
RCA
CBR (%)
200
RAP
RG
150
100
50
0
3
6
9
12
15
18
21
Water Content (% )
(b)
Figure 2-12 CBR test results (a) Dry unit weight versus water content and (b)
CBR versus water content
27
Figure 2-12a shows that RAP has the lowest optimum water content and the
highest maximum dry density, while RCA has just the opposite. The largest
densities were observed in RAP probably because of the ability of the
asphalt-coated particles to slip into a denser configuration. VA and RG have
comparable dry unit weights but different optimum water contents.
The
optimum water contents of RAP and RG are similar.
Figure 2-12b shows that the maximum CBR occurred at the optimum water
content and maximum dry unit weight for all four materials. At optimum, RCA
is strongest (CBR = 300%) possibly due to hydration of the previously
unhydrated cement particles and RAP weakest (CBR = 50%).
RAP is
weakest probably because the asphalt coating allows the particles to slip
within themselves more readily during penetration leading to higher
deformations. VA is weaker than RCA but stronger than RG.
The effect of water content on CBR is small for RAP and RG, but is significant
for VA and RCA.
2.9.2.3 Changes in Gradation after Compaction and CBR testing
To evaluate whether the gradation changed due to compaction and CBR
testing, sieve analyses were conducted after CBR testing for comparison.
Both dry and wet sieve methods were used. The results (Figure 2-13) show
that:
1) There was very little change in the gradation for RG despite the fact
that glass is known to be brittle;
28
2) The VA appears finer after testing suggesting that some particle
crushing occurred with the more vesiculated and weaker Type B basalt
aggregate;
3) There was scatter on both sides of the target test gradation for RCA
and RAP. It is not surprising for the gradations to be finer after testing.
Reasons why some of the gradations become coarser after testing can be
explained as follows. With RCA, some of the particles may have re-cemented
together after soaking and testing. As for RAP, this may be due to the fact
that the asphalt caused the particles to stick together after compaction and
CBR testing.
29
100%
CBR Test Gradation
# 1 dry sieve
Percent Passing (%)
80%
# 1 wet sieve
# 2 dry sieve
# 2 wet sieve
60%
# 3 dry sieve
#3 wet sieve
#4 dry sieve
40%
#4 wet sieve
20%
0%
0.01
0.1
1
10
Aggregate Size (mm)
100
Figure 2-13a Variation of gradation before and after compaction and CBR test
- VA
100%
CBR Test Gradation
#1dry sieve
Percent Passing (%)
80%
#2 dry sieve
#3 dry sieve
#4 dry sieve
60%
#4 wet sieve
40%
20%
0%
0.01
0.1
1
Aggregate Size (mm)
10
100
Figure 2-13b Variation of gradation before and after compaction and CBR test
- RCA
30
100%
CBR Test Gradation
# 3 dry sieve
Percent Passing (%)
80%
#3 wet sieve
#4 dry sieve
60%
#4 wet sieve
# 5 wet sieve
# 6 wet sieve
40%
20%
0%
0.01
0.1
1
10
100
Aggregate Size (mm)
Figure 2-13c Variation of gradation before and after compaction and CBR test
- RAP
100%
CBR Test Gradation
# 1 dry sieve
Percent Passing (%)
80%
# 2 dry sieve
# 3 dry sieve
60%
# 4 dry sieve
# 4 wet sieve
40%
20%
0%
0.01
0.1
1
Aggregate Size (mm)
10
100
Figure 2-13d Variation of gradation before and after compaction and CBR test
- RG
31
2.9.3 CBR OF BLENDS
As shown in Figs 2-1 through 2-6, the as-received RCA, RAP and RG did not
meet any of HDOT‘s gradation requirements for base, subbase course or fill.
Consequently, they would need to be blended prior to use. RCA, RAP and
RG were blended with VA to investigate the effects of varying blend ratios on
CBR. Two blend ratios were adopted for each material, i.e., 50% recycled
material:50% VA and 25% recycled material:75% VA. The test results are
summarized in Figures 2-14 through 2-16.
32
20
100% RCA:0%VA
3
Dry Unit Weight (kN/m )
50% RCA:50%VA
25% RCA:75% VA
19
0%RCA:100% VA
18
17
16
5
10
15
20
25
Water Content (% )
Figure 2-14a Dry unit weight versus water content for RCA blends
300
100% RCA:0%VA
50% RCA:50% VA
250
25% RCA:75% VA
0%RCA:100% VA
CBR (%)
200
150
100
50
0
5
10
15
Water Content (% )
20
Figure 2-14b CBR versus water content for RCA blends
33
25
22
100% RAP:0%VA
3
Dry Unit Weight (kN/m )
50% RAP:50% VA
25% RAP:75% VA
21
0%RAP:100% VA
20
19
18
0
5
10
15
20
Water Content (% )
Figure 2-15a Dry unit weight versus water content for RAP blends
150
100% RAP:0%VA
120
50% RAP:50% VA
CBR (%)
25% RAP:75% VA
0%RAP:100% VA
90
60
30
0
0
5
10
Water Content (% )
15
Figure 2-15b CBR versus water content for RAP blends
34
20
20
100% RG:0%VA
Dry Unit Weight (kN/m3)
50% RG:50% VA
25% RG:75% VA
19
18
0
5
10
15
20
Water Content (% )
Figure 2-16a Dry unit weight versus water content for RG blends
150
100% RG:0%VA
50% RG:50% VA
120
CBR (%)
25% RG:75% VA
90
60
30
0
0
5
10
15
Water Content (% )
Figure 2-16b CBR versus water content for RG blends
35
20
The following observations are offered:
1) With increasing %RCA, the compaction curves of the RCA/VA blends
shifted from top left to bottom right. This indicates an increase in the optimum
water content and a decrease in the maximum dry unit weight with increasing
%RCA.
2) With increasing %RAP, however, the compaction curves of the
RAP/VA blends shifted from bottom right to top left.
This indicates a
decrease in the optimum water content and an increase in the maximum dry
density with increasing %RAP.
3) For RG/VA blends, the trend in the variation of maximum dry unit
weight and optimum water content with percent RG was not definitive with
changes in %RG.
4) With increasing %RCA, the CBR curves of the RCA/VA blends shifted
from bottom left to top right. This implies that the higher the RCA content, the
higher the CBR probably due to (a) increasing Type A basalt with increasing
%RCA and (b) more re-cementation upon soaking.
5) With increasing %RAP, however, the CBR curves of the RAP/VA
blends shifted from top right to bottom left, which is opposite to RCA/VA. This
implies that the higher the RAP content, the weaker is the material probably
due to the fact that the asphalt caused the particles to deform within
themselves more readily.
36
6) For RG/VA blends, there was also no clear trend in the variation of
CBR with %RG.
2.9.4 EFFECTS OF GRADATION ON CBR OF RCA AND RAP
The effects of varying gradation on the CBR of RCA and RAP were studied.
RG was not studied because there was insufficient coarse RG aggregate (9.5
mm minus) to constitute a base course gradation. A comparison of the CBRs
was made using HDOT‘s embankment fill and base course gradations (Figure
2-17).
19, 100%
100%
3/4'' Max. Nominal
Percent Passing
80%
Base Gradation
Fill Gradation
60%
40%
20%
0%
0.01
0.1
1
Aggregate Size (mm)
10
100
Figure 2-17 Gradations for CBR Test
The coefficients of uniformity of the base course and fill are 35 and 33,
respectively, while the coefficients of curvature are 1.9 and 0.49, respectively.
The percent fines for the base course and fill are 6% and 15%, respectively.
37
Thus, the Unified Soil Classification System (USCS) symbols are GW – GM
(well graded gravel with silt and sand) for the base course and SM (silty sand
with gravel) for the fill. Based on the AASHTO classification system, the base
course and fill both fall into the A-1-a category.
The compaction and CBR curves for RCA and RAP are shown in Figures 218 and 2-19, respectively. For RCA, the base course compaction curve lies
above and to the left of that for the fill, while that for RAP lies below and to the
left.
For both RCA and RAP, the embankment fill gradation have higher
CBRs than the base course gradation.
These results are somewhat
surprising but may be explained as follows:
1) For RCA, the base course gradation is denser than the fill gradation.
This seems logical. However, it can only be theorized that (a) the finer, fillgradation CBRs are higher due to increased fines, and hence, increased
cementation after 4 days of soaking; and (b) the base course CBRs are lower
because of crushing of the brittle cement paste, especially if the paste is thick.
2) The compaction curve for RAP having a base course gradation lying
below that of the fill is somewhat surprising but may be explained as follows:
the asphalt-coated particles slip into a denser configuration quite readily with
smaller particles being able to do this more so than coarser ones. Since the
base course contains more coarse particles, this slippage cannot occur so
readily leading to lower dry unit weights and lower CBRs in the base course
gradation relative to the fill gradation.
38
20
3
Dry Unit Weight (kN/m )
Base Course
Fill
19
18
17
16
5
10
15
Water Content (% )
20
25
Figure 2-18a Effect of gradation on RCA compaction curve
400
Base Course
300
CBR (%)
Fill
200
100
0
5
10
15
Water Content (% )
20
Figure 2-18b Effect of gradation on RCA CBR strength
39
25
22
3
Dry Unit Weight (kN/m )
Base Course
Fill
21
20
19
18
0
2
4
6
Water Content (% )
8
10
Figure 2-19a Effect of gradation on RAP compaction curve
60
Base Course
Fill
CBR (%)
40
20
0
0
2
4
6
8
Water Content (% )
Figure 2-19b Effect of gradation on RAP CBR strength
40
10
2.9.5 CBR SUMMARY AND CONCLUSIONS
CBR tests were performed on three recycled materials, a basaltic VA, and
their blends having gradations that meet HDOT‘s embankment fill gradations.
The effects of varying gradations on CBRs were also studied for RCA and
RAP, wherein the CBRs of the fill and base course gradations were
compared. The following conclusions are offered:
With all materials having the embankment fill gradation, RAP had the
lowest optimum water content and the highest maximum dry unit
weight, while RCA had just the opposite. VA and RG have comparable
dry unit weights but different optimum water contents. The optimum
water contents of RAP and RG, materials with very low absorptions,
are similar but lower than those for VA and RCA.
With all materials having the embankment fill gradation, the maximum
CBR occurred at the optimum water content and maximum dry unit
weight. At optimum, RCA had the highest CBR and RAP the lowest.
VA is weaker than RCA but stronger than RG.
With all materials having the embankment fill gradation, varying the
water content had a small effect on the CBR for RAP and RG, but the
effect was significant for VA and RCA.
With all materials having the embankment fill gradation, there was very
little change in the gradation for RG after CBR testing; the VA was finer
after testing suggesting that some particle crushing occurred; there
41
was scatter on both sides of the target test gradation for RCA and
RAP. It is not surprising for the gradations to be finer after testing.
Reasons why some of the gradations became coarser after testing can
be explained as follows. With RCA, some of the particles may have recemented together after soaking and testing. As for RAP, this may be
due to the fact that the asphalt caused the particles to stick together
during compaction and CBR testing.
With increasing %RCA, the RCA/VA blends showed an increase in the
optimum water content and a decrease in the maximum dry unit
weight.
RAP/VA blends showed the opposite trend.
For RG/VA
blends, the trend was not clear.
The higher the RCA content, the stronger the material (higher CBR)
probably due to more Type A basalt present and more re-cementation
upon soaking; the higher the RAP content, the weaker the material
probably due to the fact that the asphalt caused the particles to deform
within themselves more readily; for RG/VA blends, there was no clear
trend in the variation of CBR with %RG.
The CBR of RCA is lower for the base course gradation than for the
embankment fill gradation.
This is not intuitive.
It can only be
theorized that (a) the finer, fill-gradation CBRs are higher due to an
increase in fines, and hence, increased re-cementation after 4 days of
42
soaking; (b) the base course CBRs are lower because of crushing of
the brittle cement paste, especially if the paste is thick..
The CBR of RAP is lower for the base course gradation than for the
embankment fill gradation.
This can be explained as follows: the
embankment fill gradation samples have very high densities due to the
ability of the asphalt-coated particles to slip into a denser configuration.
This deformation is more pronounced in the fill gradation because
smaller particles are more able to slip into a denser configuration than
coarser ones. Since the base course contains more coarse particles,
this slippage cannot occur so readily leading to lower dry unit weights
and lower CBRs in the base course gradation relative to the fill
gradation.
43
2.10 RESILIENT MODULUS
This section presents the results of resilient modulus (Mr) testing on VA, RAP,
RCA, 50% RAP:50% VA and 50% RCA:50% VA, all having gradations that
mostly conform to the State of Hawaii Department of Transportation‘s (HDOT)
base course gradation. In addition, one blend of VA with RG was tested
(30% RG:70% VA). Because the RG was crushed very fine (9.5 mm minus),
this ratio had to be utilized so that the blend could still meet HDOT‘s base
course gradation requirements.
2.10.1 LITERATURE REVIEW
2.10.1.1 Use of Mr in Pavement Design
The concept of Mr was originally introduced by Seed et al. (1962).
Mr
provides a measure of the stiffness of the soil under confinement and
repeated loading.
It is defined as the deviator stress (d) divided by the
recoverable axial strain (r) and is usually obtained from repeated load cyclic
triaxial tests. It is a necessary and important input parameter required in the
Mechanistic-Empirical Pavement Design Guide or MEPDG (ARA Inc. 2004).
The MEPDG‘s philosophy is that the level of engineering effort to obtain M r
should be consistent with the relative importance, size and cost of the design
project. In light of this, the material stiffness characterization may fall into one
of the following three input levels. Level 1 represents the highest reliability
where the Mr is measured directly through testing.
In Level 2, the Mr is
estimated from correlations with common soil parameters. In Level 3, the Mr
44
is estimated based on just the material classification.
Clearly, increasing
levels have successively lower reliabilities.
In National Cooperative Highway Research Program (NCHRP) Synthesis
382, Puppala (2008) summarized two nationwide surveys with input from
DOT engineers in the materials/geotechnical division and in pavement
design.
The surveys revealed the state of practice for determining M r of
bases and subgrades. It was reported that overall satisfaction in the use of
Mr for pavement design is low mainly attributable to the following: 1) constant
modification of test procedures (in chronological order AASHTO T274-82,
AASHTO T292-91, AASHTO T294-92, Long Term Pavement Performance
(LTPP) Protocol P46-96, NCHRP 1-28 1997, AASHTO T307-99, AASHTO
T307-03, and NCHRP 1-28A, 2003), 2) complicated laboratory or field test
procedures and correlations required to determine Mr, and 3) design-related
issues. Other pertinent survey findings are cited below.
Of the 41 respondents from the 50 state DOTs, 22 use M r testing in routine
pavement design.
12 of the 41 respondents use laboratory methods to
determine Mr, with 9 using Repeated Load Triaxial (RLT) tests. With respect
to RLT tests, four follow the AASHTO T-307 procedure, two the NCHRP 128A harmonized procedure, and the remainder the AASHTO T-294, LTTP
TP-46 or a modified Mr test method.
Problems relating to laboratory Mr
testing, according to the respondents, are summarized in Figure 2-20.
45
Figure 2-20 Problems related to laboratory Mr test (Puppala 2008)
Direct correlations between Mr and other soil properties (e.g., CBR or Rvalue) were used by 6 respondents for unbound bases (Figure 2-21). None
utilize correlations between Mr and stress levels in the unbound bases where
the model (ki) parameters are regressed with common soil properties.
As for the reliability of correlations between Mr and common material
properties, 8 agencies characterized the level of reliability of the correlations
for unbound bases as fair, and only 3 noted as very good to good. ―Most
DOTs did not reply to this question, implying that they do not use correlations
for moduli predictions‖ (Puppala 2008).
Puppala (2008) observed that reported Mr values of unbound granular base
and subbase ranged from 10 to 45 ksi (about 70 to 310 MPa).
46
Figure 2-21 Types of correlations used for predicting Mr by the various state
DOTs (Puppala 2008)
In the State of Hawaii, pavement design is mainly based on R-value.
Although Mr is not currently used in pavement design, it may be in the
foreseeable future.
2.10.1.2 Factors Influencing Mr of Unbound Granular Material
Li and Selig (1994) identified three factors that influence M r: stress state, soil
type/characteristics, and soil physical state.
Hicks (1970) and Hicks and
Monismith (1971) showed that Mr increases with increasing confining stress
or bulk stress. For granular materials, it is common for Mr to increase with
increasing deviator stress, implying a strain hardening response, whereas
cohesive soils typically exhibit a strain softening behavior.
47
Uthus (2007)
concluded that in granular materials, the effect of confining stress overwhelms
that of the deviator stress.
Mr of geomaterials decreases as the moisture content increases. Moisture
has two separate effects (Christopher et al., 2006). First, it affects the matric
suction which in turn affects the effective stress and stiffness. Second, it can
affect the cementation between soil particles.
Mr also decreases with
decreasing dry density or relative compaction.
2.10.1.3 Mr Test Procedures
Many Mr test protocols exist.
In Europe, the European Committee for
Standardization (CEN) EN 13286-7 (2004) is prevalent. In the USA, the most
recent Mr test procedures are AASHTO T307 and NCHRP 1-28A (CTC &
Associates LLC, 2008). Some of the major differences between T 307 and
NCHRP 1-28A are highlighted below:
1) AASHTO T 307 divides the materials into two categories depending on
function. Subgrade soils share the same test load sequence irrespective of
whether the material is cohesive or cohesionless. Base/subbase materials
have a separate test load sequence. NCHRP 1-28A specifies three separate
materials by gradation. Different test load sequences exist for each of the
three material categories.
2) Test load sequences - In AASHTO T 307, the large deviator stresses
are applied to the sample early on in the test. In NCHRP 1-28A, the sample
48
experiences the largest deviator stress towards the end of the test and so it
has the advantage of not prematurely failing weaker samples.
3) Placement of load cells and LVDTs - AASHTO T 307 specifies external
load cell and LVDTs, while NCHRP 1-28A specifies internal load cell and
LVDTs.
4) Conditioning - AASHTO T307 requires between 500 and 1000
repetitions of the conditioning deviator stress. If the sample height is still
decreasing after 500 cycles, the number of cycles should be increased to
1000. In NCHRP 1-28A, 1000 load repetitions are required.
2.10.1.4 Mr Models
Models for estimating Mr are usually expressed as a function of the stress
state. The most general form of a Mr model is the three-parameter model,
which can be written as follows (Ooi et al., 2004):
Mr = k1pa[f(c)]k2[g(s)]k3
(2.1)
where f(c) is a function for confinement, g(s) is a function for shear and k1, k2
and k3 are model constants. In this equation, the function for confinement
can be expressed in terms of the minor principal stress (3), bulk stress ( =
1 + 2 + 3), or octahedral normal stress (also known as mean confining
stress, oct = p = /3), where 1, 2 and 3 are the major, intermediate and
minor principal stresses, respectively.
The function for shear can be
expressed in terms of the deviator stress, d or q, or octahedral shear stress
49
(oct = √2q/3). This three-parameter model is versatile in that it applies to all
soils and aggregates. Several variations of the Mr models exist, some of
which are summarized in Table 2-6.
The K- model proposed by Seed et al. (1967) has been widely used in the
past for modeling Mr of granular materials. Two limitations of this model
include: (1) it is not dimensionally correct. The Mr and bulk stress can be
normalized by the atmospheric pressure prior to raising the latter to a power;
(2) multiple stress conditions can give the same modulus.
For example,
combinations of low confining stress and high deviator stress can result in the
same bulk stress and hence, the same Mr, as high confining stress and low
deviator stress.
A total of 6 Mr models may arise based on the three types of confinement and
two types of shear stress combinations in Equation 2.1. When using these 6
models for a soil in an isotropic stress state, Mr = 0 when k3 > 0 and Mr → ∞
when k3 < 0. By adding 1 to the normalized octahedral shear stress in the
function for shear yields the MEPDG model.
50
Table 2-6 Summary of available Mr models
Author
Equation
Biarez (1961)
E = K (σm)n
Dunlap (1963)
M r k1 p a 3
pa
Seed et al. (1967) M r k1 k2
Seed et al. (1967)
Shackel (1973)
k2
K- model
M r k1 p a
pa
k 2 k3
M r k1 oct oct
Primarily for granular soils.
k2
k2
Uzan (1985)
M r k1 p a d
pa pa
Normalized Shackel (1973)
model
k3
k2
k3
Witczak and Uzan
oct
M r k1 p a
(1988)
pa pa
k2
k3
Pezo (1993)
3 d
M r k1 p a
pa pa
0.5
Kolisoja (1997)
M r A(nmax n) p a
pa
k2
Ni et al. (2002)
M r k1 p a 1 3 1 d
pa
pa
Ooi et al. (2004)
d
1
M r k1 p a 1
p a
pa
Ooi et al. (2004)
oct
1
M r k1 p a 1
p a
pa
ARA, Inc. (2004)
M r k1 p a 1 oct
pa
pa
Gupta et al. (2007)
3k 6
M r k1 p a b
pa
k2
k2
k2
Remarks
E = Secant modulus
K, n are empirical constants
k2
k 7 oct
pa
k3
Adopted in the 1993 AASHTO
design guide
Effect of density included
n = porosity of the aggregate
k3
k3
k3
Adopted in the MEPDG (ARA
Inc., 2004) and the NCHRP 128A procedure
μ − μw :matric suction
1 (u a u w ) a
1, 1: regression constants
k3
1
Notes: k1, k2, k3, k6 and k7 are model constants
pa = atmospheric pressure =14.7 psi = 101.3 kPa
1, 2 and 3 are the major, intermediate and minor principal stresses, respectively
= bulk stress = 1 + 2 + 3
m = mean normal stress = /3 = oct = p
d = deviatoric stress = 1 – 3 = q
oct = octahedral shear stress = ⅓[(1 − 2)2 + (2 − 3)2+ (3 − 1)2]½ =√2d /3.
51
Another generation of models can arise with 1 added to both the normalized
confining and shear terms. This is reasonable because without adding unity
to the normalized confining stress, a soil with no confinement will have a zero
Mr. This is obviously not true. In addition, Ooi et al. (2004) showed that these
models provide a superior fit to test data.
The Mr models can be extended by correlating the model constants ki with
basic soil parameters to take into account the effects of moisture, density,
gradation and other factors on Mr. These correlations typically work well for
the local soils that the models were developed for. Problems can arise when
the correlations are applied to the same type of soils elsewhere (Wolfe and
Butalia, 2004 and Malla and Joshi, 2006). This method of correlating the
model constants ki with basic soil parameters is mostly available for finegrained soils and is rarely applied to coarse aggregates. This is probably
because the Mr of bases and subbases are less sensitive to variations in
water content and dry density than fine-grained soils.
2.10.1.5 Recent Studies on Mr of RCA and RAP
Based on a literature review, Mr of RCA and RAP have been studied by
several researchers, some of which are summarized in Table 2-7. No study
on Mr or permanent deformation of RG was found.
52
Table 2-7 Mr studies on RCA and RAP
Reference
Bennert et al.
(2000)
Country
Recycled
Highlights from Study
Material
USA
RCA and
RAP
RAP and RCA all showed higher Mr
than the dense-graded aggregate base
course (DGABC) in New Jersey.
RCA
The original concrete compressive
strength, the amount of soft material in
the RCA, and the flakiness index of the
RCA can significantly affect the Mr.
Nataatmadja
and Tan
(2001)
Australia
Molenaar and
van Niekerk
(2002)
Netherlands RCA
Degree of compaction is the most
important factor affecting Mr.
Blankenagel
and Guthrie
(2006)
USA
RCA
Both demolition and haul-back recycled
concrete material had marked stiffening
after a 7-day curing period.
RCA
Mr of RCA is higher compared to gravel
or crushed rock;
Mr = 350 - 650 MPa with highest values
for open-graded material.
RAP
Mr decreased when RAP content
increased from 0 to 25 %. Mr then
steadily increased as the RAP content
increased from 25% to 100%.
Aurstad et al.
(2006)
Guthrie et al.
(2007)
Norway
USA
Kim and Labuz
(2007)
USA
RAP
Saeed (2008)
USA
RCA and
RAP
53
Mr increased with an increase in
confining pressure. There was little
change in Mr with increasing deviator
stress. Specimens with water contents
at ~ 65% the value at optimum were
stiffer than those at optimum regardless
of confining pressure. Base materials
with various RAP percentages
performed similar to 100% virgin
aggregate in terms of stiffness and
strength.
The blends of RCA and VA, RAP and
VA had lower stiffness due to the good
performance of the VA selected; RAP
and VA blends showed less water
content susceptibility while the RCA and
VA blends showed the opposite.
2.10.2 CHARACTERISTICS OF MATERIALS, TEST EQUIPMENT AND
PROCEDURES
In this section, the gradation and compaction curves of the materials
subjected to Mr testing are first described.
This is followed by the test
equipment and procedure.
2.10.2.1 Gradation and Compaction Curves
The gradations for the Mr test samples are shown in Figure 2-22.
This
gradation differs from the base course gradation used in the CBR tests
(Figure 2-17) because of a lack of fines at this stage of the research. For the
RG blend, because RG was crushed to 3/8‘‘ minus, there was insufficient
coarse RG aggregate to achieve the target gradation.
Hence a finer
gradation as shown in Figure 2-22 was used for the RG blend. According to
Croney and Croney (1997), ―the grading …… of crushed rock and crushed
gravel have only a small influence on the modulus.‖
The moisture-density relationship for each material (Figures 2-23a to 2-23f)
was determined using a 152-mm-diameter Proctor mold in accordance with
AASHTO T180 Method D, wherein each sample was compacted using 5 lifts,
and each lift received 56 blows from a 4.5-kg-hammer dropping 46 cm. It was
difficult to obtain the dry unit weight (d) and water content (w) wet of optimum
for 4 of the 6 materials because these samples could not retain the moisture
(water leaked from the bottom of the mold during compaction). For these
materials, the values at optimum are interpreted as shown in Table 2-8.
Water contents were measured by placing the entire mold and samples in the
54
oven at 110ºC for several days until the water content stabilized. For RAP,
the oven temperature was set at 60ºC.
The specific gravities (Gs) in Figure 2-23 were calculated based on the
specific gravities of the fine and coarse aggregate, and their percent
composition in the blend as follows: Gs = (% fine + % coarse)/(% fine/Gs fine +
% coarse/Gs coarse) where Gs fine and Gs coarse are the apparent specific gravities
of the fine and the coarse aggregate from Table 2-1. For the blends, the
same methodology was used.
100%
Mr Test Gradation except for RG&VA Blends
Percent Passing (%)
80%
Mr Test Gradation for RG&VA Blends
HDOT's 3/4'' Max. Nominal Base Course
60%
40%
20%
0%
0.01
0.1
1
Aggregate Size (mm)
10
Figure 2-22 Sample gradation used for Mr test
55
100
23
Dry Unit Weight (kN/m3)
VA
22
Zero Air Void Curve
21
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (%)
Figure 2-23a Compaction curve for VA (Gs = 2.85 for ZAV curve)
23
Dry Unit Weight (kN/m3)
RCA
22
Zero Air Void Curve
21
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (%)
Figure 2-23b Compaction curve for RCA (Gs = 2.85 for ZAV curve)
56
RCA&VA
22
3
Dry Unit Weight (kN/m )
23
Zero Air Void Curve
21
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (%)
Figure 2-23c Compaction curve for RCA&VA (Gs = 2.85 for ZAV curve)
23
RAP
Dry Unit Weight (kN/m3)
22
Zero Air Void Curve
21
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (%)
Figure 2-23d Compaction curve for RAP (Gs = 2.64 for ZAV curve)
57
22
RAP&VA
21
Zero Air Void Curve
3
Dry Unit Weight (kN/m )
23
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (%)
Figure 2-23e Compaction curve for RAP&VA (Gs = 2.74 for ZAV curve)
22
RG&VA
3
Dry Unit Weight (kN/m )
23
Zero Air Void Curve
21
20
19
18
17
0%
4%
8%
12%
16%
20%
Water Content (% )
Figure 2-23f Compaction curve for RG&VA (Gs = 2.74 for ZAV curve)
58
Table 2-8 Water contents and dry densities of Mr test samples
Material
VA
RAP
RAP&VA
RCA
RCA&VA
RG&VA
Target Water
Content (%)
8.8
8.8
8.8
8.8
1
10.8 (opt )
1
10.8 (opt )
12.8
12.8
12.8
4.5
4.5
4.5
4.5
1
5.5 (opt )
1
5.5 (opt )
1
5.5 (opt )
1
5.5 (opt )
6.5
6.5
6.5
6.5
7.0
7.0
7.0
1
9.0 (opt )
1
9.0 (opt )
1
9.0 (opt )
11.0
11.0
9.1
9.1
1
11.1 (opt )
1
11.1 (opt )
13.1
9.0
9.0
1
11.0 (opt )
1
11.0 (opt )
13.0
7.9
1
9.6 (opt )
1
9.6 (opt )
1
9.6 (opt )
1
9.6 (opt )
11.0
11.0
13.0
Water Content
Before Test (%)
8.7
9.0
9.5
9.3
12.6
11.5
14.0
14.2
13.2
4.3
4.9
5.5
4.7
5.8
5.9
5.6
5.6
6.7
6.5
5.8
6.5
7.5
7.2
7.3
9.7
9.6
9.3
11.7
11.6
9.4
8.6
11.4
11.3
14.7
9.2
9.2
11.3
11.4
13.9
8.2
10.0
10.2
9.9
9.8
11.4
11.4
14.1
Water Content
Target Dry
Actual Dry
3
3
After Test (%) Density (kg/m ) Density (kg/m )
8.4
1741
1743
8.8
1801
1798
8.4
1833
1821
8.4
1833
1825
10.2
1741
1713
10.3
1833
1822
11.2
1741
1723
11.9
1822
1800
11.3
1833
1827
4.2
1903
1907
4.1
1903
1896
4.5
2003
1984
4.1
2003
1999
4.7
1903
1898
4.4
1903
1896
4.5
2003
2001
4.9
2003
2001
5.4
1903
1899
4.9
1903
1903
4.8
2003
2016
4.9
2003
2003
6.5
1850
1841
6.1
1850
1847
6.5
1916
1911
7.7
1916
1904
7.7
1916
1906
7.5
2022
2017
8.4
1916
1904
8.5
2022
2011
8.6
1808
1803
8.1
1884
1893
10.4
1808
1803
9.9
1884
1881
11.3
1884
1858
9.1
1813
1810
9.0
1867
1864
9.9
1867
1862
10.0
1961
1954
11.7
1961
1946
7.4
1841
1836
8.8
1901
1894
8.6
1901
1891
8.6
2028
2023
8.4
2028
2024
9.8
1987
1980
9.2
2028
2021
9.5
2028
2008
Note1 opt = optimum water content corresponding to the interpreted maximum dry density
59
2.10.2.2 Sample Preparation
Mr test samples were prepared in accordance with AASHTO T307. Each
sample was compacted using a vibratory hammer in a split mold with a target
diameter and height of 100 mm and 203.2 mm, respectively. A total of 47
samples were tested. The sample target water contents and dry densities are
shown in Table 2-8.
Steps to prepare the samples are as follows:
(1) Place a rubber membrane around the inside of the split mold with the aid
of a vacuum. Place the split mold around the bottom platen on a concrete
floor;
(2) Place a piece of filter paper on the top of the bottom platen;
(3) Add 1/6 of the required amount of moist aggregate into the split mold;
(4) Compact the aggregate using a vibratory hammer to the target depth;
(5) Repeat steps (3) and (4) 5 times until the desired total length of sample is
reached;
(6) Place a piece of filter paper and top platen on top of the compacted
sample;
(7) Apply a vacuum to the sample;
(8) Remove the split mold;
60
(9) Add a second membrane around the sample just in case the first
membrane was punctured during compaction;
(10) Place sample, membranes and end platens in a triaxial test chamber and
tighten the chamber tightly to the top and base of the triaxial cell using bolted
steel rods with end threads;
(11) Align the triaxial chamber in the loading frame;
(12) Apply the desired confining pressure;
(13) Remove sample vacuum; and
(14) Perform Mr testing.
Figures 2-24 and 2-25 show some of the materials tested and the compaction
apparatus, respectively.
61
Figure 2-24 Materials tested: RAP after Mr testing (top left), RG and VA blend
after Mr testing (top right), 100% RCA before (bottom left) and after (bottom
right) mixing with water but before Mr testing.
Figure 2-25 Sample preparation apparatus (left) and compaction density
control (right)
62
2.10.2.3 Mr Test Procedure and Equipment
The two recent Mr test procedures are AASHTO T307 and NCHRP 1-28A.
AASHTO T307 is less suited for weaker materials compared to NCHRP 128A. There are a total of 15 combinations of deviator and confining stresses
in AASHTO T307 while there are 30 in NCHRP 1-28A. The AASHTO T307
test procedure was adopted because of the following:
1.
the samples tested were not weak;
2.
AASHTO T307 requires a shorter testing time; and
3.
NCHRP 1-28A had not yet been adopted by AASHTO at the time
these tests were conducted.
There are three stages in the Mr test:
1) conditioning - all samples were subjected to 500 cycles of a deviator
stress of 95 kPa under a 105 kPa confining pressure to better simulate the
events occurring between compaction and traffic loading and to reduce the
effects of improper contact between the top platen and the specimen;
2) measuring stresses and strains to determine Mr – apply 100 cycles at
each combination of confining and deviator stresses. Mr is calculated as the
average of the ratios of the deviator stress to resilient strain for the 96 th
through 100th cycle; and
3) quick shear testing – shear the sample drained at a strain rate of 1%
per minute to measure the failure deviator stress.
63
All Mr tests were run using IPC Global Limited‘s Universal Testing System 25
(de Vos, 2004) consisting of a hydraulic axial stress and a pneumatic
confining stress loading systems, a computer-controlled data acquisition
system (CDAS) and a personal computer.
The CDAS provides both the
servo-feedback loading control electronics, and the transducer data
acquisition and timing functionality.
The testing software is the UTS009
Unbound Materials Resilient Modulus Test Software by IPC Global Limited.
The system is capable of applying repeated cycles of a haversine-shaped
load pulse of 0.1s with a 0.9s rest period. The system has two external
sample LVDTs that provide the sample deformation, and a system LVDT that
is attached to the actuator that provides the system deformation.
Deformations measured by the system LVDT are always larger than those
measured by sample LVDTs 1 and 2 since the system LVDT also measures
system compliance in addition to sample deformation.
Therefore, it is
important to use the sample LVDTs when computing the Mr.
Figure 2-26, 2-27 and 2-28 show a sample ready for testing and the LVDT
setup, the CDAS and a sample after Mr and quick shear testing, respectively.
64
Figure 2-26 Sample ready for testing (left) and the LVDT setup (right)
Figure 2-27 Computer-controlled data acquisition system
65
Figure 2-28 Sample after Mr and quick shear testing
Quality Control
Quality control on the following was made throughout the entire test program:
1) Dry density – The density should be within 3 percent of the target
density per AASHTO T307. All samples met this requirement (Table 2-8). The
critical measurement for controlling density is the sample volume since the
weight can be accurately determined with a scale. Sample heights in the split
mold were controlled using markings on the compaction rod (Figure 2-25).
The various taped marks correspond to the desired compacted lift heights.
2) Water content - The water content should be within 1 percent of the
target water content per AASHTO T307. The majority of the samples met this
66
requirement (Table 2-8). The water contents were measured before and after
testing. The values after testing were always smaller because drainage was
allowed during testing.
The difference is more significant for the wetter
samples.
3) Deformation measurements - The resilient deformation used for
calculating Mr is the average measured by LVDTs 1 and 2. Their ratios were
checked to see if they were within the range of 0.95 - 1.05. Satisfying this
ratio is an indication of minimal eccentric loading on the sample during
testing. All samples met this requirement.
2.10.3 FACTORS AFFECTING Mr
Observations on the various factors influencing Mr are reported in this section.
The reasonableness of these observations can be considered as part of the
quality control process.
2.10.3.1 Effect of Stress Level on Mr
The effect of confining and deviator stresses on the M r of VA is presented in
Figure 2-29a. Increases in both the confining and deviator stresses lead to
higher Mr. It was observed that the rate of increase in Mr with increasing
stress level is material specific (e.g., compare VA - Figure 2-29a with RG&VA
- Figure 2-29b).
One advantage of using bulk stress only instead of separately using confining
and deviator stresses in Mr models is its simplicity (only two parameters are
required in the K- model). Note that = d + 33. Therefore, the K- model
67
assumes that the effect of increasing the confining stress by one unit of stress
on Mr is identical to the effect of increasing the deviator stress by three units
of stress, which is not always true. This is the main disadvantage of using
bulk stress alone to model Mr.
2.10.3.2 Effect of Water Content on Mr
The effect of water content on Mr of VA is shown in Figure 2-30 for samples
having similar dry densities. As the water content increased, the stiffness
decreased for most materials, with only a few exceptions. Water content did
not have a strong influence on Mr of RAP. This may be attributable to the fact
that water content did not have a great effect on the compaction curve (Figure
2-23d).
68
400
20.7 kPa
34.5 kPa
68.9 kPa
Mr (MPa)
300
103.4 kPa
137.9 kPa
200
100
0
0
50
100
150
200
250
Deviator Stress (kPa)
Figure 2-29a Mr as a function of stress level - VA (Legend - confining stress)
400
20.7 kPa
34.5 kPa
68.9 kPa
Mr (MPa)
300
103.4 kPa
137.9 kPa
200
100
0
0
50
100
150
200
250
Deviator Stress (kPa)
Figure 2-29b Mr as a function of stress level - RG&VA (Legend - confining
stress)
69
500
9.3%/1825 kg/m3
400
11.5%/1822 kg/m3
Mr (MPa)
13.2%/1827 kg/m3
300
200
100
0
0
3
6
9
12
15
Loading Sequence No.
Figure 2-30 Effect of water content on Mr for VA (Legend - molding water
content/dry density)
2.10.3.3 Effect of Dry Density on Mr
In general, Mr increased with increasing dry density. Figure 2-31 shows the
effect of dry density on Mr of VA for samples having similar water contents.
For RAP, dry density had little influence on Mr.
70
400
14.0%/1723 kg/cm3
14.2%/1800 kg/cm3
Mr (MPa)
300
200
100
0
0
3
6
9
12
15
Loading Sequence No.
Figure 2-31 Effect of dry density on Mr for VA (Legend - molding water
content/dry density)
2.10.4 Mr MODELING
Regression analysis is used to develop a relationship between two or more
variables in such a way that one variable can be predicted by the other
variable(s). The predicted variable is called the dependent variable (M r in this
case) while the other parameters are known as independent variables. In this
research, ordinary least squares (OLS) regression analysis was performed
with the aid of statistical software SPSS Statistics GradPack version 17.0
distributed by SPSS (Statistical Package for the Social Sciences) Inc.
71
2.10.4.1 Mr Modeling of Individual Samples
To study the effects of confinement and shear on Mr, values of ki were first
estimated for each sample using the two-parameter model by Seed et al.
(1967) and the three-parameter model in the MEPDG (ARA, Inc. 2004).
(2.2)
(2.3)
where = bulk stress, oct = octahedral shear stress, pa = atmospheric
pressure and k1, k2, and k3 are regression parameters
The regression
constants k1 and k2 in Equation 2.2 are summarized in Table 2-9 along with
some descriptive statistics in Table 2-10. (Refer to Song, 2009 for detail plots
of the data). The regression constants k1, k2 and k3 in Equation 2.3 are also
summarized in Table 2-9 along with some descriptive statistics in Table 2-11.
The majority of the coefficients of determination, R2, range from 0.95 to 0.99
for both Equations 2.2 and 2.3. Overall, the R2 from Equation 2.3 is slightly
larger than those from Equation 2.2.
While there are some negative k3 values, they are mostly positive, indicating
that Mr increased with increasing octahedral shear stress.
One useful
exercise is to understand the effects of saturation or water content and void
ratio or dry density on ki.
These trends are useful when subsequently
developing the two- and three-parameter models for each material dataset.
72
Table 2-9 Summary of regression parameters for Equations 2.2 and 2.3
Target
Water
Actual Dry
Water Content
Density
Material
Content before
3
(kg/m )
(%)
Test(%)
VA
RAP
RAP
&VA
RCA
RCA
&VA
RG
&VA
8.8
8.8
8.8
8.8
10.8
10.8
12.8
12.8
12.8
4.5
4.5
4.5
4.5
5.5
5.5
5.5
5.5
6.5
6.5
6.5
6.5
7.0
7.0
7.0
9.0
9.0
9.0
11.0
11.0
9.1
9.1
11.1
11.1
13.1
9.0
9.0
11.0
11.0
13.0
7.9
9.6
9.6
9.6
9.6
11.0
11.0
13.0
8.7
9.0
9.5
9.3
12.6
11.5
14.0
14.2
13.2
4.3
4.9
5.5
4.7
5.8
5.9
5.6
5.6
6.7
6.5
5.8
6.5
7.5
7.2
7.3
9.7
9.6
9.3
11.7
11.6
9.4
8.6
11.4
11.3
14.7
9.2
9.2
11.3
11.4
13.9
8.2
10.0
10.2
9.9
9.8
11.4
11.4
14.1
1743
1798
1821
1825
1713
1822
1723
1800
1827
1907
1896
1984
1999
1898
1896
2001
2001
1899
1903
2016
2003
1841
1847
1911
1904
1906
2017
1904
2011
1803
1893
1803
1881
1858
1810
1864
1862
1954
1946
1836
1894
1891
2023
2024
1980
2021
2008
Equation 2.2
Equation 2.3
2
2
k1
k2
R
k1
k2
k3
R
0.98
1.25
0.69
1.30
0.58
0.97
0.64
0.67
0.70
1.73
1.33
1.58
1.43
1.54
1.69
1.87
1.69
1.48
1.83
1.48
1.81
1.58
1.44
1.40
1.13
1.21
1.18
0.95
0.84
1.45
1.72
1.17
1.29
0.88
1.28
0.81
0.86
0.95
0.52
0.66
0.66
0.71
0.68
0.76
0.57
0.66
0.56
0.68
0.50
0.83
0.54
0.85
0.61
0.75
0.82
0.80
0.52
0.68
0.50
0.50
0.59
0.53
0.50
0.53
0.58
0.51
0.62
0.52
0.59
0.59
0.58
0.58
0.67
0.78
0.73
0.95
0.55
0.60
0.71
0.67
0.63
0.59
0.72
0.73
0.74
1.00
0.89
0.74
0.80
0.86
0.85
0.90
0.88
0.89
0.994
0.906
0.982
0.986
0.990
0.939
0.992
0.992
0.995
0.991
0.982
0.904
0.906
0.992
0.990
0.974
0.987
0.973
0.990
0.980
0.995
0.970
0.992
0.967
0.980
0.989
0.987
0.975
0.988
0.991
0.967
0.990
0.965
0.949
0.980
0.979
0.990
0.998
0.956
0.991
0.971
0.976
0.954
0.992
0.990
0.993
0.958
0.98
1.12
0.64
1.24
0.55
0.87
0.62
0.64
0.68
1.71
1.32
1.41
1.26
1.53
1.66
1.78
1.64
1.39
1.83
1.41
1.81
1.62
1.49
1.34
1.08
1.25
1.20
0.90
0.86
1.43
1.60
1.21
1.18
0.79
1.28
0.77
0.83
0.95
0.50
0.67
0.62
0.66
0.62
0.76
0.57
0.66
0.52
0.68
0.29
0.69
0.46
0.76
0.40
0.68
0.73
0.75
0.50
0.67
0.28
0.28
0.57
0.49
0.41
0.47
0.46
0.51
0.53
0.52
0.64
0.65
0.50
0.48
0.73
0.81
0.60
1.00
0.52
0.45
0.76
0.51
0.43
0.58
0.61
0.67
0.75
0.93
0.90
0.61
0.66
0.65
0.84
0.90
0.89
0.75
0.02
0.79
0.52
0.32
0.32
0.82
0.30
0.35
0.19
0.11
0.05
0.88
0.87
0.04
0.13
0.35
0.24
0.45
0.00
0.99
0.00
-0.20
-0.22
0.31
0.38
-0.22
-0.11
0.47
-0.21
0.09
0.54
-0.21
0.63
0.79
0.03
0.43
0.22
-0.04
0.29
-0.05
0.47
0.51
0.77
0.04
-0.01
-0.03
0.54
0.994
0.978
0.994
0.996
0.994
0.992
0.997
0.997
0.996
0.993
0.982
0.985
0.987
0.992
0.992
0.989
0.993
0.990
0.990
0.989
0.995
0.974
0.997
0.975
0.992
0.992
0.989
0.987
0.989
0.992
0.990
0.993
0.990
0.992
0.980
0.980
0.993
0.998
0.959
0.991
0.986
0.991
0.984
0.992
0.990
0.993
0.967
73
Table 2-10 Summary of descriptive statistics for k1 and k2 in Equation 2.2
Material
Statistics
Mean
Standard deviation
VA
Coefficient of variation (CV)
Range
Mean
Standard deviation
RAP
Coefficient of variation (CV)
Range
Mean
Standard deviation
RAP&VA
Coefficient of variation (CV)
Range
Mean
Standard deviation
RCA
Coefficient of variation (CV)
Range
Mean
Standard deviation
RCA&VA
Coefficient of variation (CV)
Range
Mean
Standard deviation
RG&VA
Coefficient of variation (CV)
Range
74
k1
k2
0.86
0.27
0.31
0.64 -1.3
1.62
0.17
0.11
1.33 - 1.83
1.22
0.25
0.21
0.84 - 1.58
1.30
0.31
0.24
0.88 -1.72
0.88
0.27
0.31
0.52 -1.28
0.66
0.07
0.10
0.56 - 0.76
0.71
0.13
0.19
0.54 - 0.85
0.55
0.06
0.10
0.50 - 0.68
0.68
0.13
0.19
0.58 - 0.95
0.63
0.06
0.10
0.55 - 0.71
0.76
0.15
0.20
0.59 - 1.00
0.85
0.06
0.06
0.74 - 0.90
Table 2-11 Summary of descriptive statistics for k1, k2 and k3 in Equation 2.3
Material
Statistics
Mean
Standard deviation
VA
CV1
Range
Mean
Standard deviation
RAP
CV
Range
Mean
Standard deviation
RAP&VA
CV
Range
Mean
Standard deviation
RCA
CV
Range
Mean
Standard deviation
RCA&VA
CV
Range
Mean
Standard deviation
RG&VA
CV
Range
1 Coefficient of variation
k1
k2
k3
0.82
0.25
0.30
0.55 - 1.12
1.56
0.20
0.13
1.26 - 1.83
1.22
0.27
0.22
0.86 - 1.62
1.24
0.31
0.25
0.79 - 1.60
0.87
0.28
0.33
0.50 - 1.28
0.64
0.07
0.11
0.52 - 0.76
0.60
0.17
0.29
0.29 - 0.75
0.47
0.11
0.23
0.28 - 0.67
0.68
0.17
0.25
0.48 - 1.00
0.53
0.13
0.25
0.43 - 0.76
0.71
0.14
0.20
0.58 - 0.93
0.78
0.12
0.16
0.61 - 0.90
0.40
0.26
0.65
0.02 - 0.82
0.34
0.37
1.08
0.00 - 0.88
0.03
0.30
12.18
(-0.22) - 0.47
0.37
0.41
1.13
(-0.21) - 0.79
0.19
0.19
1.03
(-0.04) - 0.43
0.28
0.33
1.16
(-0.05) - 0.77
75
2.10.4.2 Two-Parameter Mr Modeling for Each Material Dataset
In Equation 2.2, Mr is expressed as a function of only the sample bulk stress.
Mr can also be made a function of the sample water content and dry density
by incorporating these parameters in k1 and k2. Several models have been
developed using this idea where the water content (or saturation) and dry
density (or void ratio) are referenced to the values at optimum (e.g., Ooi et al.,
2004 and Archilla et al., 2007). With the test gradation however, an optimum
value was not reached in 4 of the 6 compaction curves. Since the optimum
only serves as a reference point, it is conceivable that the referencing can be
made with respect to the zero air void (ZAV) curve instead.
Archilla et al. (2007) found that saturation and void ratio provided better
correlation with resilient modulus than water content and dry density. Hence,
k1 and k2 are expressed in terms of Szav - S and e - ezav as follows:
k1 = a1(Szav - S) + a2(e - ezav) + a3
k2 = b1(Szav - S) + b2(e - ezav) + b3
(2.4)
where S = degree of saturation of sample, Szav = degree of saturation on the
ZAV curve at the same dry density as the sample = 1, e = sample void ratio,
ezav = void ratio on the ZAV curve at the same water content as the sample,
and, a1, a2, a3, b1, b2 and b3 are regression constants.
Figure 2-32 illustrates the relationship between the parameters Szav - S and e
- ezav and the ZAV curve. Table 2-12 presents sample calculations for Szav - S
and e - ezav for VA.
76
Dry Unit Weight
Zero Air Void Curve
y
x
Water Content
Figure 2-32 Szav - S is related to x and e - ezav is related to y
Table 2-12 Sample calculation of Szav - S and e - ezav for VA.
w
d
e=Gsw/d-1 ezav=wGs e - ezav S=wGs/e Szav - S
(%)
(kN/m3)
8.7%
17.1
0.64
0.25
0.39
0.39
0.61
9.0%
17.6
0.59
0.26
0.33
0.44
0.56
9.5%
17.9
0.56
0.27
0.29
0.48
0.52
9.3%
17.9
0.56
0.27
0.30
0.47
0.53
12.6%
16.8
0.66
0.36
0.30
0.54
0.46
11.5%
17.9
0.56
0.33
0.24
0.58
0.42
14.0%
16.9
0.65
0.40
0.26
0.61
0.39
14.2%
17.7
0.58
0.40
0.18
0.69
0.31
13.2%
17.9
0.56
0.38
0.18
0.67
0.33
Regression constants for VA are summarized in Table 2-13. The t-statistic for
parameter b1 was smaller than 2.0, indicating that b1 is statistically
insignificant.
Hence it is not included in the table. Even though the t-statistic
77
for parameter b3 is less than 2.0, it was not and should not be excluded. This
is because excluding constants is likely to introduce a bias to the model.
Table 2-13 Regression results for VA using equations 4.2 and 4.4
95% Confidence Interval
Parameter Estimate Std. Error t-statistics
Lower Bound Upper Bound
a1
2.68
0.37
7.28
1.95
3.40
a2
-5.59
0.67
8.33
-6.91
-4.26
a3
1.20
0.15
8.20
0.91
1.49
b2
2.06
0.39
5.26
1.28
2.83
b3
0.10
0.11
0.91
-0.12
0.32
2
R =0.89
Figure 2-33 shows a plot of the measured and predicted Mr for VA using
equations 2.2 and 2.4. It can be seen that the correlation is quite good (R2 =
0.92). For other materials, the regression constants are shown in Table 2-14.
600
Mr pre. vs Mr mea.
80% Mr measured
Mr predicted (MPa)
500
120% Mr measured
y = 0.99x
R2 = 0.92
400
300
200
100
0
0
100
200
300
400
Mr measured (MPa)
500
600
Figure 2-33 Measured and predicted Mr for VA using equations 2.2 and 2.4
78
Table 2-14 presents a summary of parameter estimates, t-statistics and R2 for
all materials tested. Except for the blends [RCA&VA (R2 = 0.83), and RG&VA
(R2 = 0.84)], other materials had R2 larger than or close to 0.90.
79
Table 2-14 Summary of parameter estimates, t-statistics and R2 for two-parameter Mr model using equations 2.2 and 2.4
VA
RCA
RCA&VA
RAP
RAP&VA
RG&VA
Parameter Estimate t-stats Estimate t-stats Estimate t-stats Estimate t-stats Estimate t-stats Estimate t-stats
a1
2.68
7.28
7.53
13.95
1.34
4.18
-0.51 3.27
0.88
3.28
4.58
5.88
1
1
1
a2
-5.59
8.33
-8.40
10.07
-5.69
3.29
a3
1.20
8.20
0.02
0.192
0.36
3.09
1.88 19.62 0.91
8.06 0.002 0.042
1
1
b1
-0.80
4.91
-0.55
2.02
-0.37
2.45 -1.60
5.20
1
1
1
1
1
b2
2.06
5.26
b3
0.10
0.912
1.01
13.19
0.94
8.06
0.56 42.02 0.80 11.94 1.36
12.37
2
R
0.89
0.96
0.83
0.93
0.90
0.84
# of points
144
80
96
193
128
112
Note 1) When parameter estimates are not shown, it is because their t-statistics are less than 2.0 (not statistically significant). In this case, the
models were re-estimated by omitting these statistically insignificant parameters.
2) Parameter estimates a3 and b3 were not excluded even when their t-statistics were less than 2.0, because eliminating them may result
in a bias on k1 and k2.
80
Archilla et al. (2007) stated that a good model should have the following
characteristics: (1) intuitively correct signs (i.e.; Mr increases with decreasing
saturation, decreasing void ratio and increasing bulk stress); (2) parameters
must be statistically significant at a prescribed confidence level (i.e.; tstatistics ≥ 2.0 for a 95% confidence level); (3) fitted model should satisfy the
assumptions on which it is based; and (4) model should fit the data points well
(i.e.; large R2). These aspects were checked and found to be satisfied.
The two-parameter model can be easily extended to incorporate the percent
recycled material (i.e.; %RCA or %RAP) using the results for 0% recycled
material (i.e.; 100% VA), 50% blend and 100% recycled material.
To
accomplish this, the expressions for k1 and k2 are modified as follows:
k1 = a1(Szav - S) + a2(e - ezav) + a3 (%R) + a4
k2 = b1(Szav - S) + b2(e - ezav) + b3 (%R) + b4
(2.5)
where %R = percent recycled material, a1, a2, a3, a4, b1, b2, b3, and b4 are
regression constants.
Again, some parameters are not statistically significant (t-statistics less than
2.0). After excluding them in a step-wise fashion, the regression parameters
were re-estimated for RCA/VA blends and RAP/VA blends as summarized in
Tables 2-15 and 2-16, respectively.
Overall, the fit is quite good with
coefficients of determination of 0.89 for RCA blends and 0.92 for RAP blends.
The signs were also checked to see if the trends are sensible. With these
models, Mr increases with decreasing saturation, decreasing void ratio,
81
increasing bulk stress, increasing RAP content and increasing RCA content.
It is quite surprising that Mr increases with increasing RAP content but this is
probably due to: (1) RAP is made of Type A basalt; and (2) the water contents
at which the RAP and RAP blend were tested are significantly lower than VA.
Table 2-15 Summary of regression constants of RCA and VA blends using
equations 2.2 and 2.5
95% Confidence Interval
Std.
Parameter Estimate
t-statistics
Error
Lower Bound Upper Bound
a1
3.56
0.34
2.88
4.23
10.37
a2
-3.35
0.48
-4.29
-2.42
7.04
a3
0.28
0.02
0.23
0.32
11.93
a4
0.15
0.07
0.01
0.29
2.07
b1
-0.42
0.13
-0.68
-0.15
3.12
b4
0.88
0.06
0.75
14.01
R2 = 0.89, # of points = 320
1.00
Table 2-16 Summary of regression constants of RAP and VA blends using
equations 2.2 and 2.5
95% Confidence Interval
tParameter Estimate Std. Error
statistics Lower Bound Upper Bound
a1
a3
a4
b1
b2
b4
0.89
0.14
6.41
0.62
1.16
0.67
0.04
18.14
0.60
0.74
0.45
0.07
6.88
0.32
0.58
-0.89
0.10
9.09
-1.08
-0.70
0.72
0.16
4.58
0.41
1.03
0.92
0.04
20.84
0.83
1.00
2
R =0.92, # of points = 464
82
2.10.4.3 Three-Parameter Mr Modeling for Each Material Dataset
The same methodology used to develop the two-parameter models was
employed to develop the three-parameter models. Using OLS regression,
Equation 2.3 was combined with the following expressions for k1, k2 and k3:
k1 = a1(Szav - S) + a2(e - ezav) + a3
k2 = b1(Szav - S) + b2(e - ezav) + b3
(2.6)
k3 = c1(Szav - S) + c2(e - ezav) + c3
where S, Szav, e and ezav have been defined previously and a1, a2, a3, b1, b2,
b3, c1, c2 and c3 are regression constants.
Regression results for VA using equations 2.3 and 2.6 are summarized in
Table 2-17. The majority of the t-statistics are larger than 2.0, with c3 being
the only exception.
Figure 2-34 shows a plot of the predicted versus
measured Mr of VA using equations 2.3 and 2.6. For other materials, the
regression constants and t-statistics are contained in Table 2-18. Except for
an R2 of 0.84 for RCA&VA, all other materials showed R2 larger than 0.90.
Table 2-17 Regression results for VA using Equations 2.3 and 2.6
95% Confidence Interval
tParameter Estimate Std. Error
Lower
Upper
statistics
Bound
Bound
a1
5.53
0.61
9.03
4.32
6.75
a2
-6.99
0.94
7.45
-8.85
-5.14
a3
0.19
0.09
2.19
0.02
0.37
b1
-4.15
0.90
4.62
-5.93
-2.38
b2
5.79
1.39
4.16
3.04
8.54
b3
0.91
0.13
7.18
0.66
1.16
c1
4.37
2.02
2.16
0.36
8.37
c2
-6.68
3.14
2.13
-12.89
-0.47
c3
0.25
0.28
0.91
-0.29
0.80
2
R =0.96
83
500
400
Mr pre. vs Mr mea.
y = 0.99x
80% Mr measured
R = 0.96
2
M r predicted (MPa)
120 % Mr measured
300
200
100
0
0
100
200
300
400
500
M r measured (MPa)
Figure 2-34 Measured and predicted Mr for VA using equations 4.3 and 4.6
84
Table 2-18 Summary of parameter estimates, t-statistics and R2 for three-parameter Mr model using equations 2.3 and 2.6
Parameter
VA
Estimate t-stats
RCA
Estimate t-stats
RCA&VA
Estimate t-stats
RAP&VA
Estimate t-stats
a1
5.53
9.03
5.87
6.26
1.23
a2
-6.99
7.45
-5.47
3.27
1
a3
0.19
2.19
0.03
0.522
0.39
3.09
1
1
-0.37
1
1
b1
-4.15
4.62
-2.21
b2
5.79
4.16
3.51
2.86
1
b3
0.91
7.18
0.68
7.09
0.63
c1
4.37
2.16
5.99
3.50
-1.26
c2
-6.68
2.13
-13.45
4.59
1
c3
0.25
0.912
0.91
4.02
0.78
R2
# of points
0.96
144
0.98
80
4.51
RAP
Estimate t-stats
4.02
9.85
6.10
2.92
0.84
96
-5.19
5.98
0.88
8.48
5.85
1
2.80
10.77
0.91
0.49
3.26
RG&VA
Estimate t-stats
1
1
8.03
0.67
2.44
1
25.86
1
27.58
0.80
0.76
20.35
4.05
1
2.81
2.36
-7.56
4.40
1
-5.57
2.36
-0.60
1.932
-0.01
0.11
0.932
4.18
0.95
193
0.90
128
10.99
0.122
0.94
112
Note 1) When parameter estimates are not shown, it is because their t-statistics are less than 2.0 (not statistically significant). In this case, the
models were re-estimated by omitting these statistically insignificant parameters.
2) Parameter estimates a3, b3 and c3 were not excluded even when their t-statistics were less than 2.0, because omitting them may result
in a bias on k1 k2, and k3.
85
The three-parameter model can be easily extended to incorporate the percent
recycled material (i.e.; %RCA or %RAP) using the results for 0% recycled
material (i.e.; 100% VA), 50% blend and 100% recycled material.
To
accomplish this, the expressions for k1, k2 and k3 are expressed as follows:
k1 = a1(Szav - S) + a2 (e - ezav) + a3 (%R) + a4
k2 = b1(Szav - S) + b2 (e - ezav) + b3 (%R) + b4
(2.7)
k3 = c1(Szav - S) + c2 (e - ezav) + c3 (%R) + c4
where %R = percent recycled material as defined previously and a1, a2, a3, a4,
b1, b2, b3, b4, c1, c2, c3 and c4 are regression constants.
The regression constants for RCA and VA blends, and RAP and VA blends
are summarized in Tables 2-19 and 2-20, respectively.
Parameters with
absolute t-statistic values less than 2.0 were omitted unless they are constants.
For RCA and VA, the t-statistic for b3 was slightly less than 2 but was left in the
model.
Table 2-19 Summary of regression constants for RCA and VA blends using
equations 2.3 and 2.7
95% Confidence Interval
Parameter Estimate Std. Error t-statistics
Lower Bound Upper Bound
a1
a2
a3
a4
b1
b3
b4
c4
3.58
-3.43
0.18
0.18
-0.42
0.07
0.73
0.36
0.32
11.34
2.96
0.44
7.71
-4.31
0.05
3.46
0.08
0.07
2.55
0.04
0.12
3.40
-0.67
0.03
1.91
0.00
0.07
11.10
0.60
0.06
6.21
0.25
2
R =0.91, # of points = 320
86
4.20
-2.56
0.28
0.32
-0.18
0.13
0.86
0.47
Table 2-20 Summary of regression results for RAP and VA blends using
equations 2.3 and 2.7
95% Confidence Interval
Parameter Estimate Std. Error t-statistics
Lower Bound Upper Bound
a1
2.82
0.44
6.48
1.97
3.68
a2
-3.75
0.76
4.96
-5.23
-2.26
a3
0.33
0.11
2.92
0.11
0.54
a4
0.49
0.06
8.34
0.37
0.60
b1
-3.19
0.54
5.90
-4.25
-2.12
b2
4.78
0.96
4.97
2.89
6.67
b3
0.49
0.13
3.64
0.23
0.76
b4
0.83
0.07
11.71
0.69
0.97
c1
4.50
1.34
3.37
1.87
7.13
c2
-7.41
2.40
3.08
-12.13
-2.68
c3
-1.17
0.33
3.50
-1.82
-0.51
c4
0.28
0.17
1.67
-0.05
0.60
2
R =0.93, # of points = 464
In general, the three-parameter model yielded higher R2, while the twoparameter model has the advantage of being simpler and easier to apply. In
addition, the predicted Mr using both the two- and three-parameter models
generally falls within 80% to 120% of the measured values, indicative of a
good predictive capability.
2.10.5 SUMMARY AND CONCLUSIONS
Mr tests were performed on VA, RAP, RCA, 50% RAP:50% VA, 50%
RCA:50% VA, and 30% RG:70% VA, all having gradations that are close to
HDOT‘s base course gradation requirements. Models that incorporate the
effects of degree of saturation, void ratio, stress state and percent recycled
material content were presented. The following findings and conclusions are
offered:
The Mr samples mostly conformed to HDOT‘s base course gradation
except that they contained no fines. This is because of a lack of fines
87
in the samples (especially RAP) and as such, large amounts of
recycled materials had to be collected in order to collect the required
amount of fines. Possibly as a result, several of the materials tested
do not exhibit the classical bell-shaped compaction curve.
For the samples tested, Mr increased with increasing confining stress,
increasing deviator stress, increasing bulk stress, decreasing water
content and increasing density. Mr of RAP is relatively insensitive to
changes in water content and dry density because the compaction
curve was relatively flat to begin with.
The Mr of the recycled materials tested is comparable to or even higher
than that of the virgin aggregate.
Two- and three- parameter models capable of incorporating the effects
of saturation, void ratio, stress level and percent recycled material
were developed. The majority of the predicted Mr fell within 80% to
120% of the measured values. It should be noted that these models
were developed for the gradation tested. Even though Croney and
Croney (1997) indicated that the grading has little influence on the
modulus of crushed rock and crushed gravel, the applicability of these
models to other gradations should be verified.
In general, the three-parameter model yielded a higher R2, but the twoparameter model has the advantage of being simpler and easier to
apply.
88
2.11 PERMANENT DEFORMATION TEST AND SHAKEDOWN ANALYSIS
In this section, the following are presented: (1) a literature review on
permanent deformation (PD); (2) PD test results for a virgin basaltic
aggregate and three recycled materials using single- and multi-stage
repeated load triaxial (RLT) tests; (3) models developed to capture the
behavior of the tested materials in single-stage PD tests; and (4) the rationale
and procedure for evaluating the results of a multi-stage PD test.
In single-stage PD testing, multiple samples are compacted to the same
physical state and tested under the same confining pressure.
Only one
deviator stress is applied per sample but the deviator stresses vary from
sample to sample. In a multi-stage PD test, only one sample is tested at a
constant confining pressure. This sample is subjected to several deviator
stresses increasing stepwise from low to high until it fails or collapses. A
constant limited number of cycles (e.g., 1000) of each deviator stress is
applied to the sample.
Currently, there is no published procedure for
determining the shakedown (border between acceptable and unacceptable
behavior) limit from a multi-stage PD test. A procedure to identify the material
shakedown limit in a multi-stage PD test is proposed. This procedure is then
used to compare with results from single-stage PD testing to verify its
predictive capability.
2.11.1 LITERATURE REVIEW
PD or rutting of the wearing, base and subbase courses is an important
failure criterion that must be considered in pavement design.
89
Rutting of
unbound base and subbase layers (UBL) is directly incorporated in the new
Mechanistic-Empirical Pavement Design Guide or MEPDG (ARA, Inc. 2004).
One way to analyze rutting is to use the concepts of shakedown theory.
Shakedown analysis was first applied to pavements by Sharp and Booker
(1984). When the applied traffic-induced stress is below a certain threshold
known as the shakedown limit, the material‘s PD stabilizes to a constant
value with increasing load cycles. This represents a safe regime of applied
loading.
When the applied traffic load exceeds the shakedown limit, the
deformation increases rapidly with increasing load cycles and eventually,
leading to failure. Therefore, in shakedown limit-based rutting design, the
applied stress must be smaller than the material shakedown limit, deduced
from RLT testing.
Several studies have been previously performed on the PD behavior of RCA
and RAP.
These are summarized in Table 2-21.
characteristics of RG was found.
90
No study on the PD
Table 2-21 Recent PD studies on RCA and RAP
Recycled
Materials
Reference
Country
Highlights from Study
Tested
Gradation and composition of the granular
base are of secondary importance when
compared to the influence of the stress
Van Niekerk
conditions, water content and degree of
Netherlands RCA
et al. (2000)
compaction.
Aurstad and
Norway
Hoff (2002)
Mohammad
USA
et al. (2006)
Aurstad et
al. (2006)
Norway
Huurman
and
Molenaar
(2006)
Netherlands
Saeed
(2008)
USA
Good-quality road bases can be built using
RCA.
Recycled materials show high PD
RCA and resistance; RCA enjoys little improvement
RAP upon compaction, while the benefit of
compacting RAP is more significant.
RAP
RAP shows similar PD resistance as
crushed limestone.
RCA
Friction angles were higher than virgin
aggregate. RCA shows high stability and
PD resistance.
RCA
Shakedown limit of RCA and crushed
masonry depends largely on degree of
compaction.
PD resistance of RAP blends decrease with
RCA and
increasing %RAP; RCA and its blend is
RAP
superior to RAP and its blend.
A literature review on PD and shakedown behavior of unbound granular
materials (UGM) is summarized under the following general topics:
Consideration of PD of UGM in pavement design (Section 2.11.1.1)
Shakedown theory (Section 2.11.1.2)
Factors affecting PD of UGM (Section 2.11.1.3)
91
Modeling PD behavior and shakedown analysis (Section 2.11.1.4)
Previously, PD was controlled by limiting the applied stress in the UGM to an
arbitrary fraction of the failure deviator stress. This limiting applied shear
stress ratio is defined in Figure 2-35. A typical value of 0.7 was common in
England (Brown and Dawson, 1992) and South Africa (Almássy, 2002).
According to Tutumluer and Dawson (2004), this limiting value ranges
between 0.6 and 0.7. For wet aggregate with fines (e.g. during spring thaw),
Dawson et al. (2007) suggested that this limiting value should be lowered to
0.5 to 0.55 based on RLT testing. Shakedown limit analysis provides a more
rational method of establishing the limiting applied shear stress and is
discussed in Section 2.11.1.2.
92
1
f f
45+/2
3
max
f
c
3
f
Shear Stress Ratio:
1
Applied Shear Stress (f)
Shear Strength (max)
Figure 2-35 Schematic illustration of shear stress ratio criterion in pavement
design (Tutumluer and Dawson, 2004)
2.11.1.1 Consideration of PD of UGM in Pavement Design
Stresses induced in a pavement system due to traffic loading are highest in
the upper layers and diminish with depth (Figure 2-36). Consequently, higher
quality and generally more expensive materials (base course) are used in the
highly stressed upper layers, and lower quality and less expensive materials
(subbase course) are used in the deeper layers of the pavement. This
optimization of material usage minimizes construction costs (Christopher et
al., 2006).
93
Figure 2-36 Attenuation of traffic induced stresses with depth (Christopher et
al., 2006)
To study rutting, it is important to understand the stresses in pavement layers.
2.11.1.1.1 Stresses in Pavement UGM
Acting on a given element in a UGM are a set of complementary normal and
shear stresses. It can be shown that for a given state of stress at a point,
there are three mutually perpendicular planes known as principal planes on
which the shear stresses are zero. Acting on these principal planes is a set of
three principal stresses.
A moving wheel load imposes varying magnitudes of vertical, horizontal, and
shear stresses in the UGM at different times.
As traffic approaches and
passes over a given point, rotation of principal stresses occurs as shown in
Figure 2-37. A description of what a geomaterial element experiences as a
wheel load approaches and passes is as follows:
94
First, the applied vertical stress is lower than the applied horizontal
stress when the wheel is far from the element.
Second, the applied vertical stress becomes higher than the applied
horizontal stress, when the wheel approaches the element.
Third, the applied vertical and horizontal stresses reach their highest
values when the wheel is right above the element. The applied vertical
stress is still higher than the applied horizontal stress. Only during this
instant are the vertical and horizontal stresses the major and minor
principal stresses, respectively.
The fourth and fifth scenarios are analogous to the second and first
scenarios, respectively, as the wheel leaves the element.
95
Figure 2-37 Stresses beneath rolling wheel load (Lekarp et al., 2000)
During traffic loading, the stresses consist of static and dynamic stress
components. Static components of stress are attributable to self-weight and
locked-in stresses induced during compaction and initial traffic loading. The
dynamic stress component is due to traffic loading. It is common practice
among pavement engineers to preclude the locked-in compaction-induced
stresses. Figure 2-38 presents a series of load-unload-reload paths that can
occur during compaction and initial trafficking, where v' and h' are vertical
and horizontal effective stress, respectively.
96
Figure 2-38 Field stresses during a load-unload-reload path (redrawn after
Mayne and Kulhawy, 1982)
Arnold (2004) noticed the significance of locked-in lateral stress on pavement
design and summarized previous research by Sowers et al. (1957); Uzan
(1985); Selig (1987); Duncan and Seed (1986); and Almeida (1993). Selig
(1987) found large lateral plastic strains at the bottom of a pavement granular
layer during initial loading with the response rapidly approaching an elastic
condition with subsequent loading. This suggests that tensile stresses occur
in the first few cycles but are quickly cancelled out by the developed lateral
locked-in stresses, resulting in a net horizontal compressive stress state.
Selig concluded that the locked-in lateral stress is the most important factor
limiting rutting of granular base, and suggested (as well as by Uzan, 1985)
that it should be considered in mechanistic-based pavement design.
97
The at-rest coefficient of lateral earth pressure during virgin loading is related
to the soil friction angle, , as follows (Jaky, 1944):
Ko = 1 – sin
(2.8)
Equation 2.8 can be confirmed in the laboratory using a consolidometer that
has the ability to measure lateral stress or a triaxial apparatus by measuring
the lateral to vertical stress ratio when the axial and volumetric strains are
equal. The value of Ko for normal consolidation should be distinguished from
overconsolidation. For primary or first unloading as shown in Figure 2-38, Ko
can be expressed as (Kulhawy and Mayne 1990)
Ko = (1- sin)OCR sin
(2.9)
where
'
OCR = overconsolidation ratio = vm
/ v'
'
= maximum past or preconsolidation pressure
vm
v' = current vertical effective stress.
Assuming the preconsolidation pressure remains unchanged, values of Ko for
subsequent reload and unload cycles will be less than those during primary
unloading.
Typically, bases and subbases are compacted during the pavement
construction process, rendering these layers overconsolidated. However, it is
98
difficult to estimate the OCR during design because the compactive effort (or
equipment) is seldom known until construction. As a result, the actual lockedin horizontal stress remains elusive to pavement engineers and is often
estimated as (1 - sin) v' , which is the value for virgin loading. Ignoring these
locked-in stresses can have an impact on the pavement design.
2.11.1.1.1 Behavior of UGM in a PD Test
Fig. 2-39 presents a typical load-unload stress-strain cycle for a UGM. It is
not retraceable upon removal of load. Instead, a hysteresis loop is formed.
Two different strains are observed in this cycle: a resilient strain, which is
recoverable after the load is removed, and a permanent or plastic strain,
which can accumulate with additional load cycles.
This permanent strain
must be limited in design of pavements against rutting.
Permanent
Stress Strain
Resilient
Strain
Strain
Figure 2-39 Hysteresis loop during a load-unload cycle in a RLT test on UGM
99
Based on Hertz contact theory, Werkmeister (2003) postulated that the
resilient deformation is mainly attributable to the deformation of the individual
grains. On the other hand, permanent deformation is primarily due to particle
re-orientation. Mechanisms such as particle rotation and sliding play a big
role during traffic loading. The most severe loading however, occurs during
compaction, when particles can crush or grains can abrade. Consequently,
grain fragmentation is more important during compaction and less during the
service life of the pavement.
In the laboratory, PD is commonly measured using the constant confining
pressure (CCP) RLT test. In this test, the stresses applied only mimic the in
situ principal stresses directly beneath the center of the wheel load. It is
unable to simulate rotation of principal stresses and the shear stresses
induced during real traffic loading.
In reality, the confining stress is not
constant as in the CCP RLT test, but rather it is variable. More flexible stress
paths can be simulated by using devices such as the FastCell, developed at
the University of Illinois at Urbana-Champaign, a hollow cylinder apparatus
(Chan, 1990) or a K-mold apparatus (Arnold, 2004).
Applying a variable
confining pressure (VCP) best mimics the conditions in the field. However,
these are more expensive and difficult to perform and are used mostly as
research tools.
100
2.11.1.1.2 Consideration of PD in Pavement Design
Rutting occurs not only in the wearing course but also in the unbound layers.
For example, at the American Association of State Highway Officials
(AASHO) road test in Ottawa, IL conducted between 1958 and 1960, the AC,
base, subbase, and subgrade layers contributed 32%, 18%, 39%, and 11%,
respectively, to the total rut depth (Christopher et al., 2006); i.e., about twothirds of the rutting was in the unbound materials.
In the Canterbury
Accelerated Pavement Testing Indoor Facility (CAPTIF) pavement in
Christchurch, New Zealand, the base layer contributed up to 70% of the total
rut depth (Haddock et al., 2005).
Quite often used in the United States, the 1993 AASHTO method for
pavement design is based on the full scale AASHO road test. In this method,
rutting in unbound materials is related empirically to the elastic or resilient
strain at the top of the subgrade (Christopher et al., 2006). As Monismith
(2004) and Dawson et al. (2008) criticized, this method is based on a set of
specific local environmental conditions and cannot be applied elsewhere as a
“one-for-all principal”.
In the MEPDG (ARA, Inc., 2004) approach, pavement design is accomplished
by inputting the traffic load spectra, material properties and thickness, and
environmental conditions. The MEPDG software performs a mechanistic
analysis of the pavement and outputs stresses and strains. Then empirical
relationships are used to relate the outputs to pavement distresses. The
MEPDG software calculates the PD of each layer by subdividing them into
small elements and then summing the total rut depth. It characterizes the PD
101
of unbound base, subbase, and subgrade materials using the Tseng and
Lytton (1989) model (discussed later).
2.11.1.2 Shakedown Theory
Shakedown theory was originally developed to analyze the behavior of
pressure vessels under cyclic thermal loads, and later metal surfaces under
repeated rolling or sliding loads (Werkmeister, 2003). It has been used to
describe the behavior of structures and more recently pavements under cyclic
loading.
Two factors that influence material response to repeated loading are the
stress levels and number of load applications (Dawson, 1999; Theyse, 2000;
Khogali et al., 2007; Yang et al., 2008). At low levels of deviator stress, the
deformation reaches an asymptotic value and becomes resilient as the
number of cycles becomes very large. At high levels of deviator stress, PD
continuously increases eventually leading to failure or collapse. This implies
a critical stress level between stable and unstable conditions must exist. This
critical stress level is termed the plastic shakedown limit.
According to Werkmeister (2003), a material‘s PD behavior can be
categorized into one of the following three ranges as shown in Figure 2-40
and Figure 2-41:
Range A Applied load is smaller than the plastic shakedown limit, and the PD
approaches a constant value with increasing number of load cycles. The
102
response then becomes entirely resilient.
This behavior is termed plastic
shakedown.
Range C Applied load is large and the sample fails quickly at low number of
cycles. The deformation is predominantly plastic.
Known as incremental
collapse, this is an undesirable situation and should be avoided in pavement
design.
Range B Applied load is larger than the plastic shakedown limit but is smaller
than the plastic creep limit, which is the limit between incremental collapse
and this intermediate behavior. A material in this range, also known as plastic
creep, will eventually fail at a large number of load cycles.
Figure 2-40 Shakedown ranges (Tutumluer and Dawson, 2004)
103
Figure 2-41 Shakedown behavior for UGM (Werkmeister, 2003)
The three different ranges can be distinguished by plotting the results as
follows:
1) vertical permanent strain versus number of load cycles (Figure 2-40)
2) vertical permanent strain rate (vertical permanent strain divided by
number of load cycles) on a log scale versus vertical permanent strain (Figure
2-42)
3) resilient
strain
versus number of
load cycles
(Figure
2-43).
Alternatively, the resilient modulus could be plotted instead of resilient strain
as the two are inversely related.
A description of how the behavioral ranges are distinguished is summarized
in Table 2-22. The least ambiguous procedure to distinguish between the
104
three behavioral ranges is the permanent strain rate versus permanent strain
plot.
Figure 2-42 PD ranges by permanent strain rate (Werkmeister et al., 2004)
Figure 2-43 PD ranges by resilient strain (Werkmeister et al., 2004)
105
Table 2-22 Methods for distinguishing the various PD behavioral ranges
Plot
Permanent
strain versus
number of
cycles
(Figure 2-40)
Range A
(Shakedown)
Range B
(Plastic Creep)
Permanent
strain
approaches a
constant value
after a large
number of load
cycles
Permanent strain
appears to approach a
constant value but
eventually increases
asymptotically after a
large number of load
cycles; the latter may
not be observed in a PD
test with a limited
number of cycles
Resilient
Resilient
Slight decrease in
modulus
modulus initially resilient modulus
versus
increases
(modulus softening) with
number of
(modulus
increasing number of
cycles
hardening) but cycles
(Figure 2-42) approaches a
constant after a
large number of
cycles
Permanent Permanent
Permanent strain rate
strain rate
strain rate
decreases linearly at
versus
decreases
first with increasing
permanent linearly with
permanent strain
strain
increasing
followed by a flattening
(Figure 2-43) permanent strain of the curve
Range C
(Incremental Collapse)
Permanent strain
increases asymptotically
after a relatively low
number of load cycles
Large decrease in
resilient modulus
(modulus softening) with
increasing number of
cycles
Permanent strain rate
decreases very slowly or
not at all with increasing
permanent strain or the
permanent strain rate
decreases with
permanent strain
followed by an increase
2.11.1.3 Factors affecting PD of UGM
Factors that can decrease a geomaterial‘s susceptibility to PD include
(Lekarp et al., 2000; Dawson et al., 2000 and Cheung and Dawson, 2002):
1. higher relative density
2. lower water content or higher suction
3. higher preconsolidation pressure
4. higher confining stress
5. lower applied stress
106
6. smaller number of load cycles
7. more well-graded as opposed to a uniform gradation
8. lower fines content
9. more angular and rough particles as opposed to rounded and smooth
10. larger maximum particle size
2.11.1.4 Permanent Deformation Models
One objective of this research is to develop models to predict the PD at any
number of cycles under a given stress level. The PD models available can be
classified into three categories: (1) Models that relate permanent strain to
number of cycles only (Table 2-23); (2) Models that relate permanent strain to
stress level only (Table 2-24); (3) Models that relate permanent strain to both
number of cycles and stress levels (Table 2-25).
Table 2-23 Models for estimating permanent strain as a function of the
number of load cycles (modified after Hornych and El Abd, 2004)
107
Table 2-24 Models for estimating permanent strain as a function of the
applied stress level (modified after Hornych and El Abd, 2004)
108
Table 2-25 Models for estimating permanent strain as a function of the
number of load cycles and applied stress level
Author
Parameters
Relationship
sp
Pappin
(1979)
q
p
sp f n N L
permanent shear strain
fn(N) shape function, depending
on the number of cycles N,
p mean normal stress
2.8
L
p2 q2
0.95S axial strain at 95% of the
Lentz and
Baladi
(1981)
n( q / S )
ln( N )
1 m(q / S )
1p 0.95S ln(1 q / S ) 0.15
deviator stress at failure,
n model parameter
m slope of the failure line
S deviator stress at failure
N number of loading cycles
Note: this model is based on
static load testing
1p permanent strain after the
Paute et al.
(1988)
1p
first 100 cycles
A,D parameter function of
stress level
A N
N D
1p permanent axial strain after
q
p p*
f N
q
b m
*
p p
the first 100 cycles
b, p* model parameters
m slope of failure line in p-q
space
f(N) function of the number of
cycles N
Paute et al.
(1994)
Huurman
(1997)
p N A
A, B, C, D, parameter function
of the level of stress
PD Q e dN A e bN Q A
PD m N a1 e bN
First two equations for stable
state, and last for unstable
state.
PD (mm): vertical permanent
deformation
A, Q, a, b, c, d, m: stress
dependent parameters
Theyse
(2000)
p
1
B
D N
N
C e 1000 1
1000
PD m N
cN
b
cN
1
a
1/ b
Lmax
Gidel et al.
(2001)
Hornych
and El Abd
(2004)
N B L
N 1 max
N 0 Pa
p
1
Lmax
Pa
2
pa = 100 kPa, N0 reference
number of cycles,
1
m s qmax
pmax pmax
of the model.
1
m s qmax
pmax
pmax
f(N) - adopt Sweere (1990)
model or Hornych et al. (1993)
model
p
10
1p N f N
n
2
pmax qmax
n
109
10p , B, n, m, s are parameters
From Table 2-23, Khedr (1985), Sweere (1990) and Vuong (1994) models are
all a form of the power model. Since the power model is known to fit PD test
data very well and since it is simple, it has formed the basis of f(N) in some of
the models in Table 2-25.
Naturally, the third class of models is superior because it captures two of the
most important factors that affect PD. Of the models in this class, there are
two that model the stable (Range A) and unstable (Ranges B and C) PD
behavior: (a) Theyse (2000) and (b) Huurman (1997) models. Theyse used
separate equations to model the stable and unstable behaviors whereas
Huurman proposed an all encompassing equation that is more elegant. In
Table 2-25, Huurman used the power model in the first term of the equation
below:
B
D N
N
p N A
C e 1000 1
1000
(2.10)
where:
p(%) = permanent strain at load cycle N
N = number of cycles
e = base of natural logarithm (2.17828......)
σ
A a1 1
σ1f
a2
σ
B b1 1
σ1f
b2
σ
C c1 1
σ1f
c2
σ
D d1 1
σ1f
d2
a1, a2, b1, b2, c1, c2, d1, d2 are regression constants
110
1 = major principal stress
σ1f
1 sinφ σ3f 2 c cosφ
1 sinφ
major principal stress at failure
3f = minor principal stress at failure
= angle of internal friction
c = cohesion
The first term describes a linear increase of permanent strain with number of
load cycles on a log-log scale. The parameter A gives the permanent strain at
1000 cycles, and B gives the subsequent slope of the permanent strain with
number of load cycles.
The unstable behaviour at high stress level cannot be described by the first
term alone because the PD increases exponentially rather than linearly with
load cycles. Hence, Huurman introduced the second term.
In this model, parameters A, B, C and D are stress dependent. The other
models in Table 2-25 were not considered because (1) they require lateral
strain, which was not measured (e.g. Pappin (1979) model) (2) there is
insufficient details provided to fully define the model (e.g., 10p in Gidel‘s
(2001) model, and in many other models, it is not defined under what
conditions are the failure deviator stresses measured); (3) they were
published in a foreign language (e.g. Paute, 1994 model).
111
2.11.2 SELECTION OF CONFINING STRESS
To run the single- and multi-stage PD tests, a representative confining stress
is needed.
Its value depends on the: (1) pavement layer thickness; (2)
material properties; (3) design traffic load; and (4) stress history of the
unbound base course.
The confining stress for the PD tests was derived by assuming a pavement
section consisting of 6 inches of asphalt concrete, overlying 8 inches of base
course (friction angle = 45°) overlying subgrade. The confining stress at the
middle of base course was determined by assuming that the base course is
proof-rolled with a drum roller. From Clough and Duncan (1991), the locked-in
lateral stress at a depth of 4 inches can easily reach 3 psi based on a friction
angle of 45°. Thus, a horizontal stress of 3.0 psi or 21 kPa was adopted for all
PD tests.
2.11.3 SELECTION OF DEVIATOR STRESSES FOR PD TESTING
In the absence of a standard for single-stage PD test in the United States, the
strategy adopted was to select an arbitrary deviator stress corresponding to a
fraction of the failure deviator stress. The deviator stress is then adjusted
until both shakedown and incremental collapse is observed with the criterion
that at least three deviator stresses be applied per material.
PD tests were performed on the following: (1) VA; (2) RCA; (3) 50%
RCA:50% VA blend (RCA&VA); (4) RAP; and (5) 50% RAP:50% VA blend
(RAP&VA). For all samples, the target physical states are optimum water
112
content and maximum dry density based on the modified Proctor test
(AASHTO T180).
The test equipment and sample preparation method are identical to those for
the resilient modulus tests as described in Section 2.10.
As discussed
previously, the external sample LVDTs provide the sample deformation while
the system LVDT attached to the actuator provides the system deformation.
The maximum range of the sample LVDTs is 10 mm corresponding to 5%
vertical strain, which is inadequate for PD testing that involves larger strains.
Therefore, in the PD tests, all deformations were measured using the system
LVDT.
The PD test matrix is summarized in Table 2-26, along with the failure
deviator stresses measured with the drainage valve open during test. Multistage PD test is even more obscure than the single-stage variety with
specifications available only in Europe. The loading sequence for a multistage PD test on a blend of RCA&VA is given in Table 2-27 as an example.
All samples were conditioned by applying 500 cycles of a 95 kPa deviator
stress at a confining stress of 105 kPa. This is similar to the conditioning
specified in AASHTO T307 for resilient modulus testing of unbound
base/subbase.
The maximum number of cycles in the single-stage PD tests and multi-stage
PD tests are about 60,000 and 14,000, respectively. The single and multistage PD tests were terminated earlier if the samples failed.
113
Table 2-26 Single-stage PD test matrix and shear test results
Deviator
Stress
Failure
Applied
Deviator
Normalized
Deviator
Deviator
Materials
Stress Level
with Confining
stress1
stress
Stress
df
d
d/df
d/3
(kPa)
(kPa)
(%)
210
30%
10.0
330
47%
15.7
VA
700
420
60%
20.0
550
79%
26.2
660
94%
31.4
240
30%
11.4
RCA
800
400
50%
19.0
560
70%
26.7
174
30%
8.3
RCA&VA
580
290
50%
13.8
406
70%
19.3
204
60%
9.7
238
70%
11.3
RAP
340
272
80%
13.0
340
100%
16.2
102
30%
4.9
170
50%
8.1
RAP&VA
340
238
70%
11.3
Note 1 Triaxial testing was performed on the compacted specimen under a confining
stress of 21 kPa. A shear rate of 1%/minute was adopted.
114
Table 2-27 Multi-stage PD test load sequence for RCA&VA
Number of
Cycles
Applied
Confining
Stress
Applied
Seating
Stress
Applied
Deviator
Stress 1
Deviator
Stress
Level3
N
3
-
d
d/df
5002
0-1000
1000-2000
2000-3000
3000-4000
4000-5000
5000-6000
6000-7000
7000-8000
8000-9000
9000-10000
10000-11000
11000-12000
12000-13000
13000-14000
14000-15000
15000-16000
16000-17000
17000-18000
18000-19000
19000-20000
(kPa)
105
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
21
(kPa)
10
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
(kPa)
95
29
58
87
116
145
174
203
232
261
290
319
348
377
406
435
464
493
522
551
580
(%)
16%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
Notes
1 This load sequence is not the same for all materials.
2 500 cycles were applied to condition all samples, consistent with AASHTO T 307 for
resilient modulus testing of unbound base/subbase. These cycles are not included in the
cycle count in column 1.
3 Ratio of applied deviator stress to the failure deviator stress.
115
2.11.4 PD TEST RESULTS
2.11.4.1 Target Sample Water Content and Dry Density
The target and actual molding water contents and dry densities are listed in
Table 2-28 for each applied deviator stress level. The water contents of the
samples after testing were consistently smaller than those before testing as
drainage was permitted during the test. All samples have water contents and
dry densities within 1.4% of the target values.
116
Table 2-28 Water content and dry density for single-stage PD tests
Materials
VA
RCA
RCA&VA
RAP
RAP&VA
Deviator Target
Stress
Water
Level
Content
Water Content before Test
d/d,f
desired
before
Mean
COV
(%)
30%
47%
60%
79%
94%
30%
50%
70%
30%
50%
70%
60%
70%
80%
100%
30%
50%
70%
(%)
10.8%
10.8%
10.8%
10.8%
10.8%
11.0%
11.0%
11.0%
11.0%
11.0%
11.0%
5.6%
5.6%
5.6%
5.6%
9.0%
9.0%
9.0%
(%)
11.5%
11.3%
11.1%
10.6%
10.1%
10.8%
11.4%
12.0%
12.4%
11.8%
12.3%
5.6%
5.6%
5.6%
5.7%
9.4%
9.9%
9.7%
(%)
-
10.9%
5.2%
11.4%
5.3%
12.2%
2.6%
5.6%
0.9%
9.7%
2.6%
Deviation
from
Mean
(%)
5.3%
3.5%
1.6%
-2.9%
-7.5%
-5.3%
0.0%
5.3%
1.9%
-3.0%
1.1%
-0.4%
-0.4%
-0.4%
1.3%
-2.8%
2.4%
0.3%
117
Water
Target
Content
Dry
after
Density
Test
Dry Density before Test
after
d
d
Mean
COV
(%)
10.7%
9.5%
9.5%
9.7%
9.5%
9.9%
10.6%
10.2%
11.0%
11.0%
11.1%
4.6%
4.5%
4.2%
4.5%
9.0%
7.5%
7.7%
kgm-3
1833
1833
1833
1833
1833
1884
1884
1884
1867
1867
1867
2003
2003
2003
2003
1916
1916
1916
kgm-3
1821
1825
1828
1836
1845
1887
1877
1867
1844
1854
1845
2003
2003
2003
2001
1909
1900
1904
kgm-3
-
1831
0.5%
1877
0.5%
1848
0.3%
2003
0.0%
1904
0.2%
Deviation
from
Mean
(%)
-0.5%
-0.3%
-0.2%
0.3%
0.7%
0.5%
0.0%
-0.5%
-0.2%
0.3%
-0.1%
0.0%
0.0%
0.0%
-0.1%
0.2%
-0.2%
0.0%
2.11.4.2 Behavioral Ranges from Single-Stage PD Tests
Plots of permanent strain and resilient modulus versus number of cycles, and
permanent strain rate versus permanent strain are presented in Figure 2-44
through Figure 2-48 for all materials subjected to single-stage PD testing.
20
30% σdf
47% σdf
60% σdf
79% σdf
94% σdf
Permanent Strain (%)
15
10
5
0
0
10000
20000
30000
40000
No. of Cycles
Figure 2-44a Permanent strain versus N at different deviator stress levels for
VA
118
Resilient Modulus (MPa)
200
30% σdf
47% σdf
60% σdf
79% σdf
94% σdf
150
100
50
0
10000
20000
30000
40000
No. of Cycles
Figure 2-44b Resilient moduli versus N at different deviator stress levels for
VA
Permanent strain (%)
-3
Permanent strain rate(x10 %/cycle)
0
5
10
15
20
1.E+01
1.E+00
1.E-01
30% σdf
47% σdf
60% σdf
1.E-02
79% σdf
94% σdf
1.E-03
Figure 2-44c Permanent strain rate versus permanent strain at different
deviator stress levels for VA
119
Permanent Strain (%)
10
30% σdf
8
50% σdf
70% σdf
6
4
2
0
0
10000
20000
30000
40000
No. of Cycles
Figure 2-45a Permanent strain versus N at different deviator stress levels for
RCA
400
Resilient Modulus (MPa)
30% σdf
50% σdf
300
70% σdf
200
100
0
0
10000
20000
30000
40000
No. of Cycles
Figure 2-45b Resilient moduli versus N at different deviator stress levels for
RCA
120
Permanent Strain (% )
-3
Permanent Strain Rate (10 %/cycle)
0
2
4
6
8
10
1.E+01
1.E+00
30% σdf
50% σdf
1.E-01
70% σdf
1.E-02
1.E-03
Figure 2-45c Permanent strain rate versus permanent strain at different
deviator stress levels for RCA
Permanent Strain (%)
10
8
30% σdf
50% σdf
6
70% σdf
4
2
0
0
10000
20000
30000
40000
No. of Cycles
Figure 2-46a Permanent strain versus N at different deviator stress levels for
RCA&VA
121
Resilient Modulus (MPa)
200
150
30% σdf
100
50% σdf
70% σdf
50
0
10000
20000
30000
40000
No. of Cycles
Figure 2-46b Resilient moduli versus N at different deviator stress levels for
RCA&VA
Permanent strain (%)
-3
Permanent strain rate (10 %/cycle)
0
2
4
6
8
10
1.E+01
1.E+00
30% σdf
1.E-01
50% σdf
70% σdf
1.E-02
1.E-03
Figure 2-46c Permanent strain rate versus permanent strain at different
deviator stress levels for RCA&VA
122
10
60% σdf
Permanent Strain (%)
8
70% σdf
80% σdf
6
100% σdf
4
2
0
0
20000
40000
60000
No. of Cycles
Figure 2-47a Permanent strain versus N at different deviator stress levels for
RAP
Resilient Modulus (MPa)
250
200
60% σdf
70% σdf
80% σdf
100% σdf
150
100
50
0
10000
20000
30000
40000
50000
60000
No. of Cycles
Figure 2-47b Resilient moduli versus N at different deviator stress levels for
RAP
123
Permanent Strain (% )
0
2
4
6
8
10
-3
Permanent Strain Rate(x10 %/cycle)
1.E+01
1.E+00
1.E-01
60% σdf
70% σdf
1.E-02
80% σdf
100% σdf
1.E-03
Figure 2-47c Permanent strain rate versus permanent strain at different
deviator stress levels for RAP
10
Permanent Strain (%)
30% σdf
8
50% σdf
70% σdf
6
4
2
0
0
10000
20000
30000
40000
No. of Cycles
Figure 2-48a Permanent strain versus N at different deviator stress levels for
RAP&VA
124
Resilient Modulus (MPa)
150
100
30% σdf
50% σdf
70% σdf
50
0
10000
20000
30000
40000
No. of Cycles
Figure 2-48b Resilient moduli versus N at different deviator stress levels for
RAP&VA
Permanent strain (% )
0
2
4
6
8
10
-3
Permanent Strain Rate(x10 %/cycle)
1.E+01
1.E+00
30% σdf
1.E-01
50% σdf
70% σdf
1.E-02
1.E-03
Figure 2-48c Permanent strain rate versus permanent strain at different
deviator stress levels for RAP&VA
125
The behavioral ranges for all materials tested are also summarized in Table
2-29.
Table 2-29 Behavioral ranges based on a single-stage PD testing
Number of
Range of
Deviator
Load Cycles Behavioral
Plastic
Material
Stress Level
Ranges 1
at End of
Shakedown
Test
Limit
VA
RCA
RCA&VA
RAP
RAP&VA
d/df
N
-
-
(%)
30%
47%
60%
79%
94%
30%
50%
70%
30%
50%
70%
60%
70%
80%
100%
30%
50%
70%
39600
39600
38400
8200
6800
39400
39400
1200
34400
19800
4400
54200
59200
39600
6000
39200
39200
19800
A
B
C
C
C
A
B
C
A
A
C
A
A
B
C
A
A
B
(kPa)
210-330
240-400
290-406
238-272
170-238
Note
1 A: plastic shakedown; B: plastic creep; C: incremental collapse. Behavioral range
classification based on plots of permanent strain rate versus permanent strain.
Plastic shakedown
Plastic shakedown was observed in all the materials. From Figures 2-44a
through 2-48a, the maximum permanent strains were generally less than 2%,
and do not increase much with number of cycles.
126
From Figures 2-44b through 2-48b, it can be observed that the resilient
modulus increases slightly or remains constant during shakedown.
From Figures 2-44c through 2-48c, the permanent strain rates decreased
linearly with permanent strain during shakedown.
Incremental Collapse
Incremental collapse was observed in VA, RCA, RCA&VA and RAP but not in
the RAP&VA samples.
From Figures 2-44a through 2-48a, the permanent strain increases
asymptotically with increasing number of cycles with failure occurring at a
relatively small number of load cycles.
During incremental collapse, the resilient modulus decreased or the resilient
strain increased with increasing number of load cycles. This is contradictory
to the trend of decreasing resilient strain with increasing number of load
cycles published by Werkmeister et al. (2003). Two notable differences exist
between their tests and the ones performed herein.
Their samples were
subjected to a loading frequency of 5Hz instead of 1Hz and their confining
stresses are about 3 times higher than the value used in our test program
(21kPa). At high load frequencies, there is a question as to whether the
material will: (1) behave in a drained fashion; a more undrained behavior
generally implies a stiffer response; and (2) have time to rebound due to
viscous effects.
127
From Figures 2-44c through 2-48c, it can be observed that the permanent
strain rate initially decreased. Then, it tended to a constant or increased
slightly when the sample failed.
Plastic Creep
This intermediate behavior can be observed only with the permanent strain
rate versus permanent strain plots of Figure 2-44c through 2-48c.
This
behavior is not observed in the other plots, because a large number of load
cycles are required for failure to occur.
Thus, the permanent strain rate
versus permanent strain plot is least ambiguous for characterizing the various
behavioral ranges.
2.11.4.3 Models for Single-Stage PD Tests
Historically, the power law model by Sweere (1990 - see Table 2-23) has
been used widely to model PD test results because it is known to capture
shakedown behavior well (Dawson 2008). The model is as follows:
p=ANB
(2.11)
where p(%) = permanent strain, N = number of cycles and A and B are
regression parameters.
When Equation 2.11 is used to fit the PD test data, the power law model
provided excellent fits to the data overall.
The model parameters for the
materials tested are summarized in Table 2-30.
coefficients of determination, R2, are all above 0.91.
128
It can be seen that the
Equation 2.11 relates permanent strain to number of cycles only.
When
parameters A and B are plotted against deviator stress level (σd/σdf) for VA,
as shown in Figures 2-49a and b, respectively, it can be seen that both A and
B vary with deviator stress levels. In light of this observation, it would be
advantageous to develop permanent strain models that vary with both
number of cycles and stress level.
Table 2-30 Power law model parameters for all materials tested
Applied
Deviator
Parameter Parameter
Materials
R2
Deviator
Stress
A
B
Stress
Level
VA
RCA
RCA&VA
RAP
RAP&VA
d
d/df
-
-
-
(kPa)
210
330
420
550
660
240
400
560
174
290
406
204
238
272
340
102
170
238
(%)
30%
47%
60%
79%
94%
30%
50%
70%
30%
50%
70%
60%
70%
80%
100%
30%
50%
70%
0.095
0.002
1.0E-04
2.0E-06
7.0E-05
0.258
0.062
0.003
0.230
0.354
0.003
0.239
0.493
0.181
0.226
0.177
0.109
0.105
0.225
0.692
1.089
1.781
1.350
0.051
0.409
1.009
0.089
0.167
0.926
0.090
0.148
0.323
0.408
0.116
0.129
0.408
0.999
0.941
0.971
0.945
0.914
0.941
0.999
0.961
0.970
0.974
0.946
0.985
0.982
0.985
0.999
0.995
0.998
1.000
129
1.0E-01
Test data
Power (Test data)
1.0E-02
A
1.0E-03
1.0E-04
y = 4.00E-06x-8.01
R2 = 0.80
1.0E-05
1.0E-06
20%
40%
60%
80%
100%
Deviator Stress Level (% )
Figure 2-49a Power law model parameters A versus deviator stress level for
VA
2.5
Test data
2.0
Power (Test data)
B
1.5
1.0
y = 2.15x1.71
R2 = 0.89
0.5
0.0
20%
40%
60%
80%
100%
Deviator Stress Level (% )
Figure 2-49b Power law model parameters B versus deviator stress level for
VA
130
In addition to the Huurman (1997) model, another model that relates
permanent strain to both number of cycles and stress levels is the Tseng and
Lytton (1989) model. These two models were evaluated because: (1) they
involve only one equation; and (2) they are both mathematically capable of
modeling behavioral ranges varying from shakedown to incremental collapse.
Also, the Tseng and Lytton (1989) model has been adopted in the MEPDG.
The Huurman model is presented first.
The regression constants for this
model (Equation 2.10) for all the materials tested are summarized in Table 231. This table shows that except for VA, the parameters c1 and d1 are all zero
indicating that the second term in the Huurman (1997) model is zero. For VA,
although the parameters c1 and d1 are not zero, their t-statistics are smaller
than 2.0 (Table 2-32), indicating that the second term in the Huurman model
is statistically insignificant and should be discarded.
Table 2-31 Summary of regression constants for the Huurman model
N
B
D 1000
N
p A
1
C e
1000
Material
a1
a2
b1
b2
c1
c2
d1
d2
VA
RCA
RCA&VA
RAP
RAP&VA
0.008
0.046
0.031
0.035
0.039
1.623 1.850 1.320
2.179 9.630 4.756
1.606 6.290 5.401
4.311 0.534 1.843
2.949 21.500 11.461
131
1.8E-05
0.0E+0
0.0E+0
0.0E+0
0.0E+0
1.986
4.097
4.098
7.008
5.230
0.688
0.0E+0
0.0E+0
0.0E+0
0.0E+0
2.314
4.532
4.532
4.452
3.610
Table 2-32 Parameter estimates and t-statistics for VA using the Huurman
model
95% Confidence Interval
Std.
tParameter
Estimate
Error
statistics Lower Bound Upper Bound
a1
a2
b1
b2
c1
c2
d1
d2
0.008
1.623
1.850
1.320
1.800E-05
1.986
0.688
2.314
0.002
0.476
0.135
0.156
0.003
373.466
24.163
71.608
4.120
3.412
13.685
8.468
0.005
0.005
0.028
0.032
0.004
0.689
1.584
1.014
-0.006
-731.329
-46.757
-138.291
0.012
2.557
2.115
1.626
0.006
735.301
48.133
142.920
Without the second term, the first term of the Huurman model reverts to the
power model. The data was re-analyzed using the power model and the
regression constants for all materials are summarized in Table 2-33. The
parameter estimates and t-statistics for VA as an example are summarized in
Table 2-34. The t-statistics for all materials are all larger than 2.0, indicating
statistical significance.
Table 2-33 Summary of regression constants for the first term of the Huurman
model
N
p A
1000
B
Material
a1
a2
b1
b2
VA
0.007
1.846
1.9708
1.218
RCA
0.046
2.179
9.630
4.756
RCA&VA
0.031
1.606
6.290
5.401
RAP
0.035
4.311
0.534
1.843
RAP&VA
0.039
2.949
21.500
11.461
132
Table 2-34 Parameter estimates and t-statistics for the first term of the
Huurman model for VA
95% Confidence Interval
tParameter Estimate Std. Error
Lower
Upper
statistics
Bound
Bound
a1
0.007
0.001
4.888
0.004
0.009
a2
1.846
0.411
4.493
1.039
2.653
b1
1.971
0.132
14.949
1.712
2.230
b2
1.218
0.134
9.060
0.954
1.482
A comparison of the predicted and measured permanent strain as a function
of number of cycles and deviator stress levels for VA is shown in Figure 250a.
Figure 2-50b shows a comparison of the predicted and measured
permanent strain with respect to a 1:1 line. It is observed that the first term of
the Huurman model or the power model, is able to capture the data at low
deviator stresses well.
At high deviator stress levels where the material
incrementally collapses, the fit is not as good. This makes sense since the
power model captures only shakedown behavior well.
The Huurman model utilizes 1f as one of its parameters. However, σ1f is
sensitive to the molding water content and suction, etc. and can be highly
variable especially when partially saturated.
To avoid reliance on a
parameter that can be so widely divergent, an alternative form of the stress
ratio term
1
3
instead of
1
1f
was
also investigated, where 3 is the
confining stress. This model is termed the modified Huurman model.
133
Figure 2-50a Predicted versus measured PD using first term of the Huurman
model
Figure 2-50b Predicted versus measured PD using first term of the Huurman
model
134
When regression analysis was performed to derive the eight regression
constants for the materials tested, again only the first term of the modified
Huurman model was statistically significant. These four regression constants
are summarized in Table 2-35. The parameter estimates and t-statistics for
VA as an example are summarized in Table 2-36. (Note a1 is a necessary
parameter and cannot be discarded even though the t-statistic is 0.787.) The
majority of the t-statistics for all material types are larger than 2.0, indicating
statistical significance.
Table 2-35 Summary of regression constants for the first term of the modified
Huurman model
N
1000
B
p A
Material
a1
a2
b1
b2
VA
9.56E-06
1.85
0.03
1.22
RCA
1.47E-05
2.20
3.99E-07
4.61
RCA&VA
1.47E-04
1.60
8.18E-08
5.42
RAP
1.65E-07
4.31
2.83E-03
1.84
RAP&VA
2.33E-07
4.45
7.61E-08
6.19
Table 2-36 Parameter estimates and t-statistics for the first term of the
modified Huurman model for VA
Parameter
Estimate
Std. Error
tstatistics
a1
9.559E-06
1.215E-05
a2
1.846
b1
b2
95% Confidence Interval
Lower
Bound
Upper
Bound
0.787
-1.430E-05
3.342E-05
0.411
4.493
1.039
2.653
0.027
0.011
2.416
0.005
0.048
1.218
0.134
9.060
0.954
1.482
A comparison of the predicted and measured permanent strain for VA is
shown in Figure 2-51.
135
20%
Predicted - solid line
Permanent Strain (%)
Measured 30% σdf
Measured 47% σdf
15%
Measured 60% σdf
Measured 79% σdf
Measured 94% σdf
10%
5%
0%
0
10000
20000
30000
Number of Cycles
40000
Figure 2-51a Predicted versus measured PD using the first term of the
modified Huurman model
Predicted Permanent Strain (%)
20%
Line of Equality
30% σdf
47% σdf
15%
60% σdf
79% σdf
y = 0.918x
94% σdf
R = 0.863
2
10%
5%
0%
0%
5%
10%
15%
Measured Permanent Strain (% )
20%
Figure 2-51b Predicted versus measured PD using the first term of the
modified Huurman model
136
The Tseng and Lytton (1989) model was also evaluated by correlating its
three parameters (A, B and C) with stress level in a power law format. This
way, the model can predict PD as a function of N and stress level. The
modified Tseng and Lytton (1989) model is as follows:
B
N
C
a1 1
3
a
p Ae
where A =
(2.12)
2
1
b
, B = 1 3
b2
1
c
, C = 1 3
c2
, e = base of natural
logarithm (2.17828…) and a1, a2, b1, b2, c1, and c2 are regression constants.
During non-linear regression, the exponential term became either very large
or very small leading to convergence issues. As a result, further investigation
on the use of this model was abandoned.
Regression results for all the materials tested using the first term of the
Huurman and modified Huurman models are summarized in Table 2-37.
Table 2-37 Summary of the bias (slope) and coefficient of determination for
the models evaluated
First Term of the
First Term of the
Material
Modified Huurman
Huurman Model
Model
VA
RCA
RCA&VA
RAP
RAP&VA
Slope
0.918
1.000
0.992
0.988
0.978
R2
0.863
1.000
0.983
0.966
0.966
137
Slope
0.918
1.000
0.992
0.988
0.975
R2
0.863
1.000
0.983
0.966
0.961
The slope represents the bias of the prediction model and the R2 represents
the degree of scatter (or variability) of the data in relation to the model. Three
indicators can be used to evaluate the models: (1) bias; (2) variability; and (3)
simplicity. In terms of bias and variability, the first term of the Huurman model
is just a little better off than the first term of the modified Huurman model. In
terms of simplicity, the modified Huurman model requires less laboratory work
since it does not require determination of the failure principle stress.
2.11.4.4 Multi-Stage PD Tests
Multiple single-stage PD tests must be conducted to determine the
shakedown limit. Disadvantages of single stage PD tests include: (1) There
may be variability among the individual samples which can adversely
influence the interpretation of the shakedown limit; and (2) Performing
multiple tests requires a significant amount of time.
In light of these
shortcomings, it may be worth considering multi-stage PD tests.
Multi-stage PD tests were also performed to verify whether they provide
shakedown limits that are consistent with the single-stage PD tests on
multiple samples. Standards are available in Europe to perform single- and
multi-stage PD tests but not in the United States. In the European standard
(CEN EN 13286-7), both the confining and deviator stresses vary in multistage PD testing. A loading frequency between 0.2 and 10 Hz is permitted.
In the US, multi-stage PD testing was recently performed by Saeed (2008) as
part of NCHRP Project 598. Saeed recommended a multi-stage PD test load
sequence in which the confining stress is a constant (103.4 kPa) and the load
138
frequency is 1 Hz (0.1s load pulse with a 0.9s rest period). The number of
load cycles in NCHRP Report 598 was used in this study. Details of the load
sequence for the multi-stage PD tests are as follows:
1. The confining stress was kept constant throughout the test (21 kPa)
and selected to be consistent with the value used in resilient modulus
and single-stage PD tests. This allows a proper comparison of the
shakedown limit from both single- and multi-stage tests to be made.
2. The deviator stress encompassed those used in the single–stage tests
and were varied over a wide range to capture plastic shakedown
through incremental collapse. A thousand load cycles of each deviator
stress were applied as recommended in NCHRP Report 598.
2.11.4.5 Multi-Stage PD Test Results and Analysis
Results of multi-stage PD tests are presented in Table 2-38 in terms of the
stress ratio at permanent strains of 1%, 2%, 5% and 10%.
From these
results, the VA and RCA are superior in terms of resistance to PD since they
are able to sustain the highest stress ratios at a given permanent strain. It is
quite surprising that the 50% RCA:50% VA did not fare as well as the
unblended ingredients. However, clearly, the RAP and its blend are most
susceptible to PD.
This may be attributable to the fact that the asphalt
caused the particles to deform within themselves more readily. It should be
noted that the deviator stress increments applied are not consistent for each
material type. This is because the increments were chosen to be between 5
to 15% of the failure deviator stresses, which are quite variable (Table 2-26).
139
Table 2-38 Summary of stress ratios at different permanent strains in multistage permanent deformation tests.
Stress Ratio (1/3) at the following Permanent Strains
Material
1%
2%
5%
10%
VA
32.4
32.4
RCA
31.4
35.2
50% RCA:50% VA
16.2
18.9
RAP
15.6
17.2
50% RAP:50% VA
9.1
10.7
Notes:
1) 1 = major principal stress = deviator stress + 3.
2) 3 = minor principal stress.
37.6
35.2
20.3
20.4
12.3
37.6
35.2
21.7
22.0
12.3
A big uncertainty in multi-stage PD tests is the determination of the
shakedown limit. A method is proposed below, followed by a comparison of
its predictive capability with those from single-stage PD test results.
When the results are plotted in terms of resilient modulus (at 200 cycle
intervals) versus number of cycles (Figure 2-52 shows the results for RCA),
an interesting observation is made. At a low constant deviator stress (≤ 400
kPa), the resilient moduli increased with increasing number of cycles
indicative of modulus hardening during shakedown. At high constant deviator
stresses (> 400 kPa), the resilient moduli decreased with increasing number
of cycles (modulus softening) indicative of Range B and C behavior.
Alternatively, the plot could be made in terms of resilient strain versus number
of cycles except that the slope changes would be in reverse.
140
Only the curve for RCA is shown in Figure 2-52 for brevity. Curves for all
other materials tested have similar trends. Based on this sudden switch in
the resilient modulus trend, it is rational to assume that:
1) a deviator stress of 400 kPa is a lower bound for the shakedown limit
of RCA under a confining pressure of 21 kPa; and
2) a deviator stress > 400 kPa is indicative of either plastic creep (Range
B) or incremental collapse (Range C) of the RCA under a confining
pressure of 21 kPa.
The behavioral range limits for all other materials tested are summarized in
Table 2-39. Based on these limits, the behavioral range of the single-stage
samples are evaluated and also summarized in the same table. It can be
seen that 14 predictions out of 18 are correct (78% reliability).
Possible
reasons why the agreement is not perfect include: (1) variability among the
single- and multi-stage samples; and (2) the number of cycles per deviator
stress and number of deviator stresses are limited in a multi-stage test.
However, considering these differences, the success rate is noteworthy and
multi-stage PD testing can provide an economical alternative to characterize
the PD behavior of geomaterials.
Additional testing is needed to further
validate this procedure. To facilitate this, a standard test load sequence is
needed. The one proposed by Saeed (2008) presents a good starting point
with perhaps a suggestion that the confining stress should be representative
of the field pavement section to be studied.
141
Permanent Strain (%)
3
2
1
0
0
2000 4000 6000 8000 10000
No. of Cycles
(a)
-6
Resilient Strain (x10 )
Mr slope increasing
r slope decreasing
Resilient Strain
Resilient Modulus
480 kPa
560 kPa
400 kPa
4000
250
200
320 kPa
640 kPa
240 kPa
720 kPa
2000
150
160 kPa
Mr slope decreasing
r slope increasing
80 kPa
0
Resilient Modulus (MPa)
6000
100
0
2000 4000 6000 8000 10000
No. of Cycles
(b)
Figure 2-52 Multi-stage permanent deformation test results for recycled
concrete aggregate (RCA): (a) Permanent strain versus number of cycles and
(b) Resilient modulus/strain versus number of cycles. Deviator stresses are
notated in figure.
142
Table 2-39 Behavioral ranges based on a single- and multi-stage PD testing.
Single-Stage Tests
Multi-Stage Tests
Predicted
Lower
Deviator
Range of
Single-stage
Behavioral
Bound
Stress in
Plastic
Sample
Ranges
Shakedown
Single- Shakedown
Behavioral
Material
Limit based
based on
Accuracy
stage
Limit based
Range
on MultiSingle-stage
Tests
on SingleUsing MultiTests1
stage Tests
σd
stage Tests
Stage Test
(Range A)
Results
(kPa)
(kPa)
(kPa)
210
A
A
√
330
B
B/C
√
VA
420
210-330
C
217
B/C
√
550
C
B/C
√
660
C
B/C
√
240
A
A
√
400
B
A
x
RCA
240-400
400
560
C
B/C
√
174
A
A
√
50% RCA:50% VA
290
290-406
A
174
B/C
x
406
C
B/C
√
204
A
A
√
238
A
B/C
x
RAP
238-272
204
272
B
B/C
√
340
C
B/C
√
102
A
A
√
170
A
B/C
x
50% RAP:50% VA
170-238
102
238
B
B/C
√
Note: 1) Behavioral range classification based on plots of permanent strain rate versus permanent strain. A= plastic shakedown;
B = plastic creep; C = incremental collapse.
143
2.11.5 SUMMARY AND CONCLUSIONS
A confining stress of 21 kPa was used for all single- and multi-stage PD tests
conducted on VA, RCA, RCA&VA, RAP and RAP&VA. The following summary
and conclusions are offered:
No agreed upon set of specifications for measuring PD have been
established in the United States.
The MEPDG combines the results of a mechanistic analysis of the various
pavement layers with empirical pavement distress relationships to
compute the incremental damage over time. The plastic deformation of
each layer is summed and compared to the allowable value based on the
rutting criteria.
Upon application of a moving wheel load, a pavement element is
subjected to a rotation of principal stresses. This rotation is not captured
by regular CCP RLT test, but may be captured by more advanced VCP
RLT tests.
Pavement stresses consist of overburden pressure, compaction-induced
locked-in stresses and traffic induced stresses. The compaction-induced
locked-in stresses are difficult to determine and seldom addressed in
pavement design.
A direct dependency between the shear strength and PD resistance does
not exist. PD is a function of the number of load cycles, confining and
144
deviator stresses, water content, density, stress history, stress paths,
gradation and particle angularity and roughness.
Three possible behavioral ranges are possible in a PD test. They include
(a) plastic shakedown (Range A); (b) plastic creep (Range B); and (c)
incremental collapse (Range C). The limit between plastic shakedown
and plastic creep is known as the plastic shakedown limit.
The limit
between plastic creep and incremental collapse is known as the plastic
creep limit.
When interpreting single-stage PD test results, it is least ambiguous to use
the vertical permanent strain rate versus permanent strain plot to
distinguish between the behavioral ranges.
This is because Range B
behavior cannot be easily observed when plotting results in terms of
number of cycles since a very large number of cycles are sometimes
required to eventually collapse the sample.
In single stage PD testing, modulus hardening was observed during
plastic shakedown and modulus softening during plastic creep and
incremental collapse. The latter is contradictory to trends observed by
Werkmeister et al. (2004). The difference can be explained as follows:
their samples were subjected to a much higher loading frequency (5Hz
instead of 1Hz). At high load frequencies, the material tends to behave in
a more undrained fashion leading to a stiffer resilient response.
Also,
there is inadequate time for the sample to recover from viscous effects.
145
Ideally, UGM should be designed to limit the applied loads to less than the
shakedown load, wherein the growth of plastic strains level off or shakes
down as the UGM adapts to the applied loads.
At low deviator stress levels, the power law model predicts the permanent
strain in single-stage PD tests well.
The Huurman and modified Huurman models were evaluated using the
test data.
The second term of these two models was found to be
statistically insignificant. Neglecting the second term reverts them to the
power model. It should be noted that these models were developed for
the gradation tested and the applicability of these models to other
gradations should be verified
It was observed that the plastic shakedown limit and plastic creep limit at
constant confining stress can be determined by a series of single-stage
PD tests. However, there may be inherent variability among samples and
they require a considerable amount of time to test.
Alternatively, the
plastic shakedown limit may be discerned by conducting one multi-stage
PD test.
Based on the unique switch in the resilient modulus trend, multi-stage PD
tests can be used to interpret the shakedown limit for a material at a given
confining stress.
A procedure is proposed based on the fact that the
resilient modulus increases under low deviator stresses and decreases
when the deviator stresses are high or exceeds the shakedown limit.
146
When applied to the materials tested, the multi-stage test predicted
correctly the behavior of single-stage-test samples 78% of the time.
Possible reasons why the agreement is not perfect include variability
among the single- and multi-stage samples and the number of cycles per
deviator stress and number of deviator stresses are limited in a multistage test.
Additional research is needed to further validate this procedure.
facilitate this, a standard test load sequence is needed.
To
The one
proposed in NCHRP Report 598 presents a good starting point.
The
deviator stress intervals should be small enough to allow all three
behavioral ranges to be captured and the load frequency slow enough for
the sample to drain and recover.
One more suggestion is that the
confining stress be representative of the field pavement section to be
studied.
Based on multi-stage PD tests results presented in terms of stress ratios
at various permanent strain levels, the VA and RCA are superior in terms
of resistance to PD as compared to RAP. This may be attributable to the
fact that the asphalt caused the particles to deform within themselves
more readily.
This may be a potential concern and may require a
limitation on the amount of RAP allowed in the unbound layers.
147
CHAPTER 3 ASSESSING THE COMPACTABILITY OF RECYCLED
CONCRETE AGGREGATE AND RECLAIMED ASPHALT PAVEMENT
In this chapter, the characteristics of RCA and RAP during compaction in two 4foot-high, 3-foot-diameter, 3/16-inch-thick wall cross-linked polyethylene bins
(supplied by Chemtainer Industries, Inc. of Keaau, Hawaii) were studied. Their
compactability was assessed using (a) the nuclear gauge and Time Domain
Reflectometry (TDR) to measure the dry density and water content after
compaction; (b) the GeoGauge and Portable Falling Weight Deflectometer
(PFWD) to measure the stiffness of the soils after compaction; and (c)
FlexiForce® electrical sensors to estimate the compaction-induced lateral
pressures exerted by the RAP and RCA. It should be noted that in this chapter,
the RAP and RCA were tested neat; i.e., without blending.
3.1 BACKGROUND AND OBJECTIVES
3.1.1 Nuclear Gauge
The nuclear gauge (Figure 3-1) rapidly measures the in-place density and
moisture content of geomaterials by imparting low amounts of radiation. The
most effective mode of testing geomaterials is the direct transmission mode,
where the radiation source is inserted into a drilled hole. It can be lowered to a
maximum depth of 12 inches but in these experiments, a penetration depth of 6
inches was adopted as this corresponds to the lift thickness.
Two different types of radiation sources are used: (1) Cesium 137 that emits
gamma rays consisting of streams of photons. These photons collide with the
geomaterial causing some photons to lose energy, which inhibits detection by the
148
gauge. The density is determined using an inverse relationship with the amount
of photons that reach the detector. The density measured is the moist density;
and (2) Americium-beryllium isotope that emits neutrons to measure the moisture
content, which is determined by detecting the amount of hydrogen atoms present
in the geomaterial. The neutron detector only senses ―slow‖ neutrons. When the
neutrons collide with most soil particles, they are reflected with minimal energy
loss since these particles are much heavier than the neutrons.
When the
neutrons collide with elements having a similar mass such as the nuclei of
hydrogen atoms present in water, the neutrons slow down and are counted by a
detector, which translates this number to a moisture content.
Unlike the Cesium 137 isotope, the Americium-beryllium isotope is not lowered
into the ground but remains in the gauge. The nuclear gauge only measures
moisture content to a limited depth. 98% of the neutrons counted are above this
depth of measurement.
The depth of measurement is dependent on the
moisture content as follows (Troxler Electronic Laboratories, Inc., 2009):
Depth (inches) = 11 – 0.17W
(3.1)
where W (lbs) = weight of water in 1 cubic foot of geomaterial = w.d = - d, w =
water content, = moist unit weight and d = dry unit weight. The higher the
moisture content, the smaller is the depth of penetration. The nuclear gauge
then calculates the dry unit weight as follows.
(3.2)
d = - W
149
Figure 3-1 Troxler nuclear moisture/density gauge model 3450 used in the
experiments
3.1.2 Time Domain Reflectometry
Developed at Purdue University and distributed by Durham Geo Slope Indicator,
the time domain reflectometry (TDR) instrument used is the Moisture and Density
(M+D) Indicator MDI-2000 Series. The TDR system consists of a personal data
assistant (PDA), pulse generator, coaxial cable, probes to create an inner and
outer conductor, coaxial head and a template to guide the probes when driven
into the ground. Other components that came with the TDR include:
standard Proctor mold and collar
9-inch tall, 4-inch diameter cylindrical compaction mold
Center rod guide
150
Non-conductive base
The TDR method also provides the in-situ dry density and moisture content. By
passing an electromagnetic pulse through four multi-rod probes driven into the
geomaterial, the dielectric constant and bulk electrical conductivity of the
geomaterial are measured. These two parameters are used to calculate the
density and moisture content using relationships established by Siddiqui and
Drnevich (1995). Figure 3-2 shows the TDR set-up.
(a)
(b)
Figure 3-2 Time Domain Reflectometry test set-up (a) round coaxial head
connected to the TDR gauge which is operated using a PDA and (b) multi-rod
probes below the coaxial head
3.1.3 GeoGauge
Supplied by Humboldt Manufacturing Company, the GeoGauge (Figure 3-3) is
used to non-destructively and expediently measure the in place stiffness of a
geomaterial. An annular foot extends from the bottom center of the GeoGauge
and is the portion of the device that is in contact with the ground. The GeoGauge
151
applies a vibrating force at 25 steady state frequencies ranging from 100 to 196
Hz to produce small displacements on the geomaterial.
The GeoGauge
measures the force imparted to the surface and the resulting surface velocity,
which can be integrated to obtain displacement, as a function of time.
The
stiffness, force divided by deflection, is determined at each frequency and the
average is displayed. From the stiffness, the elastic modulus of the geomaterial
can be estimated.
Figure 3-3 GeoGauge device
3.1.4 Portable Falling Weight Deflectometer (PFWD)
Developed by Keros Technology and Carl Bro Pavement Consultants of
Denmark, the Portable Falling Weight Deflectometer (or PFWD – see Figure 3-4)
can be used to measure the in place stiffness of geomaterials.
A mass is
dropped from a particular height and causes the circular footing to deflect. A
geophone measures the acceleration, which can be integrated twice to obtain the
152
displacement. The impact force is measured using a load cell. The stiffness and
elastic modulus are estimated based on the force and displacement.
Figure 3-4 Portable falling weight deflectometer
3.1.5 FlexiForce® Electrical Sensors
Manufactured by Tekscan, Inc., FlexiForce® electrical sensors were used to
estimate the compaction-induced lateral pressures exerted by the RAP and RCA
against the bin walls. The active sensing area, consisting of a force sensing
resistor in an electrical circuit, is located at the end of the sensor (Figure 3-5).
Each sensor is connected to a transmitter, which sends the measured signal
wirelessly to a main hub that is connected to a computer.
153
Figure 3-5 FlexiForce® sensor
3.1.6 Objectives
The main objectives of this experiment are to:
1) Determine the applicability of the nuclear gauge and TDR to measure the
dry density and moisture content of RAP and RCA. The nuclear gauge
detects water by detecting hydrogen atoms present in water. However,
hydrogen is also present in asphalt, a component of RAP, and in cement
paste, a component of RCA. This research will shed light on the reliability
of the nuclear gauge when used with RCA and RAP. TDR has been used
for decades in the agricultural industry to measure the volumetric water
content of soils. More recently, a new version of this technology has been
devised to measure the dry density and gravimetric water content. This
instrument has not been used extensively on RAP and RCA and is
investigated herein.
2) Determine the applicability of the Portable Falling Weight Deflectometer
and GeoGauge in measuring the stiffness of RAP and RCA. There has
been a push by pavement engineers to assess the compactability of
geomaterials using stiffness instead of dry density and water content with
the advent of the MEPDG (ARA, Inc., 2004).
One of the key input
parameters in the design of pavements using the MEPDG is the resilient
154
modulus or stiffness. The capability of these two instruments to provide
the stiffness of RCA and RAP is assessed.
3) Estimate the compaction-induced lateral pressures of RAP and RCA.
Compaction typically results in lateral pressures that are significantly
above the normally consolidated at-rest values. These measurements will
show the magnitude of the compaction-induced lateral pressures.
Comparisons will then be made with values predicted from theory.
3.2 EXPERIMENTAL SET-UP
The experimental set-up is described in four sections. The first section discusses
the material characteristics. The second is on calibrating the instruments that
were used in the experiments. The third describes the bin set-up, installation of
force sensors, compaction equipment and process, and measurements made in
the polyethylene bins. The fourth focuses on post-compaction measurements as
a function of time.
3.2.1 Materials
As discussed in Chapter 2, the RAP and RCA were obtained from Grace Pacific
Corporation‘s quarry in Makakilo on the island of Oahu, Hawaii where RAP is
stockpiled by gradation; one pile for 3/4 inch minus RAP and another for 3/8 inch
minus RAP. The RCA was all crushed to one gradation.
To ensure that representative samples were taken from the stockpile, samples
were obtained from mid-height below the surficial aggregate since samples at the
bottom of the pile tend to be coarser.
155
3.2.1.1 Gradation
For the bin experiments, particles larger than ¾ inch were removed because their
presence could locally influence the results of the various tests.
Figure 3-6
shows the gradations for the RAP and RCA that were used in the experiments in
this chapter. The RAP consisted of a blend of the ¾- and 3/8-inch minus fraction
and contained little to no fines. It was not possible to create a 100% RAP blend
that meets the HDOT base-course gradation because the RAP was crushed to
two very uniform sizes.
After removing the ¾-inch plus material, the RCA
gradation met HDOT‘s 0.75-inch maximum nominal untreated base course
gradation requirements while RAP did not.
3.2.1.2 Classification
According to the USCS, the RAP and RCA in Figure 3-6 are classified as GP
(poorly-graded gravel) and GW (well-graded gravel), respectively. According to
the AASHTO classification, both the RAP and RCA are classified as A-1-a.
156
100%
#4 Sieve - 4.75 mm
# 200 Sieve -0.075 mm
90%
Percent Passing (%)
80%
70%
60%
50%
40%
30%
20%
RAP
RCA
10%
0.75" Max. Nominal
0%
0.01
0.1
1
10
100
Sieve size (mm)
Figure 3-6 Comparison of grain size distribution of RAP and RCA with HDOT
specification requirements for 0.75-inch
3.2.1.3 Compaction Curve
RAP and RCA were compacted in accordance with the Modified Proctor Test
(ASTM D1557 – Method C).
In both RCA and RAP, water was not readily
absorbed by the materials especially with the wetter samples, wherein water was
observed to seep from the bottom of the mold.
This problem was more
pronounced with RAP since it has a lower absorption and contained very little
fines. With RCA at higher moisture contents, water sometimes collected at the
surface. Figures 3-7 and 3-8 show the compaction curves for RAP and RCA,
respectively.
157
1000
Dry Density (pcf)
113
112
111
110
2%
3%
4%
5%
6%
Moisture Content (%)
Figure 3-7 RAP compaction curve
110
109
Dry Density (pcf)
108
107
106
105
104
103
102
9%
10%
11%
12%
13%
14%
15%
Moisture Content (%)
Figure 3-8 RCA compaction curve
158
16%
17%
18%
3.2.1.4 Friction Angle
Selvarajah (2009) determined the friction angles of RAP and RCA used in these
experiments in a direct shear box having a diameter of 2.4 inches (61.4 mm).
Due to the limited size of the shear box, Selvarajah used gradations that were
parallel to the ones shown in Figure 3-6 with a maximum size of 0.2 inches (4.75
mm). Several researchers have found that a finer parallel gradation gave similar
friction angles to the same geological material with a coarser gradation provided
the mineralogy, hardness of grains, particle shape, and particle roughness do not
vary with particle size (Varadarajan et al., 2006, Varadarajan et al., 2003,
Verdugo and de la Hoz, 2007, Cambio and Ge, 2007). Direct shear tests were
conducted on samples compacted to a density and moisture content similar to
the density that the materials were compacted to in the bin experiments. Based
on Selvarajah‘s data, it was inferred that the friction angle of RCA and RAP were
50.7˚ and 42.8˚, respectively. These values are within 3 degrees of Rathje et
al.'s (2002) values.
The friction angle of RCA is larger than that of RAP. This can be attributed to the
fact that RCA particles have rough surfaces, which require more load to move
the particles relative to each other. Also, hydration of cement in RCA may bind
the particles and hinder their movement. On the other hand, the RAP particles
are more likely to slip within themselves because of the asphalt binder.
159
3.2.2 Calibration of Instruments
Calibration offsets increase the accuracy of the nuclear gauge‘s readings.
According to the Troxler Operator‘s Manual (2009), there are three types of
offsets that can be used: wet density offset, trench offset, and moisture offset.
The wet density offset should be used when the density does not range between
70 to 170 pcf. A trench offset should be provided when using the nuclear gauge
within two feet of a vertical wall or structure. The moisture offset should be used
on geomaterials containing hydrogen atoms present in a form other than water.
To calculate the moisture offset factor, k, the following equation is used
k
%wlab %wgauge
1000
100 %wgauge
(3.3)
where %wlab = water content in % measured using an oven and %wgauge = water
content in % measured using the nuclear gauge. Attention should be paid to the
sign of the moisture offset factor.
On each day prior to using the nuclear gauge, it was necessary to run a standard
count to ensure the gauge readings are reliable. Also, before obtaining readings
in the bin, a trench offset is obtained.
The TDR and FlexiForce® Sensors were calibrated prior to use. The effect of
three varying drop heights on stiffness was investigated prior to use of the
PFWD.
It was found that the various drop heights yielded similar stiffness
values.
It is expected that stiffness non-linearity will manifest in softer
geomaterials rather than in the stiffer base/subbase type of materials that are
addressed in this research.
160
3.2.3 Bin Set-up and Compaction
FlexiForce® sensors were attached to the inside wall of the bins at 0.25, 1.25
and 2.25 feet above the bottom to measure the compaction-induced lateral
stress. In addition, a fourth sensor was placed at the bottom center of the bin to
measure the vertical stress. The sensors were attached using scotch tape but
care was made not to scotch tape the sensing element itself. The sensors and
transmitters connected to the sensors are shown in Figure 3-9.
The cylindrical bins were marked every six inches to coincide with the intended
lift thickness.
Figure 3-10 shows a profile view of the bin used in the
experiments.
Figure 3-9 Sensors attached to bin (Left) and sensors connected to transmitters
(Right)
161
Figure 3-10 Profile view of bin
Prior to compaction, the desired amount of material per lift was weighed and the
water content measured.
Values of dry density and water content from the
nuclear gauge and TDR can then be compared to these ―true‖ values.
The
recycled material and water were thoroughly combined in a concrete mixer as
shown in Figure 3-11.
162
Figure 3-11 Electric concrete mixer used to blend RAP with water and RCA with
water
The moist material was then poured into the bins and compacted using a Bosch
Brute Breaker Hammer Model 11304 accessorized with an 8-inch by 8-inch steel
tamper plate (Figure 3-12). A 2 ½-foot diameter, ¾-inch thick wood base was
used between the compactor and the geomaterial to spread the compactive force
over a wider area and to create a flat finished surface.
The RAP and RCA were compacted in six 6-inch lifts yielding a finished height of
three feet. After each lift was compacted, GeoGauge, PFWD, nuclear gauge and
TDR tests were performed in that order. The rationale for this sequence is to
work from the least to the most destructive tests in the interest of sample
preservation. Figure 3-13 shows a plan view of the bin and the respective test
areas. At least five readings of dry density and water content for the nuclear
gauge and TDR tests and five for the Geogauge and PFWD stiffness were
recorded for each layer and for the top lift during post-compaction testing.
163
Figure 3-12 Bosch hammer with tamper plate and wood base
Figure 3-13 Plan view of test locations in bin
Dial gauges were attached to the outside wall of the bins at one and two feet
above ground (Figure 3-14) to: (1) measure the bin wall deflections as the
164
material was compacted; (2) assess if any post-compaction deflections would
occur as a result of creep; and (3) allow for more accurate volumes to be
calculated when estimating the in-place densities. Sandbags were placed at the
base of the dial gages to aid stability. The dial gauges were read after each lift
and also periodically for about two months after reaching the three-foot height.
Figure 3-14 Dial gauges
165
A list of instruments used and the desired measurements are summarized below.
Instrument
Nuclear Moisture Density Gauge
Time Domain Reflectometry
GeoGauge
Portable Falling Weight Deflectometer
FlexiForce® Sensors
Dial Gages
Measurement
Moisture Content and Density
Moisture Content and Density
Stiffness/Elastic Modulus
Stiffness/Elastic Modulus
Lateral Pressure
Wall Deflection
3.2.4 Post-compaction Measurements
Another phase of this experiment was to evaluate if the properties changed or
the material crept with time over a post-compaction period of approximately two
months. Table 3-1 summarizes the tests performed and the times of testing.
Table 3-1 Experiment timeline
Days after compaction
when readings were
Instrument
taken
RAP
RCA
0
0
5
5
11
9
Nuclear Gauge/TDR/
GeoGauge/PFWD/
15
FlexiForce® Sensors
25
19
43
37
63
57
FlexiForce® Sensors
85
77
For the nuclear gauge test, it was attempted to use the same direct transmission
hole when testing the top lift during this period except if the hole caved in, in
which case, a new one was created.
For the TDR test, the probes were driven and left in place immediately after
compaction for the entire post-compaction duration.
166
3.3 DENSITY EVALUATION USING NUCLEAR GAUGE AND TIME DOMAIN
REFLECTOMETRY
3.3.1 Introduction
The sand cone and rubber balloon methods for determining in situ dry unit weight
and moisture content require drying samples in an oven. Consequently, they do
not provide instantaneous moisture content readings, which is an important
element in earthwork construction. Two methods that instantaneously determine
the dry unit weight and moisture content include the nuclear gauge (ASTM
D6938) and TDR (ASTM D6780).
3.3.1.1 Previous Studies on the Nuclear Gauge on RCA and RAP
The applicability of the nuclear gauge on RCA and RAP has been investigated by
Rathje et al. (2002). They found that the RCA moisture content from the nuclear
gauge was about 20% larger than oven dried values while the RAP moisture
content readings from the nuclear gauge were almost three times the oven dried
readings (Rathje et al., 2002). This can be attributed to the fact that hydrogen
atoms can be found not only in water but also in the cement and possible
admixtures in RCA and in the asphalt in RAP (Rathje at al., 2002).
3.3.1.2 Previous Studies on Time Domain Reflectometry
Previous studies on the use of TDR on RAP and RCA were not found. Instead
this section focuses on the background theory, calibration of the TDR and the
test procedure.
In the TDR method, an electromagnetic wave pulse is sent
through probes embedded in a geomaterial. Reflections of the pulse caused by
the top of the tested material and by the end of the probe are recorded using an
oscilloscope.
The oscilloscope plot is then used to provide the apparent
167
dielectric constant (Ka) and bulk electrical conductivity (ECb) of the geomaterial.
Topp et al. (1980) discovered the famous relationship between Ka and volumetric
water content () that initially facilitated its use in mostly agricultural applications.
4.3106 Ka3 5.5 104 Ka2 2.92 102 Ka 5.3102
(3.4)
Applicable to a large number of different soils in the field, this relationship was
established
on the basis that large differences exist between Ka for soil solids
and Ka for water, and that Ka for wet soil depends largely on the volumetric
moisture content.
Then Siddiqui and Drnevich (1995) of Purdue University
developed relationships between the apparent dielectric constant (K a) and bulk
electrical conductivity (ECb) with water content and with dry unit weight that made
the TDR useful for geotechnical applications.
Apparent Dielectric Constant
According to Drnevich et al. (2003), the apparent dielectric constant is the real
portion of the complex dielectric permittivity. The imaginary portion takes into
account the electrical loss while the real portion represents the amount of energy
stored in the material. Only the real portion is relevant in determining moisture
content and dry unit weight.
A typical waveform is shown in Figure 3-15. Two reflections are observed: one
when the pulse first contacts the soil surface and another when the pulse
reaches the tip of the probe. Ka is measured using the following equation
L 2
a
K a
L
p
(3.5)
168
where Lp = length of center probe that is in the soil and La = apparent length =
scaled horizontal distance between the first and second reflections (Yu &
Drnevich, 2002).
Figure 3-15 Parameters to determine Ka (Durham Geo Slope Indicator, 2003)
As an alternative to Equation 3.5, Drnevich et al (2003) proposed the following
square root relationship between and Ka as equivalent to Topp‘s equation:
b Ka a
(3.6)
provided constants a and b had values of 0.1841 and 0.1181, respectively.
However, Abdulla et al. (1988) and Ponizovsky et al. (1999) determined that soil
density also influences the dielectric constant.
This led Siddiqui (1995) to
combine the gravimetric moisture content and dry densities in the following
equation:
Ka
w
a bw
d
(3.7)
169
where d = soil dry density, w = density of water and a and b are constants.
Bulk Electrical Conductivity
In principle, the electrical conductivity (ECb) is the property of a material that
causes an electrical signal to dissipate as it travels through that material.
Therefore, the TDR signals are attenuated due to a material‘s EC b, which can
also be measured using the same waveform for determining K a as follows (Yu &
Drnevich, 2002 – see Figure 3-16):
EC b
1 Vs
1
C
V f
(3.8)
Figure 3-16 Parameters to determine ECb (Yu and Drnevich, 2004)
where Vs = source voltage = two times the step voltage, Vf = final voltage level
and C is based on how the probes are configured as follows:
C
2L p Rs
d
ln o
di
(3.9)
170
where Rs = internal resistance of the pulse generator, do = outside diameter of
the conductor, and di = inside diameter of the conductor (Giese and Tiemann,
1975).
Yu and Drenvich (2004) proposed the following empirical relationship between
ECb, moisture content and dry density:
EC b .
w
c dw
d
(3.10)
where c and d are constants.
Calibration
Prior to using the TDR, the equipment should be calibrated for each geomaterial
that it will be used on. Calibration for RAP and RCA was facilitated by running
Proctor Tests.
The standard TDR equipment includes a 4-inch diameter
compaction mold. However, the gradation of RAP and RCA precluded the use of
a 4-inch diameter mold because greater than 20% of the material is retained on
the 3/8-inch sieve. Method C of ASTM D1557, which allows more than 20%
retained on the 3/8-inch sieve and less than 30% retained on the ¾- inch sieve,
had to be used, but this method requires a 6-inch-diameter compaction mold.
Therefore, such a mold with a non-conductive base had to be custom ordered
from the manufacturer to perform the calibration.
During compaction, a regular steel base was used. During calibration, the base
was switched to the non-conductive variety as shown in Figure 3-17. Then, a
plastic guide was attached to the top of the mold to help direct the driving of a rod
in the middle with the aid of a rubber mallet or non-steel hammer. The plastic
guide is removed and the top edge of the mold is cleaned to ensure proper
171
electrical contact between the mold and mold collar. The mold collar is then
placed on the mold followed by the coaxial head ensuring that the center rod is in
contact with the center of the coaxial head (see Figure 3-17 right)
Figure 3-17 Center rod guide and non-conductive base (Left) and coaxial head
and mold collar on compaction mold (Right)
For each compaction sample, Ka and ECb are measured and recorded.
Calibration constants a and b can be found using Equation 3.7 by plotting
Ka
w
against water content (Figure 3-18). The slope and y-intercept are b and
d
a, respectively. Constant a is related to the dry density and apparent dielectric
constant of the geomaterial while b is related to the dielectric constant of the pore
fluid (Drnevich et al., 2003).
Constants c and d are obtained by plotting
EC b
w
against water content
d
(Figure 3-19). The slope and y-intercept are d and c, respectively. The constant
and
c is related to the dielectric conductivity
dry density while d is related to the
material type and pore fluid properties (Drnevich et al., 2003).
172
y = 0.1205x + 0.9056
R2 = 0.956
√Ka *(w/d)
1.6
1.4
1.2
1.0
2
3
4
5
6
Moisture Content (%)
(a)
3.0
y = 10.695x + 0.6361
R2 = 0.9186
√Ka *(w/d)
2.5
2.0
1.5
8%
10%
12%
14%
16%
Moisture Content (%)
(b)
Figure 3-18 Constants a and b for (a) RAP and (b) RCA
173
18%
0.06
y = 0.0052x + 0.0261
R2 = 0.9406
√ECb * (w/d)
0.05
0.04
0.03
2
3
4
5
6
Moisture Content (%)
(a)
0.15
√ECb * (w/d)
0.10
y = 0.9501x - 0.0386
R2 = 0.7988
0.05
0.00
9%
12%
15%
Moisture Content (%)
(b)
Figure 3-19 Constants c and d for (a) RAP and (b) RCA
174
18%
From equations 3.7 and 3.10, it can be seen that Ecb and Ka are related as
follows (Drnevich et al., 2003):
ECb
b c a d d d
Ka
b
w b
(3.11)
which has the same form as:
ECb f g K a
(3.12)
Therefore, f is related to constants a, b, c, d and dry density. Even though f is
related to dry density, it is referred to as a constant by Yu and Drnevich (2004).
Constant g is related to b and d. By plotting
EC b against
K a (Figure 3-20),
the slope and y-intercept are g and f, respectively.
Table 3-2 summarizes the calibration constants for different types of soils.
According to Yu and Drnevich (2004), values of a are typically between 0.7 and
1.85 and values of b are typically between 7 and 12. Typical values for c, d, f,
and g have not yet been determined (Runkles et al., 2006).
175
0.11
y = 0.0423x - 0.0208
√ECb
R2 = 0.9052
0.09
0.07
0.05
2.0
2.5
3.0
√Ka
(a)
0.3
y = 0.0854x - 0.1483
R2 = 0.8991
√ECb
0.2
0.1
0.0
2.5
3.0
3.5
4.0
√Ka
(b)
Figure 3-20 Constants f and g for (a) RAP and (b) RCA
176
4.5
Table 3-2 Summary of TDR calibration constants
Ottowa Sand
Florida Sands
(Max)
Florida Sands
(Min)
Ottowa Sand
(Illinois)
Sandy Soil
(Florida)
Brown County
Clay (Ohio)
Glacial Till
(Indiana)
Loess
(Mississippi)
Lean Clay
(Mississippi)
Buckshot Clay
(Mississippi)
USCS
Classification
a
b
c
d
f
g
Reference
SP
0.93
9.21
-
-
-
-
Drnevich et al.,
2003
SP
1.080
10.15
0.0593
0.801
0.0285
0.0836
SP
0.875
7.48
0.0036
0.149
-0.0923
0.0210
SP
1.03
7.83
-
-
-
-
SP
1
8.45
-
-
-
-
CL
0.91
8.84
-
-
-
-
SM
1.02
9.06
-
-
-
-
ML
1.21
7.95
-
-
-
-
CL
1.3
7.93
-
-
-
-
CH
1.22
10.97
-
-
-
-
Runkles et al.,
2006
Durham, 2005
Calibration Constants Determined in this Study
Table 3-3 summarizes the constants for RAP and RCA obtained in this study.
Table 3-3 Soil specific calibration constants for this study
RCA
RAP
USCS
Classification
a
b
c
d
f
g
GP
GW
0.6361
0.905
10.695
12.06
-0.0386
0.026
0.9501
0.5213
-0.1483
-0.02
0.0854
0.0422
For the most part, the calibration constants for RCA and RAP are comparable to
values in the literature. Constant a for RCA was slightly outside the typical range
of values.
Knowing the calibration constants a, b, c and d, and combining equations (3.7)
and (3.10), the dry density and moisture content can be estimated as follows
(Siddiqui and Drnevich, 1995):
177
w
c K a a EC b
b EC b d K a
d
d K a b EC b
ad cb
(3.13)
w
(3.14)
Test Procedure
There are two methods for running the TDR tests (ASTM D6780) - the Two-Step
and One-Step Method. In the Two-Step Method, the soil is tested in situ. The
second step is to calibrate the TDR. This is performed by excavating a sample
quickly and testing it in a mold on site so as to minimize drying.
In the One-Step Method, the calibration is performed in the laboratory prior to
TDR testing in the field. The name ―One Step Method‖ is not accurate because
there are really two steps to this procedure. What the ―one step‖ refers to is that
there is only one step in the field; the calibration is performed in the laboratory.
The One Step Method is followed in this research.
Steps to run the TDR test in the field are as follows:
(a) Drive four spikes in a coaxial configuration using the guide provided
(Figure 3-21 left);
(b) Remove the guide (Figure 3-21 right);
(c) Place the coaxial head on the four probes ensuring good contact between
them (Figure 3-2b);
(d) Connect the PDA to the TDR which in turn is connected to the coaxial
head (Figure 3-2a); and
(e) Measure Ka. It will be explained later on that ECb is not used at all in the
field test.
178
Figure 3-21 Template (Right) and probes inserted in RAP (Left)
Field measurements (denoted with subscript f) of Ka (Ka,f) must be adjusted for
temperature differences that exist between the laboratory calibration and the field
measurements. The adjusted value is typically standardized to 20ºC. Therefore,
the field value Ka,f is corrected as follows:
Ka,20C Ka, f TCF
(3.15)
where TCF = temperature correction factor using the following equations:
TCF 0.97 0.0015Ttest,C
TCF 1.10 0.005Ttest,C
for a cohesionless geomaterial
for a cohesive geomaterial.
These equations are applicable if the testing temperature, T test,˚C, is between 4
and 40ºC.
Then ECb,adj is determined using Ka,20ºC as follows:
ECb,adj ( f g K a,20C )2
(3.16)
where f and g are determined from Figure 3-20. Then, the water content and dry
density
are calculated as follows:
179
w
c K a,adj a EC b,adj
(3.17)
b EC b,adj d K a,adj
d
d K a ,adj b EC b ,adj
(3.18)
ad cb
It can be seen that the ECb measured in the field is not used at all in the
calculation of dry density and moisture content.
For this experiment, no
temperature adjustment factor was applied because the calibration and bin
measurements were performed in the soils laboratory at the same temperature
and using the same water source (tap water).
3.3.2 Test Results
3.3.2.1 Actual Dry Density
The actual dry density per lift was calculated using the measured wall
deflections. An equation for the deflected bin wall was derived by using the two
deflection measurements and by assuming the following boundary conditions:
slope and deflection at the bottom and the slope at the top of the bin = zero.
The six deflected profiles after compaction of the six different RCA lifts are shown
in Figure 3-22. It can be seen that the deflected profiles for lifts 2 through 6 are
almost identical. The deflections after compacting Lift 1 are much smaller. Only
the figure for RCA is presented. The deflected profile for RAP is not shown
because the dial gauges were accidentally kicked during compaction.
180
Figure 3-22 Deflection profile based on dial gauge readings
181
To determine the dry densities for each lift, the respective equations for the defected
wall profiles were integrated to determine each lift volume. The dry densities can be
determined with precision because the actual material weight was determined and the
moisture content measured for each lift.
3.3.2.2 Measured Moisture Content
The nuclear gauge and TDR moisture contents for RAP and RCA are plotted versus the
actual values in figures 3-23 and 3-24, respectively. The overall average ratios of the
nuclear gauge/oven dry and TDR/oven dry moisture contents are summarized in Table
3-4. Over the six lifts, the nuclear gauge over-predicted the moisture contents of RCA
and RAP on average by 14% and 55%, respectively, as compared to the oven dried
values. TDR moisture contents for RAP are on average higher than the oven dried
values by 5% while TDR moisture contents for RCA are 14% lower than the oven dried
moisture contents.
Table 3-4 Moisture content summary
average
RAP
RCA
1.55
1.14
wNG/wOVEN
standard
deviation
0.17
0.09
COV
(%)
0.11
0.08
182
average
1.05
0.86
wTDR/wOVEN
standard
deviation
0.08
0.04
COV
(%)
0.08
0.05
Nuclear Gauge/TDR Moisture Content (%)
8
7
6
5
Nuclear Gauge
4
TDR
Line 1:1
3
3
4
5
6
7
8
Oven Measured Moisture Content (%)
Figure 3-23 RAP moisture content comparison
20
Nuclear Gauge/TDR Moisture Content (%)
19
18
17
16
15
14
13
12
Nuclear Gauge
TDR
11
1:1 Line
10
10
11
12
13
14
15
16
17
18
Oven Measured Moisture Content (% )
Figure 3-24 RCA moisture content comparison
183
19
20
3.3.2.3 Measured Dry Density
The nuclear gauge and TDR dry density for RAP and RCA are plotted versus the actual
values in figures 3-25 and 3-26, respectively. Table 3-5 summarizes the average of the
ratios of the measured dry densities with the actual values along with some statistics.
For RAP, the nuclear gauge and TDR points hover around the 1:1 line indicating that
the measured dry unit weights are on average close to the actual. For RCA, the nuclear
gauge dry unit weights are on average close to the actual values but the TDR dry unit
weights are relatively constant.
Nuclear gauge/TDR Dry Density (pcf)
116
114
112
110
108
106
104
Nuclear Gauge
TDR
1:1 Line
102
100
100
102
104
106
108
110
112
Actual Dry Density (pcf)
Figure 3-25 RAP dry density comparison
184
114
116
Nuclear Gage/TDR Dry Density(pcf)
110
108
106
104
102
100
98
96
94
Nuclear Gauge
TDR
1:1 Line
92
90
90
95
100
105
110
Actual Dry Density (pcf)
Figure 3-26 RCA dry density comparison
Table 3-5 Dry density summary
average
RAP
RCA
1.00
0.97
dNG/dACTUAL
standard
deviation
0.05
0.05
COV
(%)
0.05
0.05
dTDR/dACTUAL
standard
average
deviation
1.03
0.04
1.01
0.04
COV
(%)
0.04
0.04
Due to the TDR‘s poor prediction of the dry unit weight of RCA, an attempt was made to
mathematically recreate the RCA compaction curve using the TDR calibration constants
and equations 3.12, 3.13 and 3.14.
The following expression for dry density as a
function of moisture content can be derived:
d
f w
w(d bg ) c ag
(3.19)
185
From Figure 3-27, it is observed that equation 3-19 cannot recreate a classical bellshaped compaction curve for all practical ranges of moisture content (i.e; dd/dw can
never be zero to yield a maximum d).
3.3.2.4 Post-Compaction Moisture Content and Density
Following compaction of the top lift, the RCA and RAP were tested to see if the moisture
content and density changed with time.
Moisture Content
With respect to the variation of moisture content with time, the following observations
are offered:
1. The Nuclear Gauge consistently provided higher moisture contents than the TDR
(Figure 3-27 and 3-28).
Figure 3-27 RAP moisture content versus time
186
Figure 3-28 RCA moisture content versus time
2. After 63 days, the RAP oven dried moisture contents are lower than those during
compaction. The fact that RAP has a low absorption, contained less fines and
standing water was observed at the bottom of the bin when it was emptied
suggests that water flowed down from the top. Evaporation was minimized by
covering the bins with lids as shown in Figure 3-29.
187
Figure 3-29 Bin covered with lid
3. The RCA moisture content appeared relatively constant for the first 37 days
(Figure 3-28). Thereafter, both the Nuclear Gauge and TDR registered a drop in
moisture content. The oven-dry moisture content also dropped slightly after the
57-day post-compaction period. No standing water was observed at the bottom
of the bin when it was emptied. Again, the bin was covered with a lid during the
post-compaction period. If the lid was effective in minimizing evaporation, the
drop in moisture content may be a result of hydration in the RCA since the
crushing process most likely exposed unhydrated cement leading to additional
pozzolanic reaction upon wetting (water was added during mixing).
188
Density
With respect to the change of dry unit weight with time, the following observations are
offered:
1. Ten days after compaction, both the nuclear gauge and TDR dry densities for
RAP remained relatively constant (Figure 3-30).
Figure 3-30 RAP dry density versus time
2. Figure 3-31 shows that the TDR dry density for RCA remained constant
throughout the entire post-compaction period while the nuclear gauge dry density
increased with time over the same period. The dial gauges did not register any
bin wall movements for both RAP and RCA during the post-compaction period.
Thus, the dry density should theoretically not change. Based on this, the nuclear
gauge dry density values for RCA over time are questionable.
189
Figure 3-31 RCA dry density versus time
3.3.3. Summary and Conclusions
The objectives of this chapter were to: (a) compare the nuclear gauge and TDR
methods of estimating moisture content and dry density of RAP and RCA with actual
values by compacting these materials in six 6-inch-thick lifts in 3-foot diameter bins; (b)
assess the variation of moisture content and dry density in the top lift over a postcompaction period of two months; and (c) assess if the materials crept during the post
compaction period by monitoring the bin wall movements with time.
conclusions are offered:
190
The following
1. The nuclear gauge consistently provided higher moisture contents than actual for
both RAP and RCA. This can be attributed to the fact that in addition to being
present in free water, hydrogen atoms also exist in the cement paste in RCA and
in asphalt in RAP. This suggests the need for nuclear offsets to be calibrated
prior to use with these materials. The nuclear gauge moisture offset factors are
estimated to be -23.3 and -13.8 for RAP and RCA, respectively.
2. The dry density from the nuclear gauge on average appears relatively reliable.
However, this may be fortuitous because the nuclear gauge actually provides a
measure of the moist unit weight. The dry unit weight is then derived using the
overly predicted moisture content.
3. The TDR water contents for RAP and dry densities for RAP and RCA seemed
reasonably accurate on average. However, the TDR water contents for RCA
were underpredicted.
4. Attempts to replicate a bell-shaped compaction curve using the experimentallyderived calibration constants and the formulation published by Yu and Drnevich
(2004) were not successful. This limitation poses a question as to whether the
TDR is able to overall yield reliable results and its formulation should be reevaluated.
5. With respect to the variation of moisture content with time, the following
observations are offered:
a. The nuclear gauge consistently provided moisture contents higher than
the TDR.
191
b. The moisture content of the top lift in RAP initially decreased with time.
After 11 days, the moisture content remained constant.
c. The RAP oven dried water contents after 2 months are lower than those at
the end of compaction due to downward flow of water since RAP
contained little fines, does not have a high absorption and standing water
was observed at the bottom of the bin when it was emptied. During the
post compaction period, the bins were covered with lids to minimize
evaporation.
d. The RCA moisture content appeared relatively constant for the first 37
days. Thereafter, both the Nuclear Gauge and TDR registered a drop in
moisture content. Oven-drying also indicated that the moisture content
decreased during the post-compaction period. The fact that there was no
standing water observed at the bottom of the RCA bin suggests there was
little downward flow.
The decrease in moisture content suggests that
hydration of the water added during compaction due to pozzolanic
reaction most likely occurred during this period.
6. With respect to the change of dry unit weights with time, the following
observations are offered:
a. The nuclear gauge dry density for RAP is higher than the TDR dry density.
b. Ten days after compaction, both the nuclear gauge and TDR dry densities
for RAP remained relatively constant.
c. The TDR dry density for RCA remained constant throughout the entire
post-compaction period while the nuclear gauge dry density increased
192
with time. The dial gauges did not register any bin wall movements for
both RAP and RCA during the post-compaction period. Thus, the dry
density should theoretically not change. Based on this, the nuclear gauge
dry density values over time are questionable.
193
3.4 STIFFNESS EVALUATION USING PORTABLE FALLING WEIGHT
DEFLECTOMETER AND GEOGAUGE
3.4.1 Introduction
Traditionally, quality control/quality assurance of earthwork compaction is based on dry
density and moisture content. However, with the advent of the MEPDG, there has been
a recent push to use stiffness instead of dry density and moisture content. Dry density
and moisture content are not engineering properties; they provide little insight on the
material‘s deformation characteristics. On the other hand, the stiffness of the base,
subbase and subgrade are increasingly recognized as being important input parameters
for determining the thickness of pavement sub-layers.
The California Bearing Ratio and plate load tests have been utilized to measure the
strength or stiffness of a geomaterial for use in pavement design. However, these tests
require large reaction forces and cumbersome equipment (Kim et al. 2007) making
them time consuming to perform. There are several portable devices that can be used
to provide a measure of a geomaterial‘s surface stiffness. They can be divided into
three categories. The first category consists of impact devices that actually penetrate
into the ground. They include:
1. Clegg Impact Hammer (Steinert et al., 2005);
2. Dynamic Cone Penetrometer (Illinois Department of Transportation, 2005); and
3. PANDA dynamic cone penetrometer (Langton, 1999).
The second category consists of devices that send a shock wave to the ground. The
stiffness is calculated based on load and displacement measurements (using velocity
transducers or accelerometers). These devices include:
194
1. Loadman portable falling weight deflectometer (Steinert et al., 2005);
2. German Dynamic Plate (Alshibli et al., 2005);
3. PRIMA 100 portable falling weight deflectometer or PFWD (Steinert et al., 2005,
Alshibli et al., 2005);
4. Dynaplaque II (Ruban, 2002);
5. Portable Seismic Property Analyzer (Celaya and Nazarian, 2006); and
6. GeoGauge (Humbolt Manufacturing Co., 2007).
According to Tutumluer (2004), the first two devices rely on physics (height and weight
of the drop load) to estimate the force rather than a load cell, which led Tutumluer to
conclude that they are deficient in accuracy.
A third category consists of burying sacrificial sensors in the compacted ground to
monitor the growth in amplitude of pressure waves.
Once the growth ceases, the
compaction is considered complete and the next lift can proceed. An example of this
device is the Soil Quality Indicator (SQI).
This section focuses on two devices from the second category: the PRIMA 100 PFWD
and GeoGauge to measure the stiffness of RAP and RCA in the bin experiments.
3.4.2 Literature Review
Density and Stiffness
According to Fiedler et al. (2000) and Ooi and Pu (2003), there is no direct relationship
between dry unit weight and stiffness. A material having a particular dry unit weight can
have two values of stiffness. In addition, the maximum stiffness does not necessarily
occur at the maximum dry density in compacted cohesive soils; they can occur dry of
optimum (Lenke et al, 2001 and Ooi & Pu, 2003). In general, the stiffness decreased as
the moisture content increased and the dry density decreased.
195
PFWD
Developed by Keros Technology and Carl Bro Pavement Consultants of Denmark, the
Prima 100 PFWD consists of a falling mass that impacts a load plate, which in turn
deforms into a geomaterial. The mass is dropped by pressing a release trigger seen in
Figure 3-32 (left). The mass falls along a guide pole onto rubber buffers seen in Figure
3-32 (right). A load cell in the instrument measures the force that is imparted by the
falling mass and a geophone measures the surface velocity.
The PFWD can be
accessorized with up to three additional geophones to measure the ground response. If
all three geophones are used, then the offset of the geophones with respect to the
center geophone are typically 207 mm and 407 mm (8 and 16 inches). Additional
geophones were not used in these experiments.
Figure 3-32 PFWD release trigger (Left) and drop weight, rubber buffers, velocity
transducer (Right)
There are several falling mass, drop height and plate diameter configurations. The
three falling mass choices include 22, 33 and 44 lbs (10, 15, 20 kg). The drop heights
range between 0.4 and 33.5 inches (10 to 850 mm). The choices of plate diameters
196
include 3.9, 7.9, and 11.8 inches (100, 200, 300 mm) (Steinert et al., 2005). In these
experiments, the following were used: a 22-lb-mass, a 66-cm-drop height and a 300mm-diameter load plate.
The elastic modulus is calculated from the solution for the deflection of a uniformly
loaded circular plate on a linear elastic half space (Florin, 1959) as follows:
E PFWD
2(1 2 ) R
(3.20)
c
where applied stress, R = plate radius, = Poisson‘s ratio of the geomaterial, c =
deflection at the center of the plate.
Steinhert et al. (2005) studied the effect of repeated drops on the stiffness at one
location. They found that the first measurement was typically smaller than subsequent
measurements, and recommended that the first value should not be included in the final
stiffness average. They also studied the effects of the plate size and drop weight and
found that when using the 15 or 20 kg drop weight, the stiffness did not change very
much with different plate diameters.
Lin et al. (2006) also studied the effect of varying drop heights on stiffness. Using four
drop heights and two plate diameters, they found that the different drop heights had
very little effect on stiffness.
To determine the quality of the PFWD results, Fleming et al. (2001) suggested that the
deflection-time history of each drop be assessed. Figure 3-33 shows that a high quality
test should have no deflection at time zero, should increase to a maximum value
followed by a decrease, and should have little to no deflection at the end of the pulse.
197
Figure 3-33 High quality PFWD reading (Fleming et al., 2009)
Figure 3-34 High rebound PFWD reading (Fleming et al., 2009)
Figure 3-34 shows the deflection at the end of the pulse going in an opposite direction
instead of returning to zero.
This type of signal can be obtained if the instrument
bounces off the ground upon impact or if there is excess water in the geomaterial. .
198
Figure 3-35 Effect of subsequent PFWD drops (Fleming et al., 2009)
Figure 3-35 shows the changes in the deformation-time histories upon successive drops
at the same spot. Both the maximum deflection and the final deflection decrease with
increasing number of blows.
The above graphs provide a means of evaluating which readings should or should not
be used. For the bin experiments, each PFWD drop was plotted. For example, Figure
3-36 contains a plot of a series of readings obtained for the first RCA lift. Among the six
drops, it can be seen that the first drop should be considered erroneous.
During the
second drop, the instrument may have bounced off the ground. Drops 3 through 6 are
considered valid.
199
Pulse Time (ms)
-50
0
5
10
15
20
25
30
35
40
0
Deflection (mm)
50
Drop 1
100
150
200
250
Drop
Drop
Drop
Drop
Drop
Drop
300
350
1
2
3
4
5
6
400
Figure 3-36 RCA PFWD test quality assessment
GeoGauge
The GeoGauge was developed by the FHWA and the U.S. Department of Defense
Advanced Research Programs Administration based on the principles of a U.S. military
device for detecting land mines using acoustic and seismic detectors. According to
Fiedler et al. (1998), the same theory and technology employed in this device can be
used to assess the compaction of earthworks.
The GeoGauge is 11 inches in diameter and 10 inches tall.
It is placed on a
geomaterial by means of a ring-shaped foot that protrudes from the bottom center
(Figure 3-37).
200
Figure 3-37 Schematic of GeoGauge (GeoGauge User Guide, 2007)
The foot has an outer diameter of 4.5 inches, an inner diameter of 3.5 inches and a
thickness of 0.5 inches and is powered by six D-cell batteries. In the GeoGauge is an
electro-mechanical shaker, that is set to vibrate at 25 different frequencies varying from
100 to 196 Hz. The vibrations cause very small displacement (about 0.0005 inches). At
each frequency, the stiffness (K) of the material is determined from the force in the load
cell and the displacement from the transducers. Then the elastic modulus is computed
as follows (Egorov, 1965):
E K
(1 2 )
1.77R
(3.21)
201
where E = elastic modulus, K = Geogauge stiffness, R = radius of ring shaped foot (2.25
inches) and = Poisson‘s Ratio. It is important to have at least 60% of the area of the
foot in direct contact with the geomaterial. Each test takes about 1.5 minutes.
Previous Studies on Cement Stabilized Soils
Using the Prima 100 PFWD and GeoGauge, Abu-Farsakh et al. (2004) measured the
stiffness of a mixture of clay and either two or four percent cement for about 2 weeks.
In general, the elastic modulus increased to a maximum because of cementation and
decreased thereafter. One reason cited for the decrease is shrinkage cracks.
Alshibli et al. (2005) performed a similar study on the stiffness over a period of time,
using 2, 4, 6 or 8 percent cement and clay. Similar trends were found in this and the
previous study where the stiffness of the material measured by the GeoGauge and
PFWD decreased after a certain point probably also due to shrinkage cracks. It is
interesting to note that field measurements are typically made immediately after
compaction and before shrinkage cracks have had a chance to form.
Zone of Influence
Associated with the PFWD and GeoGauge is a zone of influence or the depth in the
geomaterial at which the imparted stress becomes negligible. If the geomaterial below
a layer that is being tested has a different stiffness and falls within the zone of influence,
then the PFWD or GeoGauge will provide a composite stiffness value. Therefore it is
important to establish the zone of influence for both instruments so that the modulus
can be associated with the appropriate lift thickness. There have been several studies
to determine the zone of influence.
202
Nazzal (2002) determined the zone of influence for both the PFWD and GeoGauge in
two test boxes that were 36 inches wide, 72 inches long and 36 inches deep, one box
containing compacted clay and the other compacted Florolite, more commonly known
as plaster of Paris.
The clay had a smaller stiffness than the Florolite.
In his
experimental set-up, a 9- to 12-inch-deep, 12-inch-diameter plastic cylindrical mold was
placed at the center of the test box. Then, the material was compacted around the
plastic cylindrical mold. The plastic cylindrical mold was subsequently removed leaving
a cylindrical opening. Then the material to be tested is compacted with a standard
Proctor hammer in the cylindrical void. After each layer was compacted, the PFWD and
GeoGauge were used to determine the stiffness of each layer. The variation of stiffness
versus elevation was plotted and Nazzal estimated the zone of influence by determining
the depth at which the stiffness began to level off. Nazzal‘s results are shown in Table
3-6. It should be noted that the PFWD tests were conducted using a base diameter of 8
inches (about 200 mm) and a drop weight of 22 lb (10 kg). The drop height used in his
study was not stated.
Sawangsuriya et al. (2002) determined the zone of influence of the GeoGauge in a 1.2
m x 1.2 m x 1.2 m box. Their procedure was similar to Nazzal‘s. They used three
different materials with different stiffnesses. Three different sized cylindrical molds were
placed in the middle of the box. The results of Sawangsuriya‘s experiments are also
summarized in Table 3-6.
203
Table 3-6 Summary of zone of influence from the literature
Zone of
Test Configuration
Instrument
Influence
Author (Date)
(Material Tested)
(in)
GeoGauge
36 inches wide, 72 inches
long and 36 inches deep
(Clay and Florolite)
PFWD
36 inches wide, 72 inches
long and 36 inches deep
(Clay and Florolite)
GeoGauge
4 feet x 4 feet x 4 feet box
(Medium sand, crushed
lime rock and mixture of
plastic beads with sand)
7.5-8
Nazzal
(December
2002)
10.5 - 11
Nazzal
(December
2002)
5 – 10
Sawangsuriya
et al. (January
2002)
3.4.3 Quality Control
Both the PFWD and GeoGauge were placed at the center of the bins to achieve an axisymmetric loading configuration. Extra care was taken to ensure good contact with the
surface. If the surface was not level, then a thin layer of fines from the geomaterial
tested was sprinkled on the surface. Fleming et al. (2007) indicated that a thin layer of
sand on an unleveled surface improved contact between the bottom of the instrument
and the geomaterial, which in turn improved modulus readings. However, if the sand
layer is too thick, then the readings can be low.
Also, care was taken to ensure that the instruments were not seated on large particles,
which can yield erroneously high moduli. The GeoGauge was run before the PFWD
since the PFWD exerts a larger strain on the material. At each lift and on each day
post-compaction that the GeoGauge or PFWD were used, a minimum of 5 readings
were made. All the raw deflection-time histories from the PFWD were plotted and
204
evaluated for quality. If the number of PFWD readings are less than 5, it implies that
some data were omitted based on the deflection-time histories. Typically at least 5
readings were obtained per lift except for the first two lifts of RAP.
3.4.4 Test Results
The GeoGauge‘s and PFWD‘s default value of Poisson‘s ratio is 0.35. Based on high
quality tests on granular soils reported by Lade (2005), the Poisson‘s ratio ranged from
0.17 to 0.26 with an average value of 0.2. Since RCA and RAP are also granular, a
Poisson‘s ratio of 0.2 was adopted in this study.
3.4.4.1 Elastic Modulus During Compaction
Figures 3-38a and 3-39a plot the moduli versus depth for RAP and RCA, respectively
along with interpreted trendlines. The average moduli and some statistics for RAP and
RCA are summarized in tables 3-7 and 3-8, respectively. It is observed that the scatter
(coefficients of variation) is much larger in the GeoGauge results than the PFWD.
205
(c)
Height (inches)
Figure 3-38 RAP stiffness, dry density and moisture content versus height
206
Figure 3-39 RCA stiffness, dry density and moisture content versus height
207
Table 3-7 RAP stiffness for each lift
PFWD
Lift
1
2
3
4
5
6
Depth (in)
7
12
18
24
30
36
Eavg (ksf)
4073.2
3413.7
2584.7
2082.4
2051.5
2382.6
GG
COV (%)
2.5
0.9
1.43
2.76
1.08
0.72
No. of
Readings
4
3
5
10
7
6
Eavg (ksf)
2039.5
1832.9
1261.0
1585.2
1967.4
1713.3
COV (%)
1.82
2.16
2.98
2.41
3.91
3.27
No. of
Readings
3
4
5
5
5
5
Table 3-8 RCA stiffness for each lift
PFWD
Lift
1
2
3
4
5
6
Depth (in)
6
12.43
18
24.08
30.03
36.3
Eavg (ksf)
2597.7
3389.4
2347.2
2203.0
2307.7
2161.3
GG
COV (%)
1.27
0.92
1.27
3.71
1.55
0.39
No. of
Readings
5
5
5
5
5
4
Eavg (MPa)
1381.5
1783.1
2204.4
1839.0
1871.9
1860.8
COV (%)
4.82
7.03
3.36
3.67
2.88
1.58
No. of
Readings
5
5
5
5
5
5
In general, the stiffness was highest in the lowest lift. Then, it decreased towards a
constant value. Also, the PFWD consistently yielded higher moduli than the GeoGauge.
This is unexpected because the GeoGauge imparts smaller strains than the PFWD and
is expected to yield larger moduli. This trend has also been observed by Abu-Farsakh
et al. (2004) and Alshibli et al. (2005) in cement-stabilized soils. The nature of the
loading (annular versus circular and vibratory versus impact) and the zones of influence
for the two instruments are dissimilar (Table 3-6).
Also, the geomaterial may be
cemented. The result is a trend in a complex problem that is difficult to rationalize and
should make an interesting further study.
In Figure 3-38a, the change in RAP moduli with depth using the PFWD is much more
dramatic than with the GeoGauge.
The GeoGauge moduli seem to be relatively
constant after the first lift while the PFWD moduli became constant only after the third
208
lift. An attempt was made to keep the dry density and water content constant in each lift
(Figures 3-38b, 3-38c, 3-39b and 3-39c) but inevitably, some scatter could not be
avoided. The fact that the GeoGauge stiffness became constant more rapidly than the
PFWD can be explained as follows: the zone of influence of the GeoGauge is smaller
than that for the PFWD (Table 3-6). Hence, the PFWD stiffness is more affected by the
concrete floor in lifts that extend higher than during GeoGauge testing.
In Figure 3-39a, there are two moduli outliers - the GeoGauge modulus in lift one (6inch depth) and the PFWD modulus in lift two (12-inch depth). These outliers cannot be
explained alone by the variation in the dry unit weight and water content. It can only be
theorized that the deviation may be attributed to a seating problem of the instruments.
3.4.4.2 Post Compaction Measurements
Figures 3-40 and 3-41 show the variation of moduli with time for RAP and RCA,
respectively. In Figure 3-40, the modulus of RAP continually increased with time. This
may be because the moisture content of RAP decreased over the duration of the
experiment due to a downward percolation of water as shown in Figure 3-27.
In Figure 3-41, the modulus of RCA increased to a peak at about 20 days and then
decreased. The initial increase is consistent with a reduction in moisture content and
hydration of cement.
It is postulated that the subsequent decrease is caused by
shrinkage cracking, which was also observed by Abu-Farsakh et al. (2004) and Alshibli
et al. (2005) in cement stabilized soils.
Table 3-9 and 3-10 summarize the average post-compaction moduli for the top lift, the
coefficients of variation and the total number of readings. Again, the coefficients of
variation again are much larger with the GeoGauge than with the PFWD.
209
Figure 3-40 RAP elastic modulus versus time
Figure 3-41 RCA elastic modulus versus time
210
Table 3-9 Variation of RAP stiffness with time
PFWD
Days
0
5
11
15
25
43
63
Eavg (ksf)
2382.6
2735.7
3107.6
3745.0
3279.5
4510.8
4589.3
COV (%)
0.72
0.9
0.07
0.89
1.39
1.12
1.36
GG
No. of
Readings
6
4
3
5
3
4
8
Eavg (ksf)
1713.29
1831.92
1995.54
2139.83
2631.38
3005.79
3533.02
COV (%)
3.27
2.09
2.71
2.56
2.1
2.8
1.32
No. of
Readings
5
4
5
5
5
4
4
Table 3-10 Variation of RCA stiffness with time
PFWD
Days
0
5
9
19
37
57
Eavg (ksf)
2161.3
4542.5
6278.6
8763.5
3294.4
4088.3
COV (%)
0.39
0.25
1.24
0.26
2.8
0.67
GG
No. of
Readings
4
5
4
5
5
5
Eavg (ksf)
1860.8
3816.7
3245.6
4114.3
1832.6
1610.2
COV (%)
1.58
3.45
2.16
0.99
2.24
2.09
No. of
Readings
5
5
6
4
5
5
3.4.4.3 Correlation Between PFWD and GeoGauge Stiffness
Figures 3-41 and 3-42 compare the moduli obtained from the PFWD and GeoGauge.
Figure 3-42 RAP PFWD and GeoGauge modulus comparison
211
Figure 3-43 RCA PFWD and GeoGauge modulus comparison
It is evident that there is little correlation between the PFWD and GeoGauge measured
in the six different lifts (R2 = 0.16 and -1.02 for RAP and RCA, respectively). The PFWD
and GeoGauge post-compaction moduli measured at the top lift correlated better with
less scatter (R2 = 0.76 and 0.63 for RAP and RCA, respectively). If the as-compacted
and post-compaction moduli were combined into the same dataset, the R 2 for RAP and
RCA were 0.55 and 0.67, respectively.
3.4.5 Summary and Conclusions
In this section, the objectives were to: (a) measure the PFWD and GeoGauge moduli of
RAP and RCA in each of the six lifts as the material is compacted in 3-foot-diameter
polyethylene bins; (b) assess the variation of the moduli of the top lift over a postcompaction period of two months; and (c) determine if there is a correlation between the
PFWD and GeoGauge moduli of RAP and RCA. The following conclusions are offered:
212
1. The PFWD consistently provided higher moduli than the GeoGauge for RAP and
RCA.
2. The PFWD gave more repeatable moduli than the GeoGauge (PFWD moduli
coefficients of variation were lower). This may be because the quality of the
PFWD results can be assessed using displacement-time histories.
3. It is important to consider the zone of influence when interpreting PFWD and
GeoGauge moduli. That the GeoGauge stiffness became constant more rapidly
than the PFWD is attributable to the influence of the concrete floor extending
further up with the PFWD than with the GeoGauge.
4. With respect to the variation of stiffness with time:
a. The RAP stiffness increased over the 2 month post-compaction period
probably due to a drop in the moisture content as water percolated
downwards with time.
b. The RCA stiffness increased to a peak and subsequently decreased. The
initial increase in stiffness is due to pozzolanic reaction in the RCA. The
subsequent drop in stiffness may be attributed to shrinkage cracks in the
RCA, which has also been observed in other studies on cement-stabilized
soils.
5. There is a stronger correlation between the PFWD and the GeoGauge moduli
after compaction than during compaction.
compacted lifts was non-existent.
213
In general, correlation in the six
3.5 EARTH PRESSURES
3.5.1 Introduction
The lateral earth pressure coefficient, K, relates the horizontal (h‘) and vertical (v‘)
effective stresses as follows:
K
'h
'v
(3.22)
For a normally consolidated material, the at-rest earth pressure coefficient (Ko nc) can be
approximated by the following relationship (Jaky, 1944):
K o nc 1 sin
(3.23)
where is the effective friction angle of the soil. Equation 3.23 is used extensively to
estimate the horizontal stresses in the base, subbase and subgrade when designing
pavements using the MEPDG (ARA, Inc., 2004). However, these pavement layers are
typically proof-rolled in the field. Compaction induces preconsolidation. During primary
unloading, the overconsolidated at-rest earth pressure coefficient (Ko
oc)
can be
approximated as follows (Kulhawy and Mayne, 1990):
K o oc (1 sin )OCRsin
(3.24)
where OCR is the overconsolidation ratio = vm‘/v‘ and vm‘ = preconsolidation stress.
Since OCR is always greater than 1 for overconsolidated geomaterials, Ko oc is always
greater than Ko
nc.
One of the objectives of this experiment was to measure the
compaction-induced lateral earth pressure of RAP and RCA in the bins and to
investigate the effects of compaction on the value of Ko nc.
214
3.5.2 Literature Review
3.5.2.1 Rankine Active and Passive Lateral Earth Pressure Coefficients
Rankine (1857) developed the following expressions for the active (Ka) and passive (Kp)
earth pressure coefficients
Ka
1 sin '
1 sin '
(3.25)
Kp
1 sin '
1 sin '
(3.26)
Rankine‘s equations 3.25 and 3.26 apply when there is no friction between the soil and
wall and when the failure surface is planar (Figure 3-44). However, studies have shown
that the failure surface is typically curved and approaches that of a logspiral. There is
no simple equation for the logspiral active and passive pressure coefficients. They can
be estimated using tables and figures from the geotechnical literature.
Figure 3-44 Planar and logspiral failure surfaces (Clough & Duncan, 1991)
215
3.5.2.2 Stresses in Silos
Retaining wall problems are typically plane strain; i.e.; they are long in the out-of-plane
direction unlike in a bin, where the problem is axi-symmetric. To calculate the vertical
and lateral pressures in the bins, theories for estimating pressures on a silo wall can be
used. Janssen‘s (1895) and Reimbert and Reimbert‘s (1976) theories were developed
for the design of silos to store grains, coals, cement, etc. These theories apply to any
shaped silos and type of ensiled material.
Janssen’s (1895) Theory
Figure 3-45 shows a schematic of the stresses acting on an element of material of
thickness dz in a silo. Let v = vertical stress at depth z and v + dv = vertical stress at
depth z + dz. The lateral stress h = Kv. The shear stress = h = Kv where =
friction coefficient between the wall and the ensiled material.
Figure 3-45 Forces in a silo (Janssen, 1895)
216
Resolving forces in the vertical direction yields:
A( v d v ) K v Pdz Adz A v
(3.27)
where P = silo perimeter and A = silo cross-sectional area. Rearranging yields the
following first order differential equation:
d v
KP
v
dz
A
(3.28)
Solving the differential equation, v and h can be derived as follows:
v
D
1 e
4 K
4 Kz
D
(3.29)
4 Kz
D
h K v
1 e D
4
(3.30)
where D = silo diameter. It can be seen from equations 3.29 and 3.30 that as z →∞, v
→
D
D
and h →
. It should be noted that Janssen‘s theory assumes that the
4 K
4
lateral earth pressure coefficient, K, remains constant throughout the entire depth.
Reimbert and Reimbert’s (1976) Theory
The main difference between Janssen‘s theory and Reimbert and Reimbert‘s (1976)
theory is that Reimbert and Reimbert assumed a curved variation of wall friction with
depth based on stress measurements on silo walls.
v and h for Reimbert and
Reimbert‘s theory are as follows:
1
v z
1 4 Kz
D
(3.31)
217
1
D
h
1
2
4
4 Kz
1
D
(3.32)
It can be seen from Equation 3.31 that as z →∞, v →
D
D
and h →
; i.e.; identical
4 K
4
to Janssen‘s theory. By dividing Equation 3.32 by 3.31, it can be shown that the lateral
earth pressure coefficient, h/v, initially decreases with depth followed by an increase
(Reimbert and Reimbert, 1976). In summary, the Janssen and Reimbert and Reimbert
silo theories yield the same vertical and lateral pressures at large depths.
The
difference between these two theories is in the variation of the stresses at shallow
depths.
3.5.3 Sensors
The bin wall earth pressures were measured using A201 FlexiForce® electrical sensors
manufactured by Tekscan, Inc. The sensor is 0.008 inches thick, 0.55 inches wide and
7.75 inches long. Located at one end, the sensing area is 0.375 inches in diameter.
The other end of the sensor is a 3-pin male connector. The center pin is inactive. The
outer portion of the sensor is made of polyester while the conductive traces are silver.
The sensor is extremely flexible and can conform to many different shaped surfaces,
making them ideal for use on the circular bin walls.
Each sensor is connected to a transmitter. The transmitters send the data to a hub
wirelessly.
The hub is connected to the USB port of a computer.
The Wireless
Economical Load and Force (WELF) software reads the information from each
transmitter and coverts it to a load based on the calibration factor.
218
3.5.3.1 Calibration
Calibration of the sensors was performed prior to the experiments. To calibrate the
sensors, a known weight is placed on the sensing element and the sensor resistance
output is determined and plotted. This is repeated using a number of known weights
over a range that resembles the forces that will be encountered during the experiment.
It is also important to recalibrate the sensors if they are not used for a long period of
time.
3.5.3.2 Set Up
Four sensors were used in each bin (Figure 3-46).
Figure 3-46 Sensor locations
One sensor was placed at the bottom center of the bin to measure the vertical stress.
Three sensors were placed along the wall of the bins (at 0.25, 1.25, and 2.25 feet above
the bottom) to measure the horizontal pressures. The sensors at 1.25 feet in both bins
219
did not work during the experiments despite the fact that extreme care was taken when
compacting adjacent to a sensor.
It was found that the accuracy of the sensor readings stabilized with time. Therefore,
the sensors were left on during the entire compaction phase of the experiment and the
earth pressure is estimated based on the ―long-term‖ sensor readings.
3.5.4 Test Results
3.5.4.1 Dial Gauge Readings
Figure 3-22 shows the RCA bin wall displacements obtained from dial gauge readings.
Dial gauges were placed at one and two feet above the bottom of the bin. Based on the
dial gauge readings and with the aid of the wall movement to height ratios from Clough
and Duncan (1991) to distinguish active from at-rest behavior, it was found that the
movements were small enough that the bin walls can be considered to be in an at-rest
state.
The RAP bin wall dial gauges were inadvertently dislodged during the
experiment. In light of the movements observed in the RCA bin, at-rest conditions were
also assumed for RAP.
3.5.4.2 Interface Friction Angle
The interface friction angle between soil and the cross-linked polyethylene wall, , was
estimated using Koerner‘s (1998) recommended efficiency of 0.56 for high-density
polyethylene (HDPE) geomembrane/concrete sand interface defined as follows:
E
tan
tan
(3.33)
A literature search for the efficiency of CLPE was not successful. Based on measured
friction angles of 50.7° and 42.8° for RCA and RAP (Selvarajah, 2009), the interface
220
friction angles were calculated to be 34.4° and 27.4° corresponding to of 0.68 and
0.52 for RCA and RAP, respectively.
3.5.4.3 Depth vs. Vertical Stress
Figures 3-47 and 3-48 present v in the RAP and RCA bins, respectively. The lines
represent v calculated assuming free-field conditions (v = z), Reimbert and
Reimbert‘s and Janssen‘s theories. The measured v at a depth of 3 feet is also plotted
for comparison. This plot shows that v from silo theories are less than the free-field
values because wall friction reduces v. The measured v in both the RAP and RCA
were close to the free-field v, but larger than v calculated using Janssen‘s and
Reimbert and Reimbert‘s theories. This suggests that the value of is much smaller
than estimated and that silo theories do not have to be considered in this experiment.
Figure 3-47 Vertical stress versus depth for RAP
221
Figure 3-48 Vertical stress versus depth for RCA
3.5.4.4 Depth vs. Lateral Pressure
Figures 3-49 and 3-50 present h in the RAP and RCA bins, respectively. The graph
includes the upper passive and lower active limits of horizontal stress calculated using
logspiral lateral pressure coefficients. These two lines represent the extreme limits
between which, the data must lie. Also shown are the free-field at-rest, Janssen‘s and
Reimbert and Reimbert‘s h. These three curves were determined assuming K = Ko nc
(Jaky, 1944).
The measured h at depths of 0.75 and 2.75 feet are also shown.
Measured values of h are much higher than the theoretical ones.
This can be
attributed to the effects of compaction as explained in Section 2.11.1.1.1. For RAP, the
calculated compaction-induced Ko (= h measured/v free field) varied from about 2.6 (at 0.75
ft depth) to 0.53 (at 2.75 ft depth), which are about 8.2 and 1.7 times the normally
consolidated Ko value, while this ratio is about 0.8 for RCA at both depths, which is
about 3.5 times the normally consolidated Ko value.
222
Figure 3-49 Depth versus lateral stress for RAP
Figure 3-50 Depth versus lateral stress for RCA
223
It can be seen that the free-field at-rest stresses plot between the Reimbert and
Reimbert‘s and Janssen‘s lateral pressures. Reimbert and Reimbert‘s h is higher than
the free field, while Janssen‘s h is lower than the free field.
3.5.5 Summary and Conclusions
The objectives of this section were to compare the measured earth pressures with
theory so as to determine the impact of compaction on the lateral stresses.
The
following summary and conclusions are offered:
1. The measured v at the bottom of the bin was similar to the free-field but higher
than v calculated using silo theories. Based on this observation, the effects of
wall friction is insignificant in these bins.
2. Dial gauge readings from Figure 3.22 show that the wall movements are
negligible and that at-rest conditions prevail.
3. Compaction significantly increased the locked-in lateral stress from its normally
consolidated at-rest value as the measured lateral stresses are much higher than
theoretical values calculated assuming at-rest conditions.
calculated compaction-induced (Ko = h measured/v
free field)
For RAP, the
varied from about 2.6
(at 0.75 ft depth) to 0.53 (at 2.75 ft depth), which are about 8.2 and 1.7 times the
normally consolidated Ko value, while this ratio is about 0.8 for RCA, which is
about 3.5 times the normally consolidated Ko value.
224
CHAPTER 4 POTENTIAL FOR TUFA PRECIPITATION WITH CRUSHED CONCRETE
CONTAINING
COARSE
BASALTIC
AND
FINE
CORALLINE
SAND
AGGREGATES
4.1 INTRODUCTION
Reuse of crushed recycled concrete aggregate (RCA), derived from demolition of
existing Portland Cement Concrete (PCC) structures and pavements, as road base and
subbase course and as backfill has significant environmental and economical benefits.
They include reduction in waste disposal in landfills and preservation of natural
resources by reduced mining of virgin aggregate, thereby leading to more sustainable
construction practices. Despite its advantages, RCA performance-related issues that
need to be addressed include asbestos and lead paint contamination, high pH, sulfate
attack, alkali-silica reaction, alkali-carbonate reaction and formation of tufa, which is a
calcite or calcium carbonate (CaCO3) precipitate that has the ability to clog drainage
systems and filter fabrics.
The focus of this study is on tufa formation.
Clogged
systems can lead to water retention and generation of large excess pore pressures
especially when used below a roadway. According to Gupta and Dollimore (2002), tufa
formation ―is due to excess dissolution of calcium ions ……………. caused by
absorption of carbon dioxide into the aqueous solution.‖
Based on a survey of the various state departments of transportation (Gupta and
Kneller, 1993), tufa-related problems of varying degrees have been reported in Iowa,
Kansas, Maryland, Minnesota, Ohio, Pennsylvania and West Virginia. Consequently,
225
many of these states limit the percent of RCA in unbound pavement layers.
Interestingly, not all states report such problems.
Use of RCA in highway projects as a base/subbase in the continental USA and abroad
has been gaining popularity. The state of Hawaii Department of Transportation (HDOT)
is considering utilizing RCA in its projects. The RCA coarse aggregate in Hawaii is
basalt while the fine aggregate is commonly coralline sand. This study investigates
whether tufa will precipitate when RCA containing such an aggregate mixture reacts
with carbonic acid in rainwater in an accelerated testing environment.
4.2 LITERATURE REVIEW
Based on laboratory and field studies, Snyder and Bruinsma (1996) agreed with
Michigan DOT‘s suggestion that calcium ion concentration tests can be used to quantify
the precipitate potential of RCA, but no benchmark criterion was available then.
Bruinsma et al. (1998) indicated that the amount of calcite precipitate is influenced by
(a) the contact time of the drainage water with the aggregate; and (b) the aggregate
surface area; i.e., aggregates with more fines, which have a larger surface area, have a
higher precipitation potential.
Gupta and Kneller (1993), Dollimore et al. (2000) and Gupta and Dollimore (2002)
applied thermal analysis and X-ray diffraction (XRD) test to establish the portlandite
[Ca(OH)2], dolomite [CaMg(CO3)2] and calcite [CaCO3] content in RCA from Ohio.
Dollimore et al. (2000) concluded that the calcium content from the carbonate
components of the aggregate affects calcite deposition while the small quantities of
226
portlandite from the cement paste ―would not seem to make this material a significant
factor in calcite precipitation.‖
Gupta and Dollimore (2002) asserted that ―in general, good quality cement does not
produce tufa.‖
Rather, tufa may be produced from ―processed fine aggregates of
dolomitic or calcitic origins‖ as the RCA tested from Ohio consisted mostly of dolomite
and calcite. Based on leaching tests of RCA in acidic water (CO2 in water), their studies
evaluated the leachate concentration of magnesium and calcium ions using Inductive
Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). Their studies confirmed
previous work (e.g., see Drever, 1988) which indicated that in the dolomite/calcite
equilibrium,
CaMg(CO3)2 + Ca2+ = 2 CaCO3 + Mg2+
A ratio of Mg2+/ Ca2+ > 0.6 will favor tufa (CaCO3) precipitation in the presence of
carbonate in rainwater. Based on this, they recommended that leachates should have a
Mg2+/Ca2+ ratio of less than 0.6 for RCA to be used as base/subbase course. This last
recommendation pertains to dolomitic-based RCA.
A literature review has not revealed any studies on the tufa precipitate potential of RCA
containing coarse basaltic and fine coralline sand aggregates. Basalt typically has a
composition by weight of 45 - 55% of SiO2, 2 – 6% of total alkalis (Na2O, K2O), 0.5 – 2%
of TiO2, 5 - 14% of FeO, 5 – 12% of MgO, ~10% of CaO and 13% or more of Al2O3.
Pyroxene, olivine and plagioclase are the most common minerals. The fine coralline
sand aggregate is predominantly calcium carbonate.
227
4.3 CHEMISTRY OF TUFA
Tufa exists in nature from the precipitation of calcium ions and dissolved CO 2 in natural
waters.
Ca2+(aq) + CO32- (aq) ↔ CaCO3(↓)
The source of the carbonate ions is typically CO2 in the air, which dissolves in rain or
natural water to form carbonic acid, H2CO3.
CO2 + H2O ↔ H2CO3
Carbonic acid disassociates to form mostly bicarbonate ions:
H2CO3 ↔ H+ + HCO3Bicarbonate ions increase the solubility of the calcium ions (Gupta and Dollimore,
2002).
Possible sources of Ca2+ in the RCA from Hawaii include Portland cement, basalt
and/or coralline sand. Cement is manufactured by crushing clay and limestone together
and then firing it in a kiln. The end product consists mostly of calcium silicates and
aluminates.
Calcium hydroxide or portlandite is one of the bi-products of cement
hydration. Portlandite is not very soluble in water. In fact, its solubility decreases with
increasing alkalinity. Since concrete is naturally alkaline, it is unlikely that the calcium
ions in tufa will come from cement. Instead, Gupta and Dollimore (2002) suggest that
the calcium ions are derived primarily from the aggregate, which is predominantly
dolomite in their state of Ohio.
228
For tufa to precipitate, one of the following three conditions must exist (Gupta and
Dollimore, 2002): (a) change in pH leading to a change in solubility; (b) evaporation; (c)
change in temperature to cause freezing and thawing.
4.4 CHARACTERIZATION OF THE AS-RECEIVED RCA
Samples of RCA were obtained from a paving contractor on the island of Oahu, Hawaii.
A petrograhic description of the RCA is made based on visual observation of thin
sections. X-ray fluorescence (XRF) tests were conducted on the as-received RCA to
determine its elemental composition.
4.4.1 Petrographic Description of the RCA
Standard-size (25 x 40 mm) rectangular, polished petrographic thin sections (thickness
30 microns) of the RCA samples were made to enable a petrographic description and
in-situ micro-analytical analysis to be made. The RCA is composed of angular basalt
fragments, 5-15 mm in size, embedded in a matrix of predominantly fine (0.1-0.5 mm)
coralline sand and cement. Visually estimated proportions are 60-70 modal percent
basalt, 10-15 percent sand and 10-15 percent cement.
The angular basaltic fragments are compositionally and texturally typical of Hawaiian
lava flows and feeder dikes, as quarried in a few locations on the island of Oahu. Most
fragments are olivine-phyric basalts with a very fine-grained to microcrystalline massive
groundmass consisting of plagioclase microphenocrysts, opaque titanomagnetite and
less abundant calcic clinopyroxenes. Less common are feeder-dike derived, slightly
coarser grained diabase fragments, which contain similar mineralogy but with a coarser
groundmass consisting of euhedral magnetites and plagioclase laths with a very strong
229
lattice preferred orientation.
Despite more than a million years of exposure to the
tropical climate, they have undergone little to moderate degrees of low-temperature
hydrous alteration, preserving most phenocryst and groundmass minerals.
The fine aggregate sand is predominantly composed of well-rounded, biogenic micritic
carbonate fragments such as fragments of corals and bivalves, with some subrounded
basalt fragments, typical of beach deposits. The cementitious matrix was not studied
petrographically.
4.4.2 Elemental Composition of the RCA
The basic principle of the XRF is to bombard the sample with X-ray.
The sample
fluoresces with X-ray peaks at characteristic energies depending on its elemental
composition. Major elements are analyzed by the methods outlined in Norrish and
Chappell (1977).
XRF was performed using a Siemens SRS-303AS wavelength dispersive X-ray
spectrometer, having a Rh X-ray source at 60 kV and 45 mA. Powdered RCA sample is
mixed with lithium metaborate, ignited at 900°C and cast into a glass disk.
Major
element data are reported as weight of oxides in percent. Results of duplicate XRF
tests conducted on the as-received RCA are summarized in Table 4-1. Compared with
average compositional values for basalt published by Blyth and de Freitas (1984), the
RCA contains significantly more CaO. According to Marske et al. (2008), basalt from
the Kilauea eruption on the Island of Hawaii has around 10 - 12% CaO. Slight variation
in the CaO content was observed in the older volcanoes; e.g. the basalt from a quarry in
Makakilo on the island of Oahu, was found to contain 8.4% CaO on average based on
230
XRF testing (sample size = 36). This implies that 12 – 16% of the calcium is from the
cement and/or fine aggregate (coralline sand which is predominantly CaCO 3) used in
the manufacture of concrete in Hawaii.
Table 4-1 X-ray fluorescence test results on the as-received RCA showing the major
elements reported in terms of weight of oxides in percent
Composition (%)
Al2O3
Fe2O3
11.6
10.8
MgO
6.48
Na2O
1.78
8.4
13.6
14.1
8.10
3.10
50.7
10.7
13.3
12.2
7.60
2.20
49.1
9.0
15.7
5.4
6.20
3.10
Material
RCA Sample
Makakilo (Oahu) Basalt
Measured
Published Average for
Basalt from the Kilauea
eruption on the Island of
Hawaii (Marske et al.,
Published Average for
Basalt (Blyth and de
Freitas, 1984)
SiO2
39.3
CaO
24.1
47.8
4.5 LEACHING EXPERIMENT
Leaching tests were performed by soaking two sets of the RCA aggregate in rain water
for over three months. In the first set, CO2 gas was bubbled through the rain water and
aggregate for 95 days in an attempt to facilitate the formation of tufa on an accelerated
basis. Serving as a control, the second set was identical to the first except no CO 2 was
bubbled through. Rain water rather than distilled water was used to simulate as closely
as possible the actual environment in the pavement base and/or subbase course.
The aggregate was housed in a soil triaxial test chamber having an acrylic cylindrical
wall (Figure 4-1). A geotextile was placed at the bottom of the aggregate to prevent any
tufa and fines from draining out when periodically collecting the rainwater leachate for
testing. Five kilograms of aggregate was used in each test chamber and the aggregate
compositions and gradations were varied as summarized in Table 4-2.
231
Figure 4-1 Test setup for bubbling CO2 through RCA soaked in rain water. CO2 is fed
through the bottom of each test chamber. It then bubbles up through the aggregate
solution and exits at the top of the chamber into a hose that feeds into the large plastic
container filled with water
232
Table 4-2 Aggregate used in leaching tests and test objectives
Sample
Aggregate
#
1
100% virgin basaltic aggregate
2
50% RCA:50% VA
3
4
100% RCA
100% RCA
5
100% RCA
6
90% RCA and 10% fly ash
Gradation
HDOT subbase
HDOT subbase
Test Objective
Tests 1, 2 and 3 – to study the
effect of percent RCA on tufa
formation
HDOT subbase
Coarser than subbase Tests 3, 4 and 5 – to study the
effects of gradation on tufa
Finer than subbase
formation
Tests 3 and 6 – To study the
HDOT subbase
effects of fly ash on mitigating tufa
Chambers 1, 2 and 3 contained aggregate meeting HDOT‘s gradation requirement for
subbase (Figure 4-2) but the percent ratio of virgin basaltic aggregate/RCA was varied
from 100/0 to 50/50 to 0/100. Chambers 4 and 5 contained 100% RCA, the latter and
former being coarser and finer than HDOT‘s subbase gradation (Figure 4-2). Chambers
3, 4 and 5 allow the effects of gradation on tufa formation to be studied. Chamber 6 is
similar to Chamber 3 except 10% flyash was added to evaluate the effectiveness of fly
Percent Passing (%)
ash in mitigating tufa formation as suggested by Gupta and Kneller (1993).
100%
Subbase
80%
Finer than subbase
Coarser than subbase
60%
40%
20%
0%
0.01
0.1
1
Sieve Size (mm)
10
100
Figure 4-2 State of Hawaii Department of Transportation‘s subbase gradation along with
the gradations finer and coarser than the subbase gradation used in the leaching
experiments
A total of 21 23-kg-tanks of CO2 were used over the 95-day test period.
233
4.6 DISCUSSION OF TEST RESULTS
Both sets of rainwater leachate, with and without CO2 bubbling, were subjected to pH
and ICP-AES testing.
4.6.1 pH of the Leachate
Over the 95-day test duration, pH of the leachate was measured using a Milwaukee
pH600 pH meter with a resolution of 0.1. On the day of each measurement, the pH
meter was attuned using a calibration solution (PINPOINT TM) at a pH of 7. pH values
are summarized in figures 4-3a and 4-3b for the leachate with and without CO2
bubbling, respectively. In Figure 4-3a, the last two readings for Chamber 5 (100% RCA
finer than subbase) and the last reading for Chamber 6 (90% RCA with 10% fly ash)
were not obtained because the leachate was depleted. The aggregate in these two
chambers are finer and have a higher surface area resulting in a greater rate of reaction
and faster depletion of the leachate. Evaporation and leakage also played a part but
the rates should be fairly similar among the various test chambers. Additional rain
water was not supplemented during the tests.
Prior to mixing with aggregate, the pH of the rain water alone was 7.6. Immediately
after mixing with RCA but prior to CO2 bubbling, the pH increased to between 11.4 and
12.3 (time = 0 days – off the scale in Figure 4-3a) except for 100% basalt, where the pH
was 7.7. One day after CO2 was introduced, the pH dropped and eventually stabilized
at about 6.2 to 6.4 (for the 100% basalt, the pH varied between 5.8 and 6.0).
234
For the aggregate without CO2 bubbling, the pH dropped slightly from their initial values.
However, the solution remained highly basic (pH between 11 and 12). pH values for the
100% basalt sample ranged from 7.5 to 8.2.
7
100% basalt - subbase gradation
50% basalt/50% RCA - subbase gradation
100% RCA - subbase gradation
100% RCA - coarser than subbase
100% RCA - finer than subbase
90%RCA/10% flyash
6.8
6.6
pH
6.4
6.2
6
5.8
5.6
5.4
0
10
20
30
40
50
60
Time (days)
(a)
235
70
80
90
100
13
12
pH
11
10
100% basalt - subbase gradation
50% basalt/50% RCA - subbase gradation
100% RCA - subbase gradation
100% RCA - coarser than subbase
100% RCA - finer than subbase
90%RCA/10% flyash
9
8
7
0
10
20
30
40
50
60
70
80
90
Time (days)
(b)
Figure 4-3 pH of leachate (a) with and (b) without CO2 bubbling versus time
4.6.2 ICP-AES Tests on Leachate
ICP-AES tests were conducted throughout the course of the experiment to measure the
Ca2+ and Mg2+ ions in the RCA leachate. Using a Vista-MPX CCD Simultaneous ICPOES manufactured by Varian, Inc., an aerosol of the leachate is first humidified with
argon gas and atomized with a plasma torch. This excites the electrons present in the
leachate, which then emits light energy at specific wavelengths that are unique
depending on the elemental composition. A spectrometer measures the intensity of the
light energy, which can then be correlated to the concentration of that element.
Figures 4-4 and 4-5 show the variation of Ca2+ and Mg2+ concentrations with time in the
leachate with and without CO2 bubbling, respectively. From these figures, the following
are observed:
236
100
1) The Ca2+ and Mg2+ with CO2 bubbling are significantly higher than those without
bubbling.
2) With CO2, the Ca2+ and Mg2+ concentrations increased with increasing RCA content
(Figs. 4-4a-c).
237
600
Concentration (ppm)
Concentration (ppm)
700
Ca²+
Mg²+
500
400
300
200
100
0
20
40
60
Time (days)
(a)
80
500
400
300
200
100
100
700
Concentration (ppm)
Concentration (ppm)
600
0
0
600
500
400
300
200
100
0
0
20
40
60
Time (days)
(b)
80
100
0
20
40
60
Time (days)
(d)
80
100
0
20
40
60
Time (days)
(f)
80
100
700
600
500
400
300
200
100
0
0
20
40
60
Time (days)
(c)
80
100
700
Concentration (ppm)
Concentration (ppm)
700
600
500
400
300
200
100
0
700
600
500
400
300
200
100
0
0
20
40
60
Time (days)
(e)
80
100
Figure 4-4 Ca2+ and Mg2+ ion concentration in the leachate with CO2 bubbled through
versus time. (a) 100% virgin basaltic aggregate – subbase gradation; (b) 50% RCA and
50% virgin basaltic aggregate – subbase gradation; (c) 100% RCA - subbase gradation;
(d) 100% RCA – coarser than subbase gradation; (e) 100% RCA – finer than subbase
gradation and (f) 90% RCA (subbase gradation) and 10% flyash
238
Concentration (ppm)
Concentration (ppm)
500
Ca²+
Mg²+
400
300
200
100
0
20
40
60
Time (days)
(a)
80
300
200
100
100
500
Concentration (ppm)
Concentration (ppm)
400
0
0
400
300
200
100
0
20
40
60
Time (days)
(b)
80
100
0
20
40
60
Time (days)
(d)
80
100
0
20
40
60
Time (days)
(f)
80
100
500
400
300
200
100
0
0
0
20
40
60
Time (days)
(c)
80
100
500
Concentration (ppm)
Concentration (ppm)
500
400
300
200
100
0
500
400
300
200
100
0
0
20
40
60
Time (days)
(e)
80
100
Figure 4-5 Ca2+ and Mg2+ ion concentration in the leachate without CO2 bubbled
through versus time. (a) 100% virgin basaltic aggregate – subbase gradation; (b) 50%
RCA and 50% virgin basaltic aggregate – subbase gradation; (c) 100% RCA - subbase
gradation; (d) 100% RCA – coarser than subbase gradation; (e) 100% RCA – finer than
subbase gradation and (f) 90% RCA (subbase gradation) and 10% flyash
239
3) With CO2, the Mg2+ concentrations increased with time at a very slow rate.
In
contrast, the Mg2+ ion concentration in similar experiments performed on an RCA
containing a slag and dolomitic aggregate from Ohio increased very rapidly to 620
ppm within 5 days (Figure 4-6 after Gupta and Dollimore, 2002). Since dolomite
(CaMg(CO3)2) contains an abundance of Mg2+ ions and since the solubility of MgCO3
(3.5 x 10-8) is an order of magnitude higher than that of CaCO 3 (3.8 x 10-9), the Mg2+
ions will preferentially remain in solution while the Ca2+ ions will combine with the
CO32- ions to precipitate as tufa (Gupta and Dollimore, 2002). However, XRF tests
indicate that the percent MgO is only about a quarter of CaO in the RCA (Table 4-1).
Concentration (ppm)
700
600
500
400
300
200
Ca²+
100
Mg²+
0
0
1
2
3
4
5
Time (days)
Figure 4-6 Ca2+ and Mg2+ ion concentration in the leachate of a RCA sample from Ohio
containing slag with CO2 bubbled through versus time (after Gupta and Dollimore, 2002)
240
4) With CO2, the Ca2+ ion concentration in the RCA leachate increased initially and then
generally decreased after 53 days. After 95 days, the Ca2+ ion concentration was
still significant (465 ppm in Figures 4-4c and 4-4d) suggesting that the Ca2+ ions
have a tendency to remain in solution rather than precipitating. In contrast, the Ca 2+
ion concentration in similar experiments performed on an RCA containing a slag and
dolomitic aggregate from Ohio dropped to 330 ppm within 5 days (Figure 4-6). The
leachate from this RCA had a Mg2+/Ca2+ ratio of 0.57 suggesting that this RCA had a
marginal potential to precipitate tufa.
The tendency for the Ca2+ and Mg2+ ion
concentrations to equilibrate so quickly after 5 days of CO 2 bubbling, as compared to
the Hawaiian RCA whose curves did not crisscross even after 95 days, suggests that
the basaltic RCA has a lower tendency for tufa precipitation than the dolomitic RCA.
5) Dollimore and Gupta (2002) indicated that for tufa to precipitate, one of the following
conditions must exist: (a) change in pH; (b) evaporation; or (c) freeze/thaw or
temperature change. Evaporation and freezing results in a reduction in water and an
increase in the concentration of the mineral ions, which then leads to precipitation.
In this experiment, CO2 was bubbled till the leachate was almost completely
depleted. This is analogous to complete evaporation whereby the concentration of
mineral ions should have been the highest towards the end to facilitate any tufa
precipitation.
4.6.3 Characterization of the RCA Aggregate before and after Leaching Experiment
Tests were conducted on the RCA before and after CO2 bubbling. They include:
(a) X-ray diffraction (XRD); and
241
(b) Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS)
capability on thin sections of RCA. Prior to the leaching experiment, a piece of
RCA was split into two. One half was used to prepare a thin section immediately,
which represents the aggregate before the leaching experiment. The other half
was placed in Chamber 3. After 3 months of CO2 bubbling, the same piece of
aggregate was removed and another thin section was prepared to represent the
aggregate after the leaching experiment.
4.6.4 XRD Test Results
XRD was performed on pulverized samples of the RCA before and after the leaching
experiment using a Scintag Model PAD V X-ray diffraction machine. The powder was
mounted in a sample holder, which was then placed in a goniometer. A scanning rate
of 1 degree per minute was used. Scan angles ranged from 2 to 90 degrees.
Using a 45kV, 40 mA power supply to heat up a copper filament, X-rays generated were
fed through a beryllium window filter before impacting the sample at an angle. A
detector, chilled using liquid nitrogen, received the X-rays after reflection from the
sample. The results consist of peak intensities for various values of 2 where is the
angle of incidence of the X-ray on the sample. Using Bragg's law, can be related to
the inter-atomic spacing (d) of the crystals that exist in the RCA as follows:
d
n
2 Sin
(4.1)
where = wavelength (1.54054Å for this test) and n is an integer. The peak intensities
are plotted versus 2 for the RCA before and after the experiment in Figure 4-7a and 4242
7b, respectively. It is observed that the ―after‖ XRD test results are almost identical to
those before the experiment.
In both results, the three dominant peaks detected include calcite (CaCO3), augite
(Ca(Fe,Mg)Si2O6) and plagioclase (CaAl2Si2O8). Published inter-atomic spacings (Joint
Committee on Powder Diffraction Standards, 1983) for these minerals are in close
agreement with measured values. For calcite, published and measured values of d are
3.035Å and 3.021Å, respectively, for augite d = 2.999Å and 2.991Å, respectively, and
for plagioclase, d = 3.20Å and 3.196Å, respectively. While augite and plagioclase are
the two more common minerals in basalt, the calcite crystals showed a high intensity,
probably because of the presence of coralline sand (mostly calcite), which is used as
fine aggregate in the RCA. However, the similarity of figures 4-7a and 4-7b plus the fact
that the calcite peak is not overwhelming in the ―after‖ sample suggests that tufa has not
formed in appreciable quantities.
1600
Calcite
d = 3.0213Å
Intensity (counts)
1400
BEFORE
1200
1000
Augite
d = 2.9914Å
Plagioclase
d = 3.1963Å
800
600
400
200
0
0
10
20
30
40
50
2 (°)
(a)
243
60
70
80
90
1600
Intensity (counts)
1400
AFTER
Calcite
d = 3.0214Å
1200
1000
Augite
d = 2.9915Å
Plagioclase
d = 3.1972Å
800
600
400
200
0
0
10
20
30
40
50
60
70
80
90
2 (°)
(b)
Figure 4-7 X-ray diffraction results of pulverized RCA (a) before; and (b) after CO2
bubbling through
Though not among the top few peaks, olivine [(Fe,Mg)2SiO4] was also detected (d =
2.81Å) among the top 20 peaks of the XRD. Olivine was petrographically observed in
thin sections of large coarse aggregate pieces. XRD was performed on pulverized
concrete.
Since it was easier to crush cement and fine aggregate rather than the
coarse aggregate, this may explain why olivine was less prominent in the XRD.
4.6.5 SEM with EDS Test Results
Thin sections of RCA before and after CO2 bubbling were observed using SEM with
EDS capability. Magnified images of the thin sections were captured using a JEOL
JXA-8500F SEM by bombarding the samples with high energy electrons. The electron
beam diameter is smaller than 1 micron with an acceleration potential of 15 keV and a
spectrum current of 15 nanoamps.
The electrons interact with the nuclei of the
244
elements generating secondary electrons (SE), backscatter electrons (BSE) and X-rays.
The BSE are used to provide an enlarged image of the sample; e.g., a large deflection
with little energy transfer is characteristic of a nucleus having a large mass and vice
versa.
The SEM images before and after the leaching experiment are shown in figures 4-8a
and 4-9a, respectively.
Images around a void were selected because should any
reaction occur, it would most likely be on the periphery rather than in the interior of the
sample. It is consistently observed that the perimeter of the void of the ―before‖ sample
is smooth and regular while that of the ―after‖ sample appears rough and jagged. This
suggests that some chemical reaction has occurred in the sample periphery. However,
the quantity of the reaction product or precipitation in the void periphery during the
course of the leaching experiment is insignificant considering the scale as shown in the
figures.
245
(a)
(b)
Figure 4-8 (a) SEM image of an interior void in RCA sample and (b) EDS test results
for RCA before CO2 bubbling
246
(a)
(b)
Figure 4-9 (a) SEM image of an interior void in RCA sample and (b) EDS test results
for RCA after CO2 bubbling
247
The EDS results, before and after CO2 bubbling, are shown in Figures 4-8b and 4-9b,
respectively. The principles of the EDS are similar to XRF. The elements detected in
the concrete portion of the ―before‖ sample (Figure 4-8b) consist of elements typically
found in concrete such as Ca, Al, Si and O, consistent with the calcium silicates and
aluminates in cement.
The elements in the basalt portion are not shown for brevity.
The elements detected near the perimeter of the void in the ―after‖ sample (Figure 49b), however, consist primarily of Ca and O with little Si and no Al. Carbon is used as a
backing during the EDS and therefore it will show up regardless of whether any carbon
is present chemically. Thus, it is possible that the reaction product formed in the void is
calcium carbonate or tufa. Since only trace amounts were detected by the SEM, it
could not be practically sampled and analyzed using XRD for further confirmation.
4.6.6 Sample Observation after Leaching Experiment
After 95 days of CO2 bubbling, the RCA was visually examined for evidence of tufa
deposits.
Figure 4-10 shows that the aggregate and the filter fabric placed at the
bottom were completely free of any visible tufa precipitate for the 100% RCA with a
subbase gradation. The same is true for all the other chambers. However, in test
chambers 3 and 5, very small quantities of a thin, non-continuous white film were
observed on the walls. At most, about 1 gram of this film could be collected for further
testing as follows:
248
Figure 4-10 100% RCA (subbase gradation) or Sample 3 after 95 days of CO2 bubbling
showing no appreciable tufa precipitate
1) The film was dried at a temperature of 60ºC for three days.
2) After cooling, sub-samples were weighed and placed in Teflon CEM microwave
digestion containers. Weights varied, from 0.013 grams to 0.103 grams,
depending on the amount of original sample available.
3) 3.0 ml and 1.0 ml of concentrated nitric (HNO3) and hydrochloric (HCl) acids,
respectively, were added to each sample. The reaction vessels were sealed and
allowed to sit for 1.5 hours.
4) 2.0 ml of concentrated hydrofluoric acid (HF) was then added to each sample
and the vessels re-sealed. The samples were then heated in a CEM microwave
249
oven using 50 percent power for 45 minutes to 80 psi and 60 percent power for
30 minutes to 110 psi.
5) Samples were allowed to cool for 3 hours. 10 ml of 0.5-N-boric acid was added
to each sample, which was then allowed to sit overnight.
6) Samples were transferred to clean plastic bottles, rinsed with 18 mega ohm
water, weighed and then analyzed using a Varian Vista MPX ICP-OES.
Results of the test on these precipitates are summarized in Table 4-3. Calcium was by
far the most dominant element detected indicating that the thin film may possibly be
tufa. Other elements were also detected therefore, indicating that some of the film may
also contain a silicate of iron, magnesium and aluminum also. Another observation of
interest is that the concentrations of all the precipitate ions from Chamber 5 (finer RCA
gradation) are higher than from Chamber 3.
increased reaction product.
Thus, a finer gradation does lead to
Again, there were insufficient quantities of the film to
perform an XRD.
Table 4-3 Summary of ICP-AES results on the film collected from the walls of two test
chambers
Sample No.
3
5
Ca
mg/gm
116.26
133.69
Mg
mg/gm
6.51
19.84
Al
mg/gm
15.66
38.92
Fe
mg/gm
17.06
53.51
Na
mg/gm
6.13
9.75
Sr
mg/gm
1.52
0.71
Zn
mg/gm
0.095
0.13
4.7 SUMMARY AND CONCLUSIONS
To examine the tufa precipitation potential of a Hawaiian RCA, two sets of aggregate
were soaked in rain water for approximately 3 months. In one set of samples, CO 2 was
continuously bubbled through while no bubbling was performed on the other set. Tests
250
were conducted on the rainwater over time and on the aggregate before and after CO2
bubbling. The following summary and conclusions are offered:
(1) pH of the rainwater in RCA samples was initially very basic (~12) prior to CO 2
bubbling. Subsequently, the pH dropped to about 6.3 when carbonic acid formed
after CO2 bubbling. pH of the rainwater in RCA samples without CO2 bubbling
remained basic (between 11 and 12).
(2) ICP-AES tests on rain water with CO2 bubbling through the Hawaiian RCA
indicate that the Ca2+ ions have a tendency to remain in solution rather than
precipitating as compared to similar experiments conducted using dolomitebased RCA by Gupta and Dollimore (2002).
Since dolomite contains an
abundance of Mg2+ ions and since the solubility of MgCO3 is an order of
magnitude higher than that of CaCO3, the Mg2+ ions will preferentially remain in
solution while the Ca2+ ions will combine with the CO32- ions to precipitate as tufa.
XRF tests indicate that the Hawaiian RCA contains very little Mg 2+ ions. The
most abundant positively charged metallic ion is Ca 2+, which is at least twice any
other positively charged metallic ion present.
(3) XRD tests were performed on pulverized RCA before and after 3 months of CO 2
bubbling.
The XRD results for the ―before‖ and ―after‖ samples are almost
identical, suggesting that any changes in the RCA as a result of CO2 bubbling
are minimal.
(4) SEM with EDS tests were performed on thin sections of RCA before and after 3
months of CO2 bubbling.
Magnified images of the perimeter of voids in the
251
―before‖ sample is consistently smooth and regular while that of the ―after‖
sample appears more rough and jagged. This suggests that some precipitation
has occurred. However, the quantity of precipitation observed is insignificant.
(5) EDS tests on the precipitate near the void perimeter indicate the presence of Ca
and O with trace amounts of Si. Since carbon is used as a conductive coating, it
was also detected. The carbon quantity was significant enough to suggest that
the reaction product formed in the void is tufa.
However, the quantity is
insignificant for it to pose any concerns for drainage.
(6) ICP-AES tests on about 1 gram of the thin, white film found in test chambers 3
and 5 indicate that it may be tufa with some silicates of iron, magnesium and
aluminum also present.
(7) In conclusion, tufa may potentially form with Hawaiian RCA. However, based on
the quantities observed in the experiments of RCA subjected to extreme CO 2
exposure, the evidence suggests that tufa quantities would be insignificant to
cause any drainage problems.
252
CHAPTER 5 FORENSIC INVESTIGATION OF A DISTRESSED PAVEMENT
SUPPORTED ON A BASE COURSE CONTAINING RECYCLED CONCRETE
AGGREGATE
5.1 INTRODUCTION
Two billion tons of aggregate are being consumed each year in the United States and
this number is continually growing (Gonzalez and Moo-Young, 2004). The impetus and
pressure for pavement and geotechnical engineers to incorporate sustainability in
engineering projects has led to a rise in the reuse of materials such as recycled
concrete aggregate (RCA) as fill and in pavement sub-layers. Using RCA is beneficial
from three perspectives as follows:
Engineering
1. Rubblization of existing concrete pavements removes cracked and aged pavement
surface, improves pavement smoothness, and maintains curb height, drainage inlets
and bridge clearances.
2. Crushed RCA have fractured angular surfaces, which provides greater internal
friction if used as a fill compared to more rounded natural aggregate obtained from
stream and river beds.
3. Crushing concrete exposes unhydrated cement.
If used in pavement unbound
layers, exposure to water can lead to rehydration and a subsequent strength
increase.
Environmental
1. Conservation of landfill space.
253
2. Preservation of natural aggregate resources.
3. Conservation of energy by eliminating or reducing haul distances of RCA to the
landfill and of new aggregate from the quarry.
Economical
1. Reduced transportation and material cost compared to virgin aggregate.
2. Reduced haulage also implies reduced traffic and less wear and tear on existing
roads along the haul routes.
On the flip side, the absence of quality control can lead to poor performance and
premature deterioration that are costly to repair but more importantly, could slow down
market acceptance of this useful recycled material.
This case study provides an
example where early deterioration of a pavement supported on a base course
containing RCA has resulted in reservations on its use in the state of Hawaii. The
cause of the distress was not trivial and is meticulously investigated herein. The results
hint towards contamination of RCA as the probable cause of the deterioration.
5.2 PROJECT DESCRIPTION AND OBJECTIVES
The distress of a 51-mm-thick asphalt concrete (AC) pavement supported on a 152mm-thick base course containing 50% basalt, 25% reclaimed asphalt pavement (RAP)
and 25% RCA, overlying a 2-m-thick coralline sand layer was investigated. Used as a
parking lot on the island of Oahu, Hawaii, the pavement experienced over 30 eruptions
greater than 25 mm high and 127 mm in diameter (Figures 5.1a and b) within one year
after completion of construction and over 100 eruptions after two years. The parcel to
the north is approximately 2 m higher in elevation. Therefore, drainage generally flows
in a southerly direction through the site.
254
(a)
(c)
(b)
(d)
Figure 5.1 (a) and (b) Pavement eruptions; (c) and (d) White reaction product found in the base course
255
To investigate the distress, the pavement was saw cut around one of these eruptions
and the base course was manually excavated. A white substance with occasional blue
tinges was observed in significant quantities directly below the eruption (Figures 5.1c
and d). It was postulated that this substance was related to the pavement eruptions,
and was sampled for further testing and evaluation.
The objectives of this study are to: (1) chemically identify the reaction product; (2)
determine the cause of this distress based on the chemistry of the reaction product; (3)
perform experiments in the laboratory to replicate the reaction; (4) estimate the swell
pressure that can arise as a result of this reaction; and (5) numerically simulate the
heave to see if it corroborates the field observations.
5.3 BACKGROUND
There have been two other known pavements in Hawaii that suffered a similar distress.
The common denominator in these three pavements is that the base courses contained
RCA from a mixture of sources such as building and pavement demolition and returned
ready mix concrete. While there are many advantages of using RCA in a base course
as described above, there are also some known potential drawbacks. They include:
a.
Alkali silica reaction (ASR);
b.
Alkali carbonate reaction (ACR);
c.
Sulfate attack;
d.
Tufa formation;
e.
Corrosion of aluminum pipes that are in close proximity;
f.
High pH;
g.
Lead paint contamination;
256
h.
Asbestos contamination;
i.
Decrease in permeability with time as more cementation occurs; and
j.
High water absorption which may yield unusually high optimum moisture
contents.
The first five drawbacks can form reaction products that have the potential to cause
distress in pavements particularly the more flexible AC variety. Table 5.1 summarizes
the nature of these reactions along with their expected products.
In short, if the
concrete source from which RCA was obtained had ASR or ACR, these problems can
continue if the silicate or dolomitic rocks within the RCA are further exposed to alkalis
(e.g., from brackish water) resulting in additional formation of expansive alkali-silica or
alkali-carbonate products. Sulfate attack is due to exposure of RCA to high sulfate
bearing soils or ground water which results in the formation of expansive ettringite (i.e.,
calcium sulfo-aluminate hydrate) or occasionally thaumasite crystals. Tufa forms from
the precipitation of calcium ions, present in dolomitic or calcitic RCA aggregate, and
dissolved CO2 in natural waters.
Song et al. (2011) showed that tufa formation is
unlikely to be a problem in RCA with a Hawaiian basaltic aggregate. Finally, dissolution
of RCA particles raises the pH of infiltrating water. If aluminum metal is in the vicinity
(e.g., aluminum pipes), it can corrode leading to the formation of aluminum hydroxide,
either in the form of gibbsite or the less stable bayerite, and hydrogen gas; both of
which can produce expansion. Also not to be neglected are drawbacks f through j,
which are more problematic from either a health, environmental or other performance
related viewpoints rather than distress-causing but nonetheless important.
257
Table 5.1 Possible deterioration of RCA and their reaction products.
Distress
Reaction Equation
Reaction Products
Alkali silica reaction
Reaction of silica and alkali
2NaOH + SiO2 + 2H2O → Na2H2SiO4·2H2O
(stoichiometry inexact)
Reaction of dolomite and alkali
CaMg(CO3)2 + 2NaOH → CaCO3 + Na2CO3 + Mg(OH)2
Alkali silica gel
[(Na2O)x(SiO2)y(H2O)z]
Reaction of alumino-silicates and sulfate:
(CaO)3(Al2O3) + 3CaSO4 + 32H2O →
(CaO)3(Al2O3)(SO3)3(H2O)32
Occasionally, formation of thaumasite:
(CaO)(SiO2)(H2O)8+ CaSO4 + CaCO3 + 7H2O →
(CaO)3(SiO2)(CO2) (SO3)(H2O)15 (stoichiometry inexact)
Precipitation of calcium ions and dissolved CO 2 in natural
waters
2+
2Ca (aq) + CO3 (aq) ↔ CaCO3(↓)
Reduction of H2O in basic solution
Al + 3H2O +OH = 3/2H2(g) + Al(OH)4
Precipitation of Al(OH)3 in form of gibbsite or bayerite
crystals
Al(OH)4 = Al(OH)3 + OH
Alkali carbonate
reaction
Sulfate attack
Tufa formation
Corrosion of
aluminum
258
Primary Interatomic Spacing
of the Reaction
Product
(Å)
Amorphous
Reference
Brucite [Mg(OH)2]
Calcite [CaCO3]
2.37
3.04
Ettringite
[3CaO∙Al2O3∙3CaSO4∙32H2O]
9.73
Thaumasite
[CaCO3∙CaSO4∙CaSiO3∙15H2O]
9.66
(Mindess
et al.,
2003)
(Mehta
and
Monteiro,
2006)
Calcite [CaCO3]
3.04
(Song et
al., 2010)
4.37, 4.85
2.22, 4.35, 4.71
(Zhang et
al., 2009)
Gibbsite [Al(OH)3]
Bayerite [Al(OH)3]
(Glasser,
1998)
5.4 EXPERIMENTAL INVESTIGATIONS
To identify the type of distress in the subject pavement, the chemistry of the white
reaction product was investigated using: (1) Scanning Electron Microscopy (SEM)
equipped with an X-ray Energy Dispersive Spectroscopy (EDS) detector; (2) X-ray
Diffraction (XRD); and (3) Raman Spectroscopy.
This is followed by laboratory
simulation of the field reaction. Lastly, a swell pressure test was performed to estimate
the heave pressure that can be exerted under the pavement as a result of such a
reaction.
5.4.1 Identification of the Field Reaction Product
5.4.1.1 SEM with EDS
Magnified images of the white reaction product were captured using a JEOL JXA-8500F
SEM by bombarding the sample with high energy electrons. These electrons interact
with the sample‘s atoms and produce backscattered electrons (BSE), secondary
electrons (SE) and characteristic X-rays. The BSE and SE are collected to produce a
magnified image of the sample.
The energy and wavelength of the X-rays emitted is
specific to the atoms from which they emanate. As such, an EDS X-ray detector is
capable of identifying the chemical composition of the sample both qualitatively (i.e.,
which elements are present) and quantitatively (i.e., how much of each element is
present).
Figure 5.2 shows a 350× magnified BSE image of the reaction product as well as a
typical EDS spectrum. The latter shows two major peaks for aluminum (Al) and oxygen
(O) with traces of silica (Si), copper (Cu), chlorine (Cl), zinc (Zn), sodium (Na), and iron
(Fe). Using the area under each peak, the relative concentration of that element in the
sample can be determined. Table 5.2 shows the elemental composition of both the
259
white and blue tinge portions of the product estimated by averaging the EDS readings
from four different spots on the sample.
It should be pointed out that EDS is not
capable of detecting elements lighter than lithium including hydrogen.
The results
indicate that both samples are mainly composed of aluminum (≥ 50.0%) and oxygen (≥
15.6%) while the blue tinge portion of the product also contained some silica and
copper.
The results show that the pavement distress is likely not caused by sulfate attack (no
sulfur detected), alkali-silica reaction (very little alkali detected), alkali carbonate
reaction (insignificant amount of calcium or no magnesium detected), nor tufa formation
(insignificant amount of calcium detected).
Table 5.2 Average elemental composition of the reaction product from EDS analysis.
Element
Reaction product
White portion of
reaction product
Blue tinge portion of
reaction product
Ca
Si
Al
Fe
Not
detected
0.86
6.15
60.60
0.98
17.07
50.07
1.85
260
S
Na
Atomic %
Not
1.88
detected
0.26
Not
detected
O
Cu
Zn
Cl
22.16
3.41
2.01
2.82
15.62
9.57
4.27
0.45
(a)
(b)
Figure 5.2 SEM with EDS analysis of the white reaction product: (a) SEM image, (b)
EDS output showing the average elemental composition of spot1.
261
5.4.1.2 XRD
The XRD patterns of the reaction product were obtained using a PANalytical X‘pert Pro
MPD diffractometer. The reaction product was mounted in a sample holder, which was
then placed in a goniometer. Using a 45kV, 40 mA power supply, a copper filament
was bombarded by electrons to generate characteristic Cu-Kα X-rays which, after
passing through a beryllium monochromator filter, were radiated towards the sample at
incident angles (θ) ranging from 2.5 to 35 degrees (2θ = 5 to 70 o).
Constructive
interferences at particular values of θ are detected as peak intensities on the XRD
pattern (Figure 5.3). According to Bragg's law, the value corresponding to each peak
is related to the inter-atomic spacing (d) of the crystals forming the sample:
d
n
2Sin
(5.1)
where = wavelength of X-rays (1.54054Å for this test) and n is an integer. Crystalline
compounds have characteristic inter-atomic spacing which can be used for their
identification. For example, a peak at 2=18.3equivalent to d = 4.85Å) can represent
the mineral gibbsite [Al(OH)3]. A collection of the d-spacings for a multitude of different
compounds can be found in the publications of the Joint Committee on Powder
Diffraction, such as standards for minerals (1974) and inorganic compounds (1991).
The XRD patterns of the reaction product (two samples of the white portion of the
reaction product and one sample of the blue tinge portion of the reaction product) are
shown in Figure 5.3 along with the most probable compounds corresponding to each
peak. Major peaks at 2and 20.3o (d = 4.85Å and 4.37 Å) are associated with
gibbsite or Al(OH)3, which is the chemical product of aluminum corrosion.
262
This is
consistent with the EDS results that showed Al and O as the main constituents of the
reaction product (again EDS does not detect H).
Several less pronounced peaks
associated with either gibbsite or bayerite [a meta-stable form of Al(OH)3] were
observed in all three XRD patterns. The peaks at 228.5o, 47.3o and 56.1o d =
1.61Å, 1.05Å and 0.93Å) were also prominent in the blue tinge portion of the reaction
product. These suggest the presence of silicon. Other smaller peaks, associated with
iron (Fe), tenorite (CuO) and magnetite (Fe3O4), were also detected. The combination
of tenorite and silicon is most likely responsible for giving the product its blue hue. More
importantly, the XRD results corroborate the fact that the pavement distress was not
caused by sulfate attack, ACR or tufa formation as the products of these reactions (see
Table 5.1) were not identified in any of the XRD patterns.
263
Gibbsite
d = 4.85Å
Gibbsite
d = 4.37Å
White portion of
reaction product
Blue tinge portion of reaction product
Figure 5.3 XRD test results of the reaction product excavated from the field
264
5.4.1.3 Raman Spectroscopy
Described by Misra et al. (2009), the equipment used to obtain the Raman spectra was
an Invictus 785 nm NIR laser source along with a fiber-coupled micro-Raman RXN
system manufactured by Kaiser Optical Systems, Inc. from Ann Arbor, MI. In this test,
the white reaction product from the field was illuminated by a laser beam. Light from the
sample was then sent through a monochromator. Based on the inelastic or Raman
scattering of the monochromatic light detected, the vibrational modes of various atomic
bonds within the sample is identified which can reveal the sample‘s chemical
composition. Two Raman spectra of the field reaction product are shown in Figure 5.4
denoted as ―Field.‖ According to Ruan et al. (2001), the wavenumbers assigned to the
vibrational modes for bayerite include the following: 1068 for (OH), 545, 569 and 899
for (OH) and 322, 388 and 435 for Al-O. These wavenumbers very closely matched
those from the Raman spectra obtained implying that the field reaction product is
bayerite. The match for gibbsite was non-existent.
The fact that the Raman spectra indicated bayerite while the XRD patterns revealed
gibbsite can be explained as follows.
The Raman spectra were obtained on the
reaction product fresh from the field while the XRD specimen was shipped to
Pennsylvania.
Since bayerite is unstable, it probably spontaneously converted to
gibbsite during transport due to a lack of sample preservation (e.g.; refrigeration).
Nevertheless, these spectra lend credence to the XRD and EDS results, and further
support the aluminum corrosion hypothesis in the distressed pavement.
265
Figure 5.4 Raman spectra for the reaction product from the field and from the laboratory
266
5.4.2 Laboratory Simulation of Field Reaction
There is conclusive evidence that the field reaction product contained Al(OH) 3 as its
main constituent. As shown in Table 5.1, this product can form when aluminum metal
corrodes in an alkaline environment. When RCA particles were placed in 100 ml of
distilled water, the pH of the water was observed to exceed 12.0 within 3 days. That the
ground contours favor drainage through the site with a base course containing RCA
suggests that a highly saturated alkaline environment can be created easily and
naturally. Therefore, what if the source RCA partially contained building demolition
waste such as aluminum metal pieces (from e.g., cladding, posts, flashing, pipes,
window and door frames, etc.)? This possibility offers a plausible explanation for the
pavement distress.
To test this hypothesis, this field reaction was duplicated in the laboratory by preparing
the following samples:
1. 1 gram of aluminum powder or aluminum shavings in 80 grams of NaOH solution
(pH = 12.0); and
2. 1 gram of aluminum powder or aluminum shavings in 28 grams of fresh cement
paste (w/c = 0.4). This was then added to 72 grams of distilled water (measured
pH after 24 hours = 11.8).
In all samples, extensive hydrogen gas was observed minutes after mixing.
The
hydrogen gas was confirmed when a lighted splint extinguished with a pop. In addition,
a white reaction product resembling that in the field was observed within the first 24
hours. It was also evident that this reaction resulted in a net expansion. After three
days, the reaction product was sampled and tested by Raman spectroscopy (Figure 5.4
267
– denoted as ―Laboratory‖) and X-ray diffraction (Figure 5.5). Both tests confirmed the
presence of bayerite [Al(OH)3] as the main reaction product. The Raman spectra for the
laboratory-generated product matched very well with those from the field. One of the
prominent peaks in the XRD pattern (d = 2.22Å) confirmed that the majority of Al(OH) 3
was in the form of bayerite. As expected, the laboratory product did not contain any
silicon or other impurities.
268
Bayerite
d = 4.71Å
Bayerite
d = 4.35Å
Bayerite
d = 2.22Å
Figure 5.5 XRD test results of the reaction product synthesized in the lab.
269
5.4.3 Swell Pressure Test
To estimate the swell pressure exerted on the pavement as a result of this reaction, a
procedure similar to ASTM D4546 Method C was followed. A 20-gram-mixture of dry
aluminum powder and dry cement mixed in a 1:9 ratio by weight was set up in a Geonor
h-200 swelling test apparatus (Figure 5.6a).
The specimen was placed without
compaction in the consolidation cell having a cross-sectional area of 20 cm2.
The
consolidation cell is housed in a 10 kN loading frame with a lever arm ratio of 1:10. A
vertical pressure of 200 tons/m2 was applied on the specimen to simulate the effects of
compaction of the base course and placement and compaction of the overlying AC. The
pressure is applied by turning a hand wheel that operates a worm drive connected to a
screw-thread jack, which in turn is connected to a vertical rod with a pressure gauge.
After the specimen had reached equilibrium, the load was removed completely and
distilled water was poured into the Lucite cylinder to completely submerge the cell and
sample. While maintaining the height of the specimen constant, the swelling pressure
was measured as a function of time. From the results shown in Figure 5.6c, a maximum
swell pressure of 430 kPa was reached after only 15 minutes. Thereafter, the swell
pressure remained constant.
Prior to testing, the compliance of the apparatus was
determined (Figure 5.6b) by measuring the pressure-deflection curve of two wet filter
papers and porous stones without the sample. The compliance curve was necessary to
correct the deflection dial gauge readings when maintaining a constant sample height.
270
(a)
0.18
Deformation (mm)
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0
500
1000
1500
Pressure (kPa)
(b)
271
2000
2500
Pressure [kPa]
500
450
400
350
300
250
200
150
100
50
0
0
50
100
150
Time [min]
200
250
(c)
Figure 5.6 (a) Swelling test apparatus; (b) Apparatus compliance curve without sample;
and (c) Swell pressure as a function of time.
The 430 kPa measured involved the swelling pressure due to a cement/aluminum
mixture rather than RCA with aluminum.
Tests involving finely crushed RCA and
aluminum is expected to produce similar swelling pressures as the crushed RCA or
cement merely provides the alkaline environment. As a result, the swelling pressure of
430 kPa was deemed representative of the field condition and is used in the numerical
analysis described below.
5.5 NUMERICAL ANALYSIS
To numerically model the effects of a 430 kPa swelling pressure on a 50-mm-thick AC
pavement, a 4-m-diameter, axi-symmetric model of the AC, base course and coralline
sand subgrade was created in a finite element software PLAXIS (Brinkgreve, 2002) as
272
shown in Figure 5.7a. Horizontal and total fixities were assigned at the line of symmetry
and the outer periphery of the model, respectively. Although the reaction may have
been triggered by precipitation, the ground water table in general is deeper than the
coralline subgrade soil and therefore, pore water pressures were not generated in the
model. After generating the initial stresses, the 430 kPa heave pressure was applied
over a radius equal to 50 mm from the line of symmetry. The AC was modeled as an
elasto-plastic Mohr-Coulomb material with the properties summarized in Table 5.3 along
with the properties of the base course and coralline sand that are of lesser significance.
Since the problem is one of a pavement heave and to prevent the underlying materials
from having a restraining effect on the AC in finite element modeling, a weak interface
element was specified between the base course and the AC with the interface strength
parameter Rinter = 0.01 where Rinter relates the interface cohesion (ci) and friction angle
(i) to that of the base course as follows:
ci = Rinter cbase course
(5.2)
tani = Rinter tanbase course
where cbase course and base course are the cohesion and friction angle of the base course,
respectively.
Material
Table 5.3 Summary of material properties used in the numerical analysis.
Unit
Weight
3
(kN/m )
23
19
19
At-rest Earth
Pressure Coef.
Ko
Friction
Angle
(°)
1
40
40
40
Cohesion
Dilatancy
Angle
(°)
10
10
10
Young‘s
Modulus
E
(MPa)
2
70 to 600
200
70
Poisson‘s
Ratio
(kPa)
1
Asphalt concrete
0.357
160
0.35
Base course
0.357
0
0.2
Coralline sand
0.357
0
0.2
Notes:
1. Shear strength parameters for AC are for a 5% binder content per Christensen and Bonaquist
(2002).
2. E appropriate for AC with a PG64-16 binder and for the range of temperatures common in Hawaii
per Archilla (2010).
273
The Young‘s modulus, E, of the AC pavement has a significant effect on the deflections.
The moduli of AC can vary significantly with temperature and binder content. For an AC
pavement with a 5% PG64-16 binder content (commonly used in Hawaii) and for the
range of temperatures on Oahu, Hawaii, E can vary from 70 to 600 MPa (Archilla,
2010). A sensitivity analysis of E on the centerline deflection was performed. As shown
in Figure 5.7b, the deflections can vary from 10 to 90 mm for this range of E, which
coincides with the observed field deflections. It can also be seen from the deflected
profile in Figure 5.7a that the pavement separated from the base course as a result of
this uplift.
274
Centerline Deflection (mm)
(a)
100
90
80
70
60
50
40
30
20
10
0
0
200
400
600
800
Young's Modulus of Asphalt Concrete (MPa)
(b)
Figure 5.7 (a) Deformed mesh of the AC pavement when subjected to a swelling
pressure of 430 kPa with an AC Young‘s modulus of 400 MPa and (b) Centerline
deflection versus Young‘s modulus of the AC pavement.
275
5.6 SUMMARY AND CONCLUSIONS
A case study of a pavement containing a significant number of eruptions that were
about 25 mm high and about 127 mm in diameter was forensically investigated. The
distressed AC pavement was constructed on a base course containing RCA.
The
following observations and conclusions are offered:
Directly below each eruption, significant amounts of a white substance were
found within the base course. It was theorized that this white substance was
responsible for the pavement distress and was sampled for testing.
A combination of EDS, XRD and Raman spectroscopy identified that the primary
constituent of the white substance was Al(OH)3 in the form of bayerite, which is
an unstable form of gibbsite. This product can form when impurities such as
pieces of aluminum metal, if present in a base course, corrodes in an alkaline
environment.
An alkaline environment can exist when moisture is present in a base course
containing RCA.
The adjacent ground topography greatly favored drainage
through this site.
Laboratory duplication of the field reaction confirmed the formation of bayerite
when aluminum metal is exposed to an alkaline environment.
A test in a Geonor h-200 apparatus was conducted by exposing aluminum
powder to an alkaline environment. It was found that a maximum swell pressure
of 430 kPa was attained in just 15 minutes.
A numerical analysis was performed by subjecting the pavement to the
measured swell pressure.
For a range of realistic pavement moduli, the
276
calculated deflections are consistent with the observed pavement deflections
thus corroborating the hypothesized cause of this distress.
Considering the extensive costs and effort required to reconstruct this pavement, it is
vital that sufficient quality control practices are adopted to ensure that this case history
is not repeated. When using RCA as a base course, it may be prudent to follow one or
more of the following:
Allow only uncrushed concrete that can be visually inspected for use as RCA;
Allow RCA from a supplier who can guarantee the quality. RCA from unknown
sources should not be accepted unless certified by a qualified engineer/scientist
that it is free of deleterious materials (such as aluminum);
Avoid using building demolition RCA;
Require a paper trail to document the RCA source. It is recognized that keeping
such records may be challenging;
Use a non-ferrous metal detector to determine if aluminum is present and also
visually inspect the RCA prior to use.
277
CHAPTER 6 IMPLICATIONS OF RESEARCH RESULTS ON SPECIFICATIONS
The research results have the following implications on the specifications:
RAP
1. While the resilient modulus and shear strength of RAP is quite appreciable, its
CBR is low (figures 2-12 and 2-15b) and it suffers from significant permanent
deformation – more so than RCA and VA (Table 2-38). The 50% RAP:50% VA
blend fared worse. Therefore, it may be prudent to limit the amount of RAP for use
in unbound layers to avoid premature rutting. Saeed (2008) indicated that while 16
out of 29 DOTs polled allow the use of 100% RAP in unbound layers, 1 prohibits
its use and 5 restrict it to 50% or less. In light of this and Figure 2-15b, limiting
RAP to 50% may be prudent as long as the material meets all other requirements
in the specifications that a VA would satisfy plus a proposed addition as described
below.
2. In light of the discussion above, a minimum CBR of 80% and 60% are proposed as
requirements in the specifications for base and subbase courses, respectively.
This will encourage the material supplier to find a RAP blend with less than 50%
RAP that will still have a high enough ―performance specification‖ in terms of CBR.
The CBR is chosen since it is a test that does not require expensive and
sophisticated equipment and since it is commonly performed in industry.
278
3. If the field dry density and moisture content of RAP will be assessed with the
nuclear gauge, the specifications require moisture offsets to be pre-determined
prior to use.
4. The specifications do not allow use of other types of compaction quality
assurance/quality control tests (e.g., TDR, stiffness-measuring devices) unless
approved by the Engineer.
RCA
1. In terms of CBR (figures 2-12 and 2-14b), shear strength (Table 6-1), stiffness
(Figure 6-1) and permanent deformation (Table 3-38), RCA is a very attractive
alternative to VA. Thus from a mechanical standpoint, 100% RCA should be
allowed in the unbound layers. Saeed (2008) indicated that 21 out of 29 DOTs
polled allow the use of 100% RCA in unbound layers while 2 restrict it to 50% or
less. No reason was provided for the restriction.
Table 6-1 Test results for ―loose‖ and ―dense‖ 100%RCA sheared immediately after
consolidation (after Selvarajah, 2010)
Relative
Normal
Peak
Critical State
Compaction Stress
Friction
Shear
Friction
Shear
Angle
Strain
Angle
Strain
(%)(1)
(kPa)
(degrees)
(%)
(degrees)
(%)
68.3
56.6
3.7
45.5
12.8
101.6
55.6
2.2
42.6
12.8
95
135.2
47.5
3.7
42.2
12.8
268.8
44.2
3.3
39.8
12.8
68.3
62.8
1.1
43.7
12.8
101.6
58.4
0.73
43.2
12.8
100
135.2
54.4
1.5
40.2
12.8
268.8
48.3
1.8
41.5
12.8
Notes:
(1) Based on Modified Proctor
279
(2) Gradation of RCA is parallel to that shown in Figure 3-6 with a
maximum particle size of 4.75 mm.
700
8.6%/1893
11.3%/1881
500
14.7%/1857
Mr (MPa)
600
400
300
200
100
0
0
3
6
9
12
15
Loading Sequence No.
Figure 6-1 Effect of water content on Mr for RCA (Legend 3shows the molding water
contents and dry densities in kg/m )
2. RCA has the potential to chemically react and cause pavement distress. Potential
distresses include (a) Alkali silica reaction (ASR); (b) Alkali carbonate reaction
(ACR); (c) Sulfate attack; (d) Tufa formation and (e) High pH leading to corrosion
of aluminum if present. For the Hawaiian basaltic based RCA, it was shown that
tufa formation is unlikely. ACR can occur only for specific aggregate types. ASR
can occur if mixed with RG and this should be avoided. Therefore, sulfate attack
and corrosion of aluminum are two distresses that need to be addressed in the
specifications.
(a) Although challenging to enforce, RCA with known prior distresses such as
ASR, sulfate attack, etc. shall not be allowed.
280
(b) Use of RCA adjacent to RG shall be prohibited to avoid ASR.
(c) Sulfate attack is due to exposure of RCA to high sulfate bearing soils or
ground water which results in the formation of expansive products. To
prevent sulfate attack, designers should ascertain that the surrounding soil
and ground water have low concentrations of sulfates. It is an issue that
should be addressed at the design stage.
It is proposed that the
specifications prohibit the use of RCA if the ground water is brackish (i.e.;
near the ocean) as the salt ions in seawater are rich in sulfates.
(d) Dissolution of RCA raises the pH of the infiltrating water. If the RCA is
contaminated with aluminum metal or aluminum pipes are in the vicinity, the
aluminum can corrode leading to the formation of aluminum hydroxide and
hydrogen gas; both of which can produce expansion. As such, its must be
prohibited near aluminum infrastructure.
In addition, the specifications
should prohibit any aluminum contamination. The engineer should have the
right to use a non-ferrous metal detector to detect aluminum in an RCA pile.
If found, the Engineer should have the right to reject that pile.
3. If the field dry density and moisture content of RCA will be assessed with the
nuclear gauge, the specifications require moisture offsets to be pre-determined
prior to use.
281
4. The presence of RCA in water profoundly increases the pH of the water. As such,
RCA should not be used in drainage fill applications, including drains behind
retaining walls, foundation drains, drainage blankets, and French drains.
RG
The RG obtained was crushed to a very fine gradation (Figure 2-1). This gradation
renders its use as a base or sub-base course rather limited unless it is blended with VA.
Blending RG containing a significant amount of fines with VA may be hazardous as the
fines can cause skin irritation and appropriate safety procedures should be adopted. The
need for such safety procedures has hindered its use as an aggregate on a more
widespread basis. RG could have acceptable engineering characteristics for use as fill as
discussed below.
1. The shear strength of pure RG is reasonably high as seen in Table 6-2.
In
addition, the resilient modulus of 30%RG:70%VA is not insignificant as shown in
Figure 6-2.
2. The CBR of RG has been presented in Figure 2-12 and 2-16b. For RG/VA blends,
there was no clear trend in the variation of CBR with %RG. Because the CBR of
25% RG:75%VA did not exceed 80%, it is recommended to limit its proportion to
not more than 10% in the base course and 25% in the subbase course and fill.
3. From a chemical perspective, crushed RG is mostly silica and its use with RCA is
prohibited in the specs to avoid the risk of ASR. Combinations of RAP and RCA
282
are allowed but not RAP and RG as the mechanical properties of these two
materials are both inferior to VA and combining two inferior materials just does not
make good engineering sense.
Table 6-2 Test results for ―loose‖ and ―dense‖ as-received 100%RG in direct shear (Ooi
et al., 2008)
Relative
Normal
Peak
Compaction Stress
Friction
Shear
Angle
Strain
(%)(1)
(psf)
(degrees)
(%)
963
42.0
10.0
1608
42.5
15.5
85
2899
42.2
13.1
5481
40.6
12.9
963
60.7
6.0
1608
58.6
5.8
95
2899
53.9
7.2
5481
50.3
11.5
Notes:
(1) Based on Modified Proctor.
(2) Gradation of RG tested is the as-received gradation (Figure 2-1)
scalped on the 6.35 mm sieve since the maximum particle size limit is
one-tenth the diameter of the shear box (63.5 mm). Scalping was
performed in accordance with CALTRANS California Test 105 (1978).
Scalping did not significantly alter the as-received gradation since only 2%
of the RG is between 6.35 and 9.5 mm.
283
500
9.8%/2024
11.4%/2021
400
Mr (MPa)
14.1%/2008
300
200
100
0
0
3
6
9
Loading sequence No.
12
15
Figure 6-2 Effect of water content on Mr for
30%RG:70%VA (Legend shows the molding
water contents and dry densities in kg/m3). Gradation tested is shown in Figure 2-22.
General
In summary, the following maximum recycled material content is recommended for the
various applications.
284
Table 6-3 Summary of maximum allowable recycled materials as a percent by dry
weight of the total composite aggregate weight for various highway applications
Highway Application
Maximum Allowable Percent by Weight (%)
Cullet
RAP
RCA1
Untreated Permeable Base2
0
0
0
Untreated Base
10
50
100
Subbase
25
50
100
Structure Backfill
25
50
100
Non-Critical3 Trench Backfill
100
100
100
4
Critical Trench Backfill
25
50
100
Granular Material for Embankment
25
50
100
5
Drainage Fill Applications
100
100
0
Notes
1)
Use of RCA shall not be permitted within 10 feet of any metal (especially
aluminum) pipe or structure and shall not be used within 3 feet of the ground
water table nor below the ground water table.
2)
Use of recycled material in untreated permeable base is not allowed because
the untreated permeable base particles are very uniform and very large.
Large particles of cullet and RCA can crush. RAP can deform readily due to
the lubricating effect of asphalt and has the lowest measured CBR of the
three recycled materials.
3)
―Non-critical‖ trench backfill refers to the portion of a trench backfill that is
more than 5 feet below the road surface or the entire portion of a trench
backfill that is in an area not subject to traffic surcharge.
4)
―Critical‖ trench backfill refers to the portion of a trench backfill that is 5 feet or
less below the road surface and that is subject to surcharge, and the entire
portion of a trench backfill that is in an embankment.
5)
Drainage fill applications include, drains behind retaining walls, foundation
drainage, drainage blankets and French drains.
In addition, the following have been included in the specifications:
A.
Deleterious and prohibited materials are defined and procedures for limiting them
are provided.
B.
Recycled materials shall be tested for gradation and results submitted to the
Engineer. The Engineer shall be notified to visually inspect the recycled material
stockpile prior to use.
C.
The Contractor shall submit a blended aggregate design prior to use or prior to
changing either the source or amount originally approved. For aggregate blends,
285
the Contractor shall submit the means and method on how uniform mixing of the
recycled and virgin aggregates is ensured.
allowed.
286
Blending at the job site is not
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Transportation Research Board, No. 1874, Transportation Research Board of the
National Academies, Washington, D.C., 2004, pp. 47–56.
Yau, A. and Von Quintus, H. Study of LTPP Laboratory Resilient Modulus Test
Data and Response Characteristics. Report No. FHWA-RD-02-051, Federal
Highway Administration, McLean, VA., 2002.
Yu, X. and Drnevich, V.P. Soil Water Content and Dry Density by Time Domain
Reflectometry.
Journal of Geotechnical and Geoenvironmental Engineering.
130(9), 2004. pp. 922 – 934.
Zhang, J., M. Klasky, and B.C. Letellier. The Aluminum Chemistry and Corrosion
in Alkaline Solutions. Journal of Nuclear Materials. Vol. 384, 2009, pp 175-189.
313
APPENDIX
This section contains sections from the 2005 State of Hawaii Department of
Transportation‘s Standard Specifications that have been modified to incorporate
the use of the three recycled materials addressed in this research. Proposed
modifications are annotated below. In addition, two entirely new sections are
proposed for consideration for adoption. They include:
1.
2.
Section 719 RECYCLED CONCRETE AGGREGATE (RCA) AND
RCA-MADE MATERIALS and
Section 720 RECLAIMED ASPHALT PAVEMENT (RAP) AND RAPMADE MATERIALS
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SECTION 203 - EXCAVATION AND EMBANKMENT
203.01 Description.
This section describes excavating, hauling, and
disposing of surplus excavated material; and placing and compacting specified
materials necessary to construct project.
Roadway excavation includes excavating and compacting, or disposing of,
all materials of whatever character encountered in the work.
For terminology used in this section, refer to Section 101 – Terms,
Abbreviations and Definitions and ASTM D 653.
203.02
Materials.
Cullet and Cullet-Made Materials
717
Recycled Concrete Aggregate (RCA) and RCA-Made Materials
719
Reclaimed Asphalt Pavement (RAP) and RAP-Made Materials
720
Embankment material shall include mixture of excavated, selected, or borrow
excavated material, or combination thereof, and cullet. When cullet is not
produced on the project island, or material unit price of cullet is greater than
material unit price of virgin material, cullet may be excluded. Before excluding
cullet, submit availability and pricing documentation. one type of the following
recycled materials [cullet, reclaimed asphalt pavement (RAP) or recycled
concrete aggregate (RCA)]. Use of two or more types of recycled materials shall
not be allowed except a three-way combination of soil, RAP and RCA is
permissible. Recycled materials may be excluded when it is not produced on the
project island, its material unit price is greater than the material unit price of
borrow or it cannot be blended in any proportion with borrow material so as to
meet the gradation requirements of Section 703.24.
Unless otherwise indicated in the contract documents, the following
definitions shall apply to this section:
(A)
Excavated Material: All material excavated from project site for
roadway construction.
(B)
Selected Material: Suitable excavated material for specific use
from areas within the highway right-of-way.
(C)
Borrow Excavated Material: Accepted materials from designated
borrow sources outside right-of-way or excavation limits, conforming to
requirements of Subsection 106.02 - Material Sources. Borrow excavated
material shall conform to size and quality indicated in the contract
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documents. When the contract documents do not indicate size or quality,
borrow material shall be of quality suitable for intended purpose. Borrow
material shall be free of roots and other organic matter, garbage, trash,
junk, and other deleterious material.
203.03 Construction. Clear and grub in accordance with Section 201 - Clearing
and Grubbing, before excavating. Excavate and construct embankment for road,
road intersections, and road entrances to a smooth and uniform surface.
Excavate so as not to disturb material outside limits of slopes or limits of grading.
(A)
Excavation.
(1) General. Obliterate old roadways in accordance with Section 202 Removal of Structures and Obstructions. Blasting will not be allowed.
When encountering possible archaeological, historical, or burial site
findings, comply with requirements of Subsection 107.13(B) - Archaeological,
Historical, and Burial Sites.
(2) Widening or Flattening Cut Slopes. Submit proposed locations for
widening or flattening planned cut slopes to obtain material required for the
following:
(a) Constructing embankment.
(b) Precluding opening unsightly borrow pits.
(c) Increasing stability of cut slopes.
Do not proceed with proposed slope widening or flattening until the
Engineer accepts proposed locations. Steepening of cut slopes will not be
allowed.
(3) Cut Slopes. Round tops and ends of cut slopes in accordance with the
contract documents.
Finish soil cut slopes true and straight in accordance with slope lines
and grades indicated in the contract documents.
Finish cut slopes that are in rock excavation, in a rough condition, with
debris and loose material removed. When completed, the average plane of
excavated slopes shall conform to slopes indicated in the contract
documents. No points shall vary from planned slopes by more than 6 inches
when measured at right angles to slope.
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(4) Subexcavation. When excavation to finished grade results in subgrade or
slopes of unsuitable material as defined in Subsection 101.03 - Definitions,
the Engineer will require the following:
(a) Removing unsuitable material.
(b) Backfilling to finished grade with acceptable material in accordance
with Subsection 203.03(C) - Embankment Construction.
Notify the Engineer two weeks prior to start of subexcavation
operations. The Engineer will perform necessary cross-sectional
measurements before authorizing backfill placement.
When relative compaction of original ground is less than compaction
specified in Subsection 203.03(C)(3) - Compaction of Cut Areas and
Embankments With Moisture and Density Tests and Subsection 203.03(C)(4)
- Compaction of Embankments Without Moisture and Density Tests, compact
upper 6 inches of exposed original ground in accordance with those
subsections.
Unsuitable material shall become property of the Contactor and
disposal of unsuitable material shall be at no increase in contract price or
contract time.
(B) Excavated Material.
(1) Selected Material. Use selected material for the following:
(a) Embankment fill.
(b) Finishing top portion of roadbed.
(c) Constructing roadbed shoulders.
(d) Structure backfill.
(e) Constructing berms.
(f) Erosion control.
(g) Landscaping.
(h) Other purposes in accordance with the contract documents.
Place selected material on roadbed in accordance with Subsection
203.03(C) - Embankment Construction and selected topsoil for erosion
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control in accordance with Section 209 - Temporary Water Pollution, Dust,
and Erosion Control.
Keep selected material in place until it can be hauled and
compacted in its final position. If allowed by the contract documents,
selected material may be stockpiled at locations accepted by the
Engineer, for later placement in final position.
(2) Borrow Excavated Material. Arrange to obtain borrow excavated
material and pay costs involved in accordance with Subsection 106.02 Material Sources. Submit certified test data demonstrating borrow
excavated material to be incorporated in the work conforms to the contract
documents. Acceptance of test data will be subject to field verification
testing by the Engineer. Notify the Engineer 20 working days before
opening borrow areas.
Control of borrow excavated material will be in accordance with
Section 106 - Material Restrictions and Requirements.
Excavate to dimensions and elevations established for borrow pit.
Remove borrow excavated material after the Engineer completes staking
out and cross sectioning of borrow excavated and in-place sites for
measurement and payment purposes. Establish and specify finished
borrow areas approximately true to line and grade. Complete finished
borrow areas so that no water will collect or stand therein.
Place selected material in fill before placing borrow excavated
material.
(3) Surplus Selected Material. Unless otherwise indicated in the contract
documents, and not over soft ground, use surplus selected material when
and in locations accepted by the Engineer to do the following: widen
embankments uniformly or flatten slopes; dispose of at Engineer‘s
designated locations. Dispose of surplus selected material below adjacent
roadbed grade. Complete embankments before disposing of surplus
selected material.
When indicated in the contract documents, the quantity of surplus
selected material is approximate only. Replace shortage of material
caused by premature disposal of surplus selected material at no increase
in contract price or contract time.
Upon completion of disposal operations, grade disposal area to
provide level surface. Unused selected material shall become the
Contractor‘s property. Supply topographic map of disposal area.
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(4) Highly Sensitive Soil. When soil having high moisture content loses
its stability and becomes plastic or muddy, excavate with the least
manipulation or churning of soil.
(C) Embankment Construction.
(1) General. Strip live, dead, or decayed vegetation, rubbish, debris, and
other foreign material from ground surface on which embankment is to be
placed. When embankment is required on existing slopes steeper than five
horizontal to one vertical, bench those areas as work is brought up in layers.
Construct bench of sufficient width to permit operation of placing and
compacting equipment. Use suitable excavated or borrow material, and cullet,
or combination thereof in accordance with Section 703.24 in embankment
construction. Use of embankment material containing cullet will not be
allowed on surface of embankment. Placement of rocks, broken concrete, or
other solid materials will not be allowed in embankment areas where deep
foundations, such as driven piles or drilled shafts, are to be placed.
When soft or swampy ground condition is encountered that cannot support
weight of trucks or other hauling equipment, lower part of fill may be
constructed with a working platform. Construct working platform by either
placing successive loads of gravel, cobbles, and boulders in a uniformly
distributed layer of thickness not greater than necessary; or by using
permeable separator with granular material of adequate thickness to support
construction equipment. Construct remainder of embankment in accordance
with the contract documents.
For minimum depth of 2 feet from subgrade, place embankment material
with maximum size of 6 inches and sand equivalent (SE) of 10 or greater, but
not less than SE of soil material upon which it is placed. Except as otherwise
indicated in the contract documents, embankment material below 2 feet from
subgrade may consist of material with maximum size of 6 inches and SE of
less than 10 but not less than SE of existing soil on which embankment is
placed. Place embankment material in horizontal layers not exceeding 9
inches in loose thickness. Compact as specified before placing next layer.
Manipulate material to ensure uniform density and surface smoothness, as
compaction of each layer progresses. Add or remove water to obtain required
density.
Embankment fill below top 2 feet from subgrade may contain material with
rock fragments, hardpan, or cemented gravel larger than 6 inches but less
than 3 feet in greatest dimension. Place in compacted lifts of thickness not
exceeding approximate size of the rocks and not exceeding 3 feet. Process
embankment material to reduce maximum size of particles so that material
can be placed in specified lifts. Uniformly distribute larger rock throughout
bottom of embankment and place sufficient selected material and other finer
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rock around large material to fill voids and to produce a dense, compact
embankment. Provide earth or fine material to fill voids when not available in
excavation.
The embankment material whether blended or from a single source shall
have a plasticity index not greater than 15% when tested in accordance with
AASHTO T 89 and AASHTO T 90.
Finish embankment slopes, as indicated in the contract documents, to
within plus or minus 3 inches of lines and grades established and such that
slopes contain no unsightly or undue irregularities. Finish top of embankment
surfaces in accordance with Subsection 203.03(D) - Subgrade Preparation.
Replace portions that become displaced or damaged prior to acceptance at
no increase in contract price or contract time.
(2) Relative Compaction Test. Relative compaction test is a procedure for
determining ratio of dry unit weight (density) of in-place soil to maximum dry
unit weight of same soil, as determined by the following methods:
(a) Maximum Dry Unit Weight. Test for maximum dry unit weight in
accordance with AASHTO T 180, Method D. Use Hawaii Test Method
HDOT TM 5 for sample preparation of sensitive soils when so
designated by the Engineer. When oversized materials larger than 3/4
inch exceed 5 percent by weight of total sample, apply corrections to
laboratory dry density in accordance with AASHTO T 224. When
oversized materials larger than 3/4 inch exceed 30 percent, use
compaction procedure specified in Subsection 203.03(C)(4) Compaction of Embankments Without Moisture and Density Tests.
(b) Density of Soil In-Place. Test for soil in-place density in
accordance with Hawaii Test Method HDOT TM 1, HDOT TM 2, and
HDOT TM 3. When using the nuclear gauge to test for the in-place
density of recycled concrete aggregate (RCA) or reclaimed asphalt
pavement or their blends, moisture offsets shall first be determined for
the same material blend that will be used on site. Without the moisture
offset, the nuclear gauge shall not be acceptable for field testing of
RCA, RAP or their blends. Use of other methods of quality assurance
and quality control shall be prohibited unless approved by the
Engineer.
(3) Compaction of Cut Areas and Embankments With Moisture and
Density Tests. Prior to shaping and compacting, condition soil to moisture
content within 2 percent above or below optimum moisture content
determined in accordance with AASHTO T 180. Except as specified in
Subsection 203.03 (C)(4) – Compaction of Embankments Without Moisture
and Density Tests, moisture condition embankment material and place in
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layers not to exceed 9 inches in loose thickness, and compact each layer of
material as specified, before placement of next lift. Determine maximum
density and relative compaction in accordance with Subsection 203.03(C)(2)
– Relative Compaction Test.
In-situ soil or embankment material contained in prism within 2 feet below
subgrade and within width of traveled way, auxiliary lane, and shoulder on
each side shall have relative compaction of 95 percent or more. When in-situ
material within 2 feet below subgrade does not conform to specified relative
compaction, excavate and recompact material until specified relative
compaction is achieved.
Top 6 inches of in-situ material and embankment material below top 2 feet
of subgrade, and beyond traveled way, auxiliary lane, and shoulder prism,
shall have relative compaction of at least 90 percent. When in-situ material
cannot be compacted to 90 percent, provide working platform to allow 90
percent compaction of first lift.
(4) Compaction of Embankments Without Moisture and Density Tests.
Use trial fill section to determine required degree of compaction and method
to obtain that compaction, for materials with sufficient coarse material that
compaction cannot be determined by Subsection 203.03(C)(2) – Relative
Compaction Test. Use trial section to determine type and size of compaction
equipment, lift thickness, and number of passes required to obtain
compaction acceptable to the Engineer.
For rock fill placement in lifts not exceeding 2 feet in loose lift, the
following compaction procedures may be used in lieu of trial section. For rock
sizes not exceeding 9 inches in greatest dimension, place material in 12-inch
loose lift and compact material full width using one of the following methods:
(a)
Two passes of a 50-ton compression-type roller.
(b)
Two passes of a vibratory roller having minimum dynamic
force of 40,000 pounds impact per vibration and minimum
frequency of 1,000 vibrations per minute.
(c)
Eight passes of a 10-ton compression-type roller.
(d)
Eight passes of a vibratory roller having minimum dynamic
force of 30,000 pounds impact per vibration and minimum
frequency of 1,000 vibrations per minute.
Operate compression-type rollers at speeds less than 4 miles per hour
and vibratory rollers at speeds less than 1.5 miles per hour. For rock sizes not
exceeding 14 inches in greatest dimension, place material in 18-inch loose lift
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and compact material full width with increase in number of roller passes in
Subsections (a) and (b) herein by two, and increase number of roller passes
in Subsections (c) and (d) herein by four. For rock sizes not exceeding 18
inches in greatest dimension, place material in 24-inch loose lift and compact
material full width with increase in number of roller passes in Subsections (a)
and (b) herein by four, and increase number of roller passes in Subsections
(c) and (d) herein by eight. Use trial fill section as specified in this subsection
for embankment with rock sizes 19 to 36 inches in maximum dimension.
(D) Subgrade Preparation. Prepare subgrade to required density, cross section,
and grade.
(1) General. Prepare subgrade after completing and backfilling drainage
facilities and structures and compacting earthwork.
Remove rocks or lumps and fill voids with suitable materials. Material used
to fill voids shall conform to specified material to be placed on subgrade.
(2) Density Requirement. Compact finish subgrade to relative compaction of
95 percent for depth of 6 inches immediately before placing subsequent
material thereon.
(3) Surface Tolerances of Subgrade. Finish subgrade upon which
pavement structure is to be placed shall not vary more than 0.04-foot above
or below theoretical grade.
203.04 Measurement. The Engineer will measure:
(A) Roadway excavation per cubic yard. The Engineer will compute quantities
of roadway excavation by average end area method and centerline distances.
Curvature correction will not be applied to quantities within roadway prism, as
indicated in the contract documents. In computing excavation quantities from
outside the roadway prism, where roadway centerline is used as a base,
curvature correction will be applied when centerline radius is 1,000 feet or
less.
When roadway excavation quantities by average end area method cannot
be computed due to the nature of a particular operation or changed
conditions, the Engineer will determine and use computation method that will
produce an accurate quantity estimate.
(B) Borrow excavated material per cubic yard. The Engineer will compute
quantities of borrow material incorporated into the work on a volume basis,
using average end area method in place at work site.
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(C) Selected material for planting soil and selected material for decorative
boulder will be paid on a lump sum basis. Measurement for payment will not
apply.
203.05 Payment. The Engineer will pay for the accepted pay items listed below
at the contract price per pay unit, as shown in the proposal schedule. Payment
will be full compensation for the work prescribed in this section and the contract
documents.
The Engineer will pay for each of the following pay items when included in
the proposal schedule:
Pay Item
Pay Unit
Roadway Excavation
Cubic Yard
The Engineer will pay for:
(A) 15 percent of the contract bid price upon completion of obliterating old
roadways and hauling.
(B) 30 percent of the contract bid price upon completion of preparing
subgrade.
(C) 40 percent of the contract bid price upon completion of placing selected
material in final position, rounding of slopes, and using water for compaction.
(D) 15 percent of the contract bid price upon completion of disposing of
surplus excavation material.
Borrow Excavated Material
Cubic Yard
The Engineer will pay for:
(A) 10 percent of the contract bid price upon completion of staking out and
cross sectioning existing condition at borrow excavated and in-place sites and
establishing borrow area.
(B) 5 percent of the contract bid price upon completion of providing, replacing,
and maintaining temporary and permanent fencing, and confining livestock.
(C) 15 percent of the contract bid price upon completion of all necessary
storing and processing of borrow material.
(D) 15 percent of the contract bid price upon completion of watering and
hauling material to work site.
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(E) 20 percent of the contract bid price upon completion of placing, grading,
and compacting material in accordance with contract requirements at work
site.
(F) 15 percent of the contract bid price upon completion of restoring and
regrading borrow area.
(G) 10 percent of the contract bid price upon completion of staking out and
cross sectioning final condition at borrow excavated and in-place sites.
(H) 10 percent of the contract bid price upon completion of removing and
disposing of excess and unsuitable material from work site.
Selected Material for Planting Soil
Lump Sum
Selected Material for Decorative Boulder
Lump Sum
The Engineer will pay for accepted quantities of subexcavation, as
roadway excavation at the contract unit price per cubic yard, when ordered by
the Engineer, for work prescribed in Subsection 203.03(A)(4) – Subexcavation.
Payment will be full compensation for the work prescribed therein and in the
contract documents.
The Engineer will pay for accepted quantities of unlined gutter excavation
as roadway excavation at the contract unit price per cubic yard, when gutter is
located as follows: within median area of a divided highway; and between
roadbed shoulder and adjacent cut slope. Payment will be full compensation for
removing and disposing of excavated material; backfilling and compacting; and
for the work prescribed in the contract documents.
The Engineer will not pay for stockpiling selected material, placing
selected material in final position, or placing selected material in windrows along
tops of roadway slopes for erosion control work, separately and will consider the
cost as included in the unit prices for the various excavation contract pay items.
The cost is for work prescribed in this section and the contract documents.
The Engineer will not pay for selected material from ditch, channel, or
structure excavation, when used instead of borrow excavation.
The Engineer will not pay for overhaul separately and will consider the
cost as included in the unit prices for the various excavation contract pay items.
The cost is for work prescribed in this section and the contract documents.
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The Engineer will not pay for embankment separately and will consider the
cost as included in the unit price for roadway excavation. The cost is for work
prescribed in this section and the contract documents.
END OF SECTION 203
325
SECTION 204 - EXCAVATION AND BACKFILL FOR MISCELLANEOUS
FACILITIES
204.01 Description. This section describes the following:
(A) Excavating and backfilling to depths and lines established for foundations
of roadway and sign lighting standards, and traffic signal standards.
(B) Excavating and backfilling trenches for utilities pipes (including water,
sewer, telephone, oil, and gas lines) and conduits (including roadway and
sign lighting, traffic signal, and other communications systems).
(C) Excavating and backfilling for water and sewer manholes and
appurtenances.
(D) Disposing of surplus material from excavations.
Excavating and backfilling for water and sewer pipes, manholes, and
appurtenances are described further in Section 624 – Water System and Section
625 – Sewer System.
204.02 Materials.
Structure Backfill Material
703.20
Trench Backfill Material
703.21
Geotextiles for Underdrain Applications
716.03
Cullet and Cullet-Made Materials
717
Recycled Concrete Aggregate (RCA) and RCA-Made Materials
719
Reclaimed Asphalt Pavement (RAP) and RAP-Made Materials
720
Structure and trench backfill material shall include mixture of aggregate
and cullet. When cullet is not produced on the project island, or material unit
price of cullet is greater than material unit price of structure backfill or greater
than material unit price of trench backfill, cullet may be excluded for that backfill
application. Before excluding cullet, submit availability and pricing
documentation. consist of either 100% virgin aggregate, or of a mixture of virgin
aggregate and one type of the following recycled materials [cullet, reclaimed
asphalt pavement (RAP) or recycled concrete aggregate (RCA)]. Use of two or
more types of recycled materials shall not be allowed except a three-way
combination of virgin aggregate, RAP and RCA is permissible. Recycled
materials may be excluded when it is not produced on the project island, its
326
material unit price is greater than the material unit price of virgin aggregate or it
cannot be blended in any proportion with virgin aggregate so as to meet the
gradation requirements of Sections 703.20 and 703.21.
Trench gravel backfill material shall conform to AASHTO M 43, size
number 67. When tested in accordance with AASHTO T 96, the LA abrasion
shall not exceed 40 percent at 500 revolutions.
Controlled Low Strength Material (CLSM) in accordance with Section 314
– Controlled Low Strength Material (CLSM) for Utilities and Structures may be
used in place of trench and structure backfill material, subject to the Engineer‘s
acceptance. Where CLSM is allowed, provide drainage system to accommodate
underground water seepage. CLSM will not be allowed as trench backfill when
installing aluminum and aluminum-coated pipe conduits.
Provide plastic marking tape that is acid and alkali-resistant polyethylene
film, 6 inches wide with minimum thickness of 0.004 inch. Provide tape with
minimum strength of 1750 psi lengthwise and 1500 psi crosswise. Manufacture
tape with integral wires, foil backing, or other means to enable detection by a
metal detector when tape is buried up to 3-feet deep. Manufacture tape
specifically for marking and locating underground utilities. Provide metallic core
of tape encased in a protective jacket or provided with other means to protect it
from corrosion. Tape shall conform to the following colors and shall bear a
continuous printed inscription describing the specific utility: Red: Electric; Yellow:
Gas, Oil, Dangerous Materials; Orange: Telephone, Telegraph, Television,
Police, and Fire Communications; Blue: Water System; Green: Sewer Systems.
204.03 Construction.
(A) Structure and Trench Excavation.
(1) General. Notify the Engineer 10 working days before excavating
for structures and trenches.
The Contractor shall be responsible for the stability of
temporary open cuts during construction of structures or trenches
and shall take appropriate measures to meet OSHA requirements.
Excavate in such a manner as to prevent damage to
pavements, sidewalks, structures, landscaping, and other
improvements. Excavate immediately before installation of conduit
and other appurtenances. Stockpile excavated material in a
location that shall not cause damage, obstruct vehicular and
pedestrian traffic, or interfere with surface drainage.
327
In excavation operations, do not disturb ground below
elevations indicated in the contract documents. If ground below
elevations indicated in the contract documents is disturbed,
excavate disturbed ground until undisturbed ground is reached.
Backfill this area with Class D concrete until required foundation
elevation is reached.
Keep foundation excavation dry by draining, bailing,
pumping, or driving sheathings.
When material from excavation does not meet quality
requirements specified for backfill in accordance with Subsection
204.02 – Materials, furnish conforming material, as required.
Deposit remaining structure or trench excavation material
that is not used as backfill, in roadway embankments in accordance
with Subsection 203.03(B)(1) – Selected Material. Dispose of
surplus selected material in accordance with Subsection
203.03(B)(3) – Surplus Selected Material.
(2) Foundation Treatment. When footing concrete or masonry is
to rest upon rock, fully uncover rock and remove rock surface to a
depth sufficient to expose sound rock. Roughly level rock surface or
cut to steps; and roughen rock surface.
Grout seams in rock under pressure. The Engineer will pay
cost in accordance with Subsection 104.02 - Changes.
While excavating for non-pile foundations where footing
concrete or masonry is to rest on an excavated surface other than
rock, do not disturb excavation bottom. Remove foundation material
to final grade immediately prior to placing concrete or masonry.
Complete driven pile foundation excavation to footing bottom
before driving piles therein. Remove excess materials remaining in
the excavation, after pile driving, to footing bottom elevation.
In pile foundations, excavating a sufficient distance below
footing bottom will be allowed, as indicated in the contract
documents, at no increase in contract price or contract time. When
ground surface has risen above plan grade after pile driving,
remove surplus material at no increase in contract price or contract
time. When ground surface is below plan grade after pile driving,
backfill and compact to plan grade with acceptable material, at no
increase in contract price or contract time.
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(3) Inspection. When the Engineer needs to determine character
of foundation material, excavate test pits, drill test borings, and
perform foundation bearing tests in accordance with Section 211 Exploratory Work at Structure Footings.
When structure excavation to foundation grade is completed,
request that the Engineer inspect and accept foundation elevation
and character before placing concrete or masonry and reinforcing
steel in the footing.
(B) Structure and Trench Backfill. Do not deposit fill material against
back of foundations and manholes until test samples indicate that
concrete has developed strength required in Subsection 503.03(E) –
Loading.
Cure test samples under conditions similar to those affecting the
structure. Continue backfilling so that excessive unbalanced loads are not
introduced against the structure.
Place backfill material in uniform horizontal layers not exceeding 8
inches in loose thickness, before compaction. Moisten and compact each
layer of backfill until relative compaction of not less than 95 percent is
achieved in accordance with Subsection 203.03(C)(2) – Relative
Compaction Test. The Engineer may reduce 95 percent compaction
requirement in situations where such compaction is not feasible.
When the Engineer cannot use field density test, compact each
layer of backfill with vibratory or other accepted equipment on granular
backfill material.
Compaction of backfill material by ponding or jetting will not be
allowed.
Where bottom of utility pipe is located within 12 inches or below
normal ground water level, use trench gravel backfill material to at least 12
inches above pipe or to bottom of pavement structure. Gravel material
shall be completely encapsulated by geotextile conforming to Subsection
716.03 - Geotextiles for Underdrain Applications.
When required, place sufficient fill at structures, utility pipes, and
conduits ahead of other grading operations to permit public traffic to cross.
Compact backfill material in the following areas to a relative
compaction of not less than 90 percent:
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(1) Footings not beneath surfacing.
(2) Other locations where the contract documents indicate 90
percent relative compaction for structure or trench backfill.
Place plastic marking warning tapes for appropriate type of utility
directly above pipe, within a depth of 3 feet from finish grade, unless
otherwise indicated in the contract documents.
204.04 Measurement.
(A) Trench excavation will be paid on a lump sum basis. Measurement for
payment will not apply.
(B) Trench backfill will be paid on a lump sum basis. Measurement for
payment will not apply.
204.05 Payment. The Engineer will pay for the accepted pay items listed below
at the contract price per pay unit, as shown in the proposal schedule. Payment
will be full compensation for the work prescribed in this section and the contract
documents.
The Engineer will pay for each of the following pay items when included in
the proposal schedule:
Pay Item
Pay Unit
Trench Excavation for__________________
Lump Sum
Trench Backfill for_____________________
Lump Sum
The Engineer will pay for removal of material from depths greater than 3
feet below depths indicated in the contract documents in accordance with
Subsection 104.02 - Changes.
The Engineer will not pay for trench excavation for roadway and sign
lighting and traffic signal system conduits separately and will consider the cost for
those items as included in the contract prices for the various contract pay items.
The cost is for work prescribed in this section and the contract documents.
The Engineer will not pay for structure excavation and structure backfill for
miscellaneous facilities separately and will consider the cost for those items as
included in the contract prices for the various contract pay items. The cost is for
the work prescribed in this section and the contract documents.
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The Engineer will not pay for excavation and backfill for water and sewer
manholes and appurtenances separately and will consider the cost for those
items as included in the contract prices for the various contract pay items. The
cost is for the work prescribed in this section and the contract documents.
END OF SECTION 204
331
SECTION 205 - EXCAVATION AND BACKFILL FOR BRIDGE AND
RETAINING STRUCTURES
205.01 Description. This section describes the following:
(A) Excavating and backfilling to depths and lines established for bridge,
overhead-mounted expressway sign, and retaining (reinforced concrete or
cement rubble masonry) structure foundations.
(B) Other excavating and backfilling specifically designated in the contract
documents as structure excavations and backfills.
(C) Disposing of surplus material from structure excavations.
(D) Bailing, draining, sheathing, and constructing cofferdams, if necessary,
and subsequently removing sheathing and cofferdams.
205.02 Materials.
Filter Material
703.18
Structure Backfill Material
703.20
Cullet and Cullet-Made Materials
717
Recycled Concrete Aggregate (RCA) and RCA-Made Materials
719
Reclaimed Asphalt Pavement (RAP) and RAP-Made Materials
720
Structure backfill material shall include mixture of aggregate and cullet.
When cullet is not produced on the project island, or material unit price of cullet is
greater than material unit price of structure backfill, cullet may be excluded.
Before excluding cullet, submit availability and pricing documentation. consist of
either 100% virgin aggregate, or of a mixture of virgin aggregate and one type of
the following recycled materials [cullet, reclaimed asphalt pavement (RAP) or
recycled concrete aggregate (RCA)]. Use of two or more types of recycled
materials shall not be allowed except a three-way combination of virgin
aggregate, RAP and RCA is permissible. Recycled materials may be excluded
when it is not produced on the project island, its material unit price is greater than
the material unit price of virgin aggregate or it cannot be blended in any
proportion with virgin aggregate so as to meet the gradation requirements of
Section 703.20.
Controlled Low Strength Material (CLSM) in accordance with Section 314
– Controlled Low Strength Material (CLSM) for Utilities and Structures may be
used in place of structure backfill material, subject to the Engineer‘s acceptance.
332
Where CLSM is allowed, provide drainage system to accommodate underground
water seepage.
205.03 Construction.
(A) Structure Excavation.
(1) General. Notify the Engineer 10 working days before excavating
for structures.
The Contractor shall be responsible for the stability of
temporary open cuts during construction of structures or trenches
and shall take appropriate measures to meet OSHA requirements.
In structure excavation operations, do not disturb ground
below elevations indicated in the contract documents. If ground
below elevations indicated in the contract documents is disturbed,
excavate disturbed ground until undisturbed ground is reached.
Backfill this area with Class D concrete until required foundation
elevation is reached.
Keep foundation excavation dry by draining, bailing,
pumping, driving sheathings; or by constructing cofferdams and
cribs.
When material from excavation does not meet quality
requirements specified for backfill in accordance with Subsection
205.02 - Materials, furnish conforming material, as required.
Deposit remaining structure excavation material that is not
used as structural backfill, in roadway embankments in accordance
with Subsection 203.03(B)(1) – Selected Material. Dispose of
surplus selected material in accordance with Subsection
203.03(B)(3) – Surplus Selected Material.
(2) Cofferdams. Construct cofferdams for foundation construction
to depths well below bottom of footings to ensure stability and to
adequate heights to seal off all water. Brace well and make as
watertight as necessary for proper performance of work that must
be conducted inside cofferdam. Provide interior cofferdam
dimensions so as to give sufficient clearance for driving piles,
constructing forms, and when not placing seal, permitting pumping
from outside the forms.
When clearance indicated in the contract documents
between outside line of footings and piles, or interior walls or
333
surfaces are insufficient to permit pile driving or form building, the
Contractor may enlarge cofferdams to provide sufficient clearance.
The Engineer will consider enlargement exceeding one foot outside
footing dimensions indicated in the contract documents as being for
the sole purpose of expediting work of the Contractor and of no
value to the State. The Engineer will not include for payment,
excavation and backfill that exceed described limits.
Correct or enlarge cofferdams that are tilted or moved out of
position during the process of sinking. Conduct such work at no
increase in contract price or contract time.
In tidal waters or in streams at a time of probable flood, vent
cofferdam walls at low water elevation to ensure equal hydrostatic
head both inside and outside of cofferdam during pouring and
setting of seals.
Shoring in cofferdams that will induce stress, shock, or
vibration in the permanent structure will not be allowed.
When permitted, cross struts or bracing may extend through
foundation concrete. Such struts or bracing below low water will be
allowed to remain in place. Remove struts or bracing above low
water. Fill volume with concrete of the same mix as that specified
for surrounding concrete.
If requested by the Engineer, submit drawings and design
calculations, signed by Hawaii Licensed Structural Engineer,
showing proposed method of cofferdam construction and other
details left open to the Contractor‘s choice or not fully indicated in
the contract documents for substructure work.
After completion of structure, remove cofferdams, including
sheathing and bracing, to a depth of 1 foot below streambed.
Remove cofferdams in a manner that will not disturb or damage
finished concrete or masonry.
(3) Foundation Treatment. When footing concrete or masonry is
to rest upon rock, fully uncover rock and remove rock surface to a
depth sufficient to expose sound rock. Roughly level rock surface or
cut to steps; and roughen rock surface.
Grout seams in rock under pressure. The Engineer will pay
cost in accordance with Subsection 104.02 - Changes.
334
While excavating for non-pile foundations where footing
concrete or masonry is to rest on an excavated surface other than
rock, do not disturb excavation bottom. Remove foundation material
to final grade immediately prior to placing concrete or masonry.
Complete driven pile foundation excavation to footing bottom
before driving piles therein. Remove excess materials remaining in
the excavation, after pile driving, to footing bottom elevation.
In pile foundations, excavating a sufficient distance below
footing bottom will be allowed, as indicated in the contract
documents, at no increase in contract price or contract time. When
ground surface has risen above plan grade after pile driving,
remove surplus material at no increase in contract price or contract
time. When ground surface is below plan grade after pile driving,
backfill and compact to plan grade with acceptable material, at no
increase in contract price or contract time.
(4) Inspection. When the Engineer needs to determine character
of foundation material, excavate test pits, drill test borings, and
perform foundation bearing tests in accordance with Section 211 Exploratory Work at Structure Footing.
When structure excavation to foundation grade is completed,
request that the Engineer inspect and accept foundation elevation
and character before placing concrete or masonry and reinforcing
steel in the footing.
(B) Structure Backfill. Place structure backfill material A behind bridge
abutments, wingwalls, and retaining walls. Do not deposit fill material
against back of concrete abutments, piers, concrete retaining walls, and
foundations until test samples indicate that concrete has developed
strength required in Subsection 503.03(E) - Loading.
Cure test samples under conditions similar to those affecting the
structure. Continue backfilling so that excessive unbalanced loads are not
introduced against the structure.
When spreading and compacting backfill, do not operate heavy
equipment closer to abutment or retaining walls, than a distance equal to
the height of backfill above top of footing. Compact area remaining, in
layers not more than 4 inches in compacted thickness, with power-driven
hand tampers suitable for material being compacted.
Place backfill material in uniform horizontal layers not exceeding 8
inches in loose thickness, before compaction. Moisten and compact each
335
layer of backfill until relative compaction of not less than 95 percent is
achieved in accordance with Subsection 203.03(C)(2) – Relative
Compaction Test. The Engineer may reduce 95 percent compaction
requirement in situations where such compaction is not feasible.
When the Engineer cannot use field density test, compact each
layer of backfill with vibratory or other accepted equipment on granular
backfill material.
Compaction of backfill material by ponding or jetting will not be
allowed.
When required, place sufficient fill at bridges ahead of other grading
operations to permit public traffic to cross.
Compact structure backfill in the following areas to a relative
compaction of not less than 90 percent:
(1) Footings for slope protection, slope paving, and aprons.
(2) Retaining walls, except portions under surfacing, and crib walls.
(3) Footings not beneath surfacing.
(4) Other locations where the contract documents indicate 90
percent relative compaction for structure backfill.
(C) Filter Material. Place backfill filter material at bridge abutments and
retaining walls in accordance with the contract documents.
Make subgrade as impervious as possible to direct drainage toward
weep holes. Impervious material is defined as materials passing the No.
200 sieve and compacted to minimum 90 percent of maximum density,
when tested in accordance with AASHTO T 180, Method D.
205.04 Measurement.
(A) Structure Excavation. Structure excavation will be paid on a lump
sum basis. Measurement for payment will not apply.
(B) Structure Backfill. Structure backfill for bridge abutments, wingwalls,
and retaining walls will be paid on a lump sum basis. Measurement for
payment will not apply.
(C) Filter Material. Filter material will be paid on a lump sum basis.
Measurement for payment will not apply.
336
205.05 Payment. The Engineer will pay for the accepted pay items listed below
at the contract price per pay unit, as shown in the proposal schedule. Payment
will be full compensation for the work prescribed in this section and the contract
documents.
The Engineer will pay for each of the following pay items when included in
the proposal schedule:
Pay Item
Pay Unit
Structure Excavation for ______________
Lump Sum
Structure Backfill for _________________
Lump Sum
Filter Material
Lump Sum
The Engineer will pay for removal of material from depths greater than 3
feet below depths indicated in the contract documents in accordance with
Subsection 104.02 - Changes.
END OF SECTION 205
337
SECTION 304 - AGGREGATE BASE COURSE
304.01 Description.
This section
aggregate base on a prepared surface.
304.02
describes
furnishing
and
placing
Materials.
Aggregate for Untreated Base
703.06
Water
712.01
Cullet and Cullet-Aggregate Mixtures as Construction Materials
717.01
Cullet Materials for Roadways
717.02
RCA and RCA-Aggregate Mixtures as Construction Materials
719.01
RCA for Roadways
719.02
RAP and RAP-Aggregate Mixtures as Construction Materials
720.01
RAP for Roadways
720.02
Aggregate base course shall consist of either 100% virgin aggregate, or of
a mixture of virgin aggregate and one type of the following recycled materials
[cullet, reclaimed asphalt pavement (RAP) or recycled concrete aggregate
(RCA)]. Use of two or more types of recycled materials shall not be allowed in a
base course except a three-way combination of virgin aggregate, RAP and RCA
is permissible. Recycled materials may be excluded when it is not produced on
the project island, its material unit price is greater than the material unit price of
virgin aggregate or it cannot be blended in any proportion with virgin aggregate
so as to meet the gradation requirements of Section 703.06.
304.03
Construction.
(A)
Hauling and Placing. Haul, deposit, and spread aggregate base
on a prepared surface in a manner that minimizes rutting, uneven
compaction, and segregation. Should segregation occur, remove
segregated material and replace with material conforming to the contract
documents, at no increase in contract price or contract time.
Where compacted thickness is greater than 6 inches, spread and
compact mixture in two or more lifts approximately equal in thickness.
Maximum compacted thickness of one lift shall be 6 inches.
338
(B)
Shaping and Compacting. Prior to shaping, add water uniformly
to aggregate base, as necessary, to obtain moisture content within 2
percent of the optimum moisture content for compaction.
Immediately after spreading aggregate base, shape and compact
each lift across full width using power roller. Roll in direction parallel to
centerline of road. For areas inaccessible to roller, compact using
tampers or compactors.
Compact each lift to produce uniform surface texture and to attain
at least 95 percent of maximum density in accordance with Subsection
203.03(C)(2) - Relative Compaction Test.
Limit surface deviations of finished areas to not more than ½ inch
above or below theoretical grade. Correct surface deviations more than ½
inch above or below theoretical grade by scarifying, adding or removing
material, blading, and compacting. Reshape high or low spots with selfpropelled, pneumatic-tired motor grader. Use graders with wheelbase not
less than 15 feet long and blade not less than 10 feet long.
304.04
Measurement. Aggregate base will be paid on a lump sum basis.
Measurement for payment will not apply.
304.05
Payment. The Engineer will pay for the accepted aggregate base
on a contract lump sum basis. Payment will be full compensation for the work
prescribed in this section and the contract documents.
The Engineer will pay for the following pay item when included in the
proposal schedule:
Pay Item
Pay Unit
Aggregate Base
Lump Sum
END OF SECTION 304
339
SECTION 305 - AGGREGATE SUBBASE COURSE
305.01 Description.
This section describes
aggregate subbase on a prepared surface.
305.02
furnishing
and
placing
Materials.
Aggregate for Subbase
703.06
Water
712.01
Cullet and Cullet-Aggregate Mixtures as Construction Materials
717.01
Cullet Materials for Roadways
717.02
RCA and RCA-Aggregate Mixtures as Construction Materials
719.01
RCA for Roadways
719.02
RAP and RAP-Aggregate Mixtures as Construction Materials
720.01
RAP for Roadways
720.02
Aggregate subbase course shall consist of either 100% virgin aggregate,
or of a mixture of virgin aggregate and one type of the following recycled
materials [cullet, reclaimed asphalt pavement (RAP) or recycled concrete
aggregate (RCA)]. Use of two or more types of recycled materials shall not be
allowed in a subbase course except a three-way combination of virgin aggregate,
RAP and RCA is permissible. Recycled materials may be excluded when it is not
produced on the project island, its material unit price is greater than the material
unit price of virgin aggregate or it cannot be blended in any proportion with virgin
aggregate so as to meet the gradation requirements of Section 703.17.
305.03
Construction.
(A)
Hauling and Placing. Haul, deposit, and spread aggregate
subbase on a prepared surface in a manner that minimizes rutting, uneven
compaction, and segregation. Should segregation occur, remove
segregated material and replace with material conforming to the contract
documents, at no increase in contract price or contract time.
Where compacted thickness is greater than 6 inches, spread and
compact mixture in two or more lifts approximately equal in thickness.
Maximum compacted thickness of one lift shall be 6 inches.
340
(B)
Shaping and Compacting. Prior to shaping, add water uniformly
to aggregate subbase, as necessary, to obtain moisture content within 2
percent of the optimum moisture content for compaction.
Immediately after spreading aggregate subbase, shape and
compact each lift across full width using power roller. Roll in direction
parallel to centerline of road. For areas inaccessible to roller, compact
using tampers or compactors.
Compact each lift to produce uniform surface texture and to attain
at least 95 percent of maximum density in accordance with Subsection
203.03(C)(2) - Relative Compaction Test.
Limit surface deviations of finished areas to not more than ½ inch
above or below theoretical grade. Correct surface deviations more than ½
inch above or below theoretical grade by scarifying, adding or removing
material, blading, and compacting. Reshape high or low spots with selfpropelled, pneumatic-tired motor grader. Use graders with wheelbase not
less than 15 feet long and blade not less than 10 feet long.
304.06 Measurement. Aggregate subbase will be paid on a lump sum basis.
Measurement for payment will not apply.
304.07 Payment. The Engineer will pay for the accepted aggregate subbase
on a contract lump sum basis. Payment will be full compensation for the work
prescribed in this section and the contract documents.
The Engineer will pay for the following pay item when included in the proposal
schedule:
Pay Item
Pay Unit
Aggregate Subbase
Lump Sum
END OF SECTION 305
341
SECTION 306 – UNTREATED PERMEABLE BASE COURSE
306.01 Description. This section describes furnishing and placing untreated
permeable base on a prepared surface.
306.02
Materials.
Coarse Aggregate
703.04(A)
Filler
703.04(B)
Water
712.01
Use of recycled asphalt pavement (RAP), recycled glass cullet and
recycled concrete aggregate (RCA) shall not be allowed in the untreated
permeable base.
306.03
Construction.
(A)
Equipment. Use static steel power rollers weighing not less than
10 tons, with compression on rear wheels of not less than 323 ponds per
inch of tire width.
Use long-bristle brooms.
(B)
Untreated Permeable Base Course Edge Preparation. Before
placing untreated permeable base, construct adjacent embankment areas
to finished surface elevation. Construct embankment in accordance with
Subsection 203.03(C) - Embankment Construction. Provide form or
choker to retain untreated permeable base material by cutting
embankment material as nearly vertical as possible. Position toe of cut at
exterior bottom limit of untreated permeable base material. Dispose of cut
embankment material in accordance with Subsection 201.03(F) - Removal
and Disposal of Material.
(C)
Hauling and Placing. Haul, deposit, and spread untreated
permeable base on a prepared surface in a manner that minimizes rutting,
uneven compaction, and segregation. Should segregation occur, remove
segregated materials and replace with material conforming to the contract
documents, at no increase in contract price or contract time.
Before depositing coarse aggregate, place permeable separator on
subgrade or subbase in accordance with Section 313 – Permeable
Separator.
342
When required compacted thickness is 9 inches or less, place
coarse aggregate in one lift. When required compacted thickness is more
than 9 inches, construct in two or more lifts of approximately equal
thickness.
Construction equipment will not be allowed to make sudden stops,
starts, or turns on coarse aggregate. Spread coarse aggregate using
loader or grader. Place coarse aggregate on permeable separator with at
least 12 inches of material between equipment tires or tracks and
permeable separator. When required thickness is less than 12 inches, limit
size and weight of construction vehicles so that rutting in coarse
aggregate is not greater than 3 inches deep. Only placement, spreading,
and smooth drum, non-vibratory compaction equipment will be allowed on
the first lift above permeable separator.
(D)
Shaping and Compacting. Immediately after spreading coarse
aggregate, shape and compact each lift across full width using power
roller. Roll in direction parallel to centerline of road. For areas inaccessible
to roller, compact using tampers or compactors.
For each lift, roll area to be compacted, without interruption, a
minimum of 8 complete coverage passes.
When thoroughly compacted, untreated permeable base course
shall conform to shape and dimension indicated in the contract
documents. Limit surface deviations of finished areas to not more than ½
inch above or below theoretical grade.
After rolling final lift, spread filler in a thin layer, not exceeding 30
pounds of filler per square yard of coarse aggregate surface area. Filler
shall be sufficiently dry to choke surface voids without caking or bridging.
Sprinkle surface with water and roll with two complete coverage passes.
Scatter excess filler by light brooming.
Apply primer on filler surface in accordance with Section 420 –
Primer for Untreated Permeable Base Course within 4 hours after roller
compaction.
Use sufficient filler and water to keep edges of untreated permeable
base course consolidated and compacted.
(E)
Protection of Untreated Permeable Base Course. Keep traffic off
untreated permeable base course, except for construction equipment
directly connected with primer operation.
343
Prevent foreign-material contamination that would reduce free
draining properties of untreated permeable base course. If contaminant or
filler, or both settle below surface voids, remove and reconstruct full depth of
untreated permeable base course at no increase in contract price or
contract time.
304.08 Measurement. Untreated permeable base course will be paid on a
lump sum basis. Measurement for payment will not apply.
304.09 Payment. The Engineer will pay for the accepted untreated permeable
base course on a contract lump sum basis. Payment will be full compensation
for the work prescribed in this section and the contract documents.
The Engineer will pay for the following pay item when included in the
proposal schedule:
Pay Item
Pay Unit
Untreated Permeable Base Course
Lump Sum
The Engineer will not pay for permeable separator, filler, and primer for
untreated permeable base course separately and will consider the cost for those
items as included in the contract price for the untreated permeable base course
contract pay item. The cost is for the work prescribed in this section, Section 313
– Permeable Separator, Section 420 – Primer for Untreated Permeable Base
Course, and the contract documents.
END OF SECTION 306
344
SECTION 624 - WATER SYSTEM
624.01 Description. This section describes constructing water systems and
appurtenances.
The terms "County Water Works System" or "Board of Water Supply
(BWS)" will be interchangeable and mean organization of respective County.
Use appropriate County Water Works System requirements for items of
work or materials required, but not specifically covered by contract documents.
624.02 Materials.
Aggregate for Untreated Base
703.06
Structure Backfill Material
703.20
Trench Backfill Material
703.21
Concrete Brick
704.02
Asphalt
705.06(C)
Concrete Cylinder Pipe
706.18
Ductile Iron Pipe, Fittings and Special Castings for Water System
707.01(B)
Copper Service Pipe and Appurtenances
707.11
Reinforcing Steel
709.01
Frames, Grates, Covers and Ladder Rungs
712.07
Pipe Collar for Valve Box
712.22
Precast Concrete Meter and Valve Boxes and Covers
712.23
Valves and Appurtenances
712.24
Fire Hydrants and Appurtenances
712.26
Cullet Materials for Utility Structures
717.03
RCA for Utility Structures
719.03
RAP for Utility Structures
720.03
345
Use Class B concrete conforming to Section 601 – Structural Concrete for
reaction beams, reaction test blocks, and jackets.
Inspect and test pipes, fittings, special castings, gate valves and butterfly
valves. Furnish two copies of manufacturer's certificate of test for pipes, fittings,
special castings and valves in accordance with Subsection 106.04 - Material
Sample.
624.03 Construction.
(A) General. Arrange work so no interruption in water service or damage
to existing water system and appurtenances occurs. Repair damages
made to existing water system and appurtenances at no increase in
contract price or contract time.
Locations of existing water system and appurtenances shown in
contract documents are approximate. If the Engineer requires changes in
alignment, grade or location due to unforeseen conflict with proposed
highway project, the Engineer may be responsible for such alterations and
cost.
Maintain access for Fire Department to existing fire hydrants within
project site. Install relocated fire hydrants before removing existing fire
hydrants.
Notify County Water Works System in writing at least one week
before commencement of work on water system.
Arrange with County Water Works System to cut off unused water
mains and service laterals, meter boxes, and other appurtenances before
commencement of clearing, grubbing, and grading operations. Excavate
for cut off work.
If corporation stop tapping into new main is larger than that allowed
by County Water Works System, install double hub fitting with boss tapped
for appropriate size corporation stop.
Invert grades of water mains and service laterals shall provide the
following minimum cover requirements from top of pipe to finish grades:
(1) Pavement areas: Minimum three feet, sleeve or concrete jacket
for six-inch or larger water mains.
(2) Under ditches: Minimum two feet, one foot, if paved.
346
(3) All other areas: Minimum three-foot cover.
(4) Highway utility encroachment committee may reduce the threefoot minimum clearance specified above to two feet if ground
conditions are ascertained to be rocky material, provided utility lines
do not encroach into the pavement structure.
(5) Minimum cover of utility service lines under sidewalk areas and
areas adjacent to the right-of-way (outside of shoulder and
pavement areas) shall be one-foot six inches.
Comply with requirements for the Occupational Safety and Health
Administration 29 CFR Parts 1910.146, Permit-Required Confined Spaces
for General Industry and Hawaii Occupational Safety and Health (HIOSH)
Confined Space Standard #12-104-1.
(B) Trench Excavation.
(1) General. Pile excavated material next to trench, or haul and
store to site acceptable to the Engineer. Maintain access to existing
driveways, fire hydrants, meters, vehicular traffic and pedestrian
walkways.
In fill areas, compact fill to subbase or to elevation 4 feet
above top of pipe barrel, whichever is less, before excavating
trench.
Expose existing mains by hand to verify their locations and
depths.
Excavate trenches in accordance with Section 204 –
Excavation and Backfill for Miscellaneous Facilities, and as
modified below.
For removal of existing water system and appurtenances,
provide trenches of sufficient size and depth to permit their removal
without damage. Carefully remove materials to be salvaged.
Replace materials damaged by the Contractor at no increase in
contract price or contract time.
Do not open trench more than 750 feet ahead of installed
and tested pipe. Do not construct trench with jumps or spaces
unless acceptable to the Engineer. Maintain excavation during
installation of water systems and placing of backfill.
347
Construct trench widths for various size pipes not encased in
concrete in accordance with Table 624.03-1 – Trench Widths for
Water System.
TABLE 624.03-1 – TRENCH WIDTHS FOR WATER SYSTEM
Diameter of Pipe Inches
Width of Trench
Inches
42
66
36
54
30
48
24
42
20
36
16
30
12
24
8
24
6
24
4
24
Below 4
12
Increases in widths to those specified in Table 624.03-1 –
Trench Widths for Water System may be made at no increase in
contract price or contract time.
For water mains encased in concrete, provide trench width
of concrete jacket plus 20 inches. If no forms are specified for
jacket, provide a trench width equal to width of concrete jacket. Use
depth of trench as bottom of concrete jacket.
Excavate trenches to a depth of six inches below invert
grade shown in contract documents, except as noted above for
concrete encased mains. The Engineer reserves the right to
eliminate six inches of excavation below invert grade and the right
to raise or lower invert grade, or to change alignment.
Correct trenches over-excavated below specified grade with
trench backfill material, compacted, at no increase in contract price
or contract time.
(2) Bell Holes. Enlarge bell holes at pipe joints to provide room for
completing joints.
(3) Reaction Blocks. Excavate to place reaction and test blocks.
(4) Removal of Mud and Other Unsuitable Material from Trench
Bottom. If soft, spongy, or other unsuitable material is encountered
at specified depths, remove material under pipe to maximum depth
348
of 30 inches below invert grade of pipe. Backfill space to 6 inches
below invert grade of pipe with untreated base. Use untreated base
with maximum aggregate size of 1-1/2 inches. Compact untreated
base until relative compaction is not less than 95 percent.
(5) Sheathing. Properly sheath and brace excavation to provide
secure excavation. Remove sheathing and bracing before
completing backfill. When sheathing is necessary, widen trench
beyond those widths specified in Subsection 624.03(B)(1) General.
(6) Dewatering. Keep trenches free from water while installing and
testing pipe and backfilling trench. Comply with NPDES
requirements and other applicable regulations. Obtain NPDES
construction dewatering permit for discharge of uncontaminated
ground water.
(7) Service Laterals and Service Connections and Meter Boxes.
Excavate and backfill in accordance with Section 204 – Excavation
and Backfill for Miscellaneous Facilities.
(8) Use of Explosives. The use of explosives is not permitted, in
accordance with Subsection 104.10 – Use of Explosives.
(9) Connections or Adjustments of Water Mains. If connections
to, or adjustments of existing water mains are required, perform
necessary excavation, placing of untreated base, and backfilling.
Before trenching for new main, expose existing main by
hand to detect actual location and grade for connection. Excavate
trench for exposing existing main to length, width, and depth
ordered by the Engineer.
Provide materials, excavate, backfill and do work required to
connect new or relocated meters to house services.
(C) Trench Backfill.
(1) General. Do not use adobe, clay or material of similar nature for
backfill. When removal of unsuitable excavated materials creates
shortage of backfill material, furnish suitable material. Material from
roadway or other excavation may be used.
(2) Preparation of Trench Bottom. After excavating trench to
proper depth below invert grade of pipe, backfill trench bottom to
required invert grade of trench with trench backfill material.
349
(3) Backfilling. Upon completion of testing of mains and
appurtenances, conform to following:
(a) For mains 12 inches and smaller, copper pipes, service
laterals, services connections and appurtenances, backfill
trench with Trench Backfill A material to 6 inches above top
of pipe, except as specified in subparagraph (c) below.
(b) For mains 16 inches and larger, place Trench Backfill A
material to 12 inches above top of pipe. Use maximum lift of
six inches.
(c) For pipe inverts below the 4-foot elevation, County datum
or in areas where the ground is continuously wet, use gravel
material conforming to AASHTO M 43, Size Number 67,
encapsulated in permeable separator, to minimum 12 inches
above top of pipe or to 12 inches above water level,
whichever is higher. Use maximum lift of six inches.
(d) Backfill remainder of trench with trench backfill material,
conforming to Subsection 703.21 – Trench Backfill Material.
(e) Place Trench Backfill A and B materials, and Structural
Backfill B material in layers not exceeding six inches in loose
thickness. Compact each layer to not less than 95 percent
relative compaction conforming to Subsection 203.03(C)(2)
Relative Compaction Test.
Upon completion of disinfection work, remove risers. Backfill
these areas with trench backfill material to not less than 95 percent
relative compaction.
(D) Laying Pipe. Inspect and test pipes and appurtenances before
installation. Mark circumference of spigot ends of pipe showing depth of
bell before installation.
Lay each pipe so barrel of pipe has bearing along its laying length
with bell end properly set to grade and alignment. Center spigot end of
pipe and embed firmly against bell end of pipe previously laid with uniform
clearance around bell. Hold pipe firmly in place by proper blocking on
each side of pipe. Do not lay pipe on blocks.
For cathodic protected pipe, handle pipe and appurtenances with
slings cushioned along areas in contact with pipe and appurtenances to
protect pipe coating.
350
Do not use springing or buckling of pipe lengths as means of fitting
them into place between installed pipe or special castings. Clean and
scrape pipes and appurtenances of foreign matter and protuberances.
Keep pipes and appurtenances clean until assembly of joint is completed.
If water, mud, or other foreign matter enter joints before assembly
of joint, and after installation of pipes or appurtenances, open joints
affected and clean joints before replacing and resetting pipes or
appurtenances.
Keep trench and pipe free of water. If water enters pipe, clean inner
portion of pipe before continuing with pipe installation.
Cold cutting with cold chisel and hammer will be allowed for 12-inch
and smaller cast iron pipes. Trim cut edges to be even and free from
projections.
Pipes 16 inch and larger shall be machine cut.
If installation of sleeves is necessary in pipelines, contact space
between ends of adjoining pipes by welding in place not less than four
filler pieces of same material as pipe. Use filler pieces 4 inches wide, of
suitable length, and equally spaced around circumference of pipe.
When pipe laying is stopped, close openings tightly with cast iron
removable plugs held securely in place.
Do not use pipes and appurtenances for water mains for other
purposes before installation.
(E) Gate Valves. Inspect valves to ensure their proper working order
before installation. If valves under pressure tests show leakage, stop
leaks. Use proper, standardized tools for operating valves. Install proper
size corporation stops on sides of valves as specified. When backfilling
valves, remove and replace corporation stops with brass plugs. Support
valves with blocks as specified. After completing manhole, or before
constructing valve boxes, clean valve of rust and foreign matter. Paint
valve with one coat of corrosion preventive paint acceptable to the
Engineer.
(F) Joints for Ductile Iron Pipe and Appurtenances.
(1) Mechanical Joints. Clean bell and spigot end of pipe and
rubber gasket before assembly. Place gland, followed by gasket,
over spigot end of pipe that is inserted into bell. Face small side of
351
gasket and lip side of gland towards bell. Push gasket into position
so that gasket seats evenly in bell as gland is moved against face
of gasket.
Dip threaded ends of bolts in fuel oil for lubrication before
assembly.
Insert bolts with threaded ends on gland side. Screw nuts by
hand and make nuts hand-tight in pairs (180 degrees apart).
Tighten bolts alternately (180 degrees apart) to desired tension with
ratchet wrench acceptable to the Engineer, beginning at bottom,
then top and so on. Conform normal range of bolt torques for
standard cast iron bolts in joint to Table 624.03-2 – Bolt Torques.
TABLE 624.03-2 – BOLT TORQUES
Bolt Size,
Range of Torque,
Inches
Foot - Pounds
5/8
40 - 60
3/4
60 - 90
1
70 - 100
1-1/4
90 - 120
Provide uniform distance around pipe between face of bell
and face of gland. After completion of joint, paint bolts with one coat
of asphalt paint.
(2) Slip Joint. Wipe gasket seat in socket of pipe and gasket with
cloth. Place gasket in socket with large, round end entering first.
Spring gasket into gasket seat so that groove fits over bead in seat.
Apply thin film of non-toxic lubricant, as supplied by
manufacturer, to inner diameter of gasket to facilitate insertion of
pipe. Apply thin film of lubricant to outer portion of plain end of pipe
for about 1 inch back from end.
Construct joint by exerting sufficient force on entering pipe to
move its plain end past gasket until pipe makes contact with base
of socket.
When cutting pipes in field, taper outer portion of cut end
approximately 1/8 inch at angle of 30 degrees to centerline of pipe
with coarse file or portable grinder.
(3) Flanged Ends Joint. Provide flange with face true and free of
projection. Clean face of flange of rust and foreign matter. Use full
face gaskets. Cut gaskets carefully to fit flanges and bolt holes.
352
Bring up flanges to true alignment and fit flanges with uniform
tension on bolts. Tighten bolts specified for mechanical joints. Paint
bolt threads with graphite before tightening.
(G) Pipes, Service Laterals and Service Connections, Including
Appurtenances.
(1) General. Service Lateral is that portion of installation from water
main up to and including stopcock end of lateral. Service
Connection is that portion of installation from stopcock end of
service lateral up to and including stop cock at meter box.
Appurtenances used with Pipes, Service Laterals and
Service Connections means fittings, corporation stops, valves,
bushings, and stop cocks that will be installed in service lateral and
service connections.
(2) Installation. Install service laterals and service connections at
specified locations and of sizes and types specified.
Conform to following procedure for solder joints:
(a) Cut pipe or tube to desired length with tube cutter or fine
hacksaw (32-tooth blade). Remove burrs with file or scraper.
(b) Clean outer portion of tube end that fits into solder cup of
fitting with sandcloth or sandpaper. Remove dark spots.
(c) Before soldering, ensure pipe end section is circular in
shape and not deformed. Use shaping/sizing tools on noncircular sections to provide proper connection.
(d) Clean solder cup of fittings carefully with wire brush,
sandcloth, or sandpaper. Remove dark spots.
(e) Use no-lead flux acceptable to the Engineer. Brush light,
even coating of flux onto outside of tube and half way into
inside of fitting. Do not use acid or zinc chloride.
(f) Insert tube into fittings as far as tube will go. Turn tube
back and forth few times to distribute flux evenly. Do not
wipe joints before inserting into place.
(g) Heat fitting uniformly with torch until solder melts on
contact with heated fitting. Remove flame from joint to be
soldered. Using only solders acceptable to the Engineer,
353
feed solder to joint at one or two points. Do not feed solder
around full circumference of tube. When ring of solder
appears around tube at fitting, stop solder feeding and wipe
excess off with cloth.
(h) For connections to tubes of 1-1/4 inch diameter and
larger, move fitting on tube or tap with tool handle or mallet
as solder is fed to break surface tension and ensure even
distribution of solder.
(i) Conform to County Water System Standards for corrosion
control requirements for copper services.
(3) Pipe Sleeves Through Retaining Walls. When constructing
cement rubble masonry walls or concrete retaining walls with later
installation of service connections through retaining walls, insert 2inch minimum diameter pipe sleeves at locations indicated in
contract documents.
(H) Fire Hydrants. Install fire hydrant and appurtenant pipe fittings and
valves as indicated in contract documents. Install fire hydrants with 4-1/2
inch steamer nozzle faced no more than 15 degrees to left or right of line
running from center of hydrant and perpendicular to street curb. Install fire
hydrants with barrels vertical. After checking hydrant for alignment and
grade, wedge barrel tightly against side of trench. Wedges may be
removed after concrete anchor block placed at bottom elbow has set.
Place concrete thrust block around bottom elbow to at least 12
inches above invert of elbow. Do not disturb concrete thrust block for
minimum of three days, or as ordered by the Engineer.
Use standard tools to operate fire hydrants.
If there is no standard curbing, protect fire hydrants with installation
of curb guards.
Before final inspection, clean fire hydrants of oil, grease, dirt or
other foreign matter. Paint fire hydrant in accordance with Subsection
712.26 – Fire Hydrants and Appurtenances.
(I) Concrete Reaction and Test Blocks, Concrete Jacket, and
Reaction Beams. If pipeline appurtenances are subject to unbalanced
thrust, brace them properly with plain or reinforced concrete reaction
blocks.
354
For testing purposes, provide reinforced concrete blocks in
accordance with County Water Works System Standards.
Cure concrete reaction and test blocks, concrete jackets, and
reaction beams for seven days before applying pressure in pipes.
Due to various types of vertical bends and surrounding ground
conditions, design of reaction blocks will vary. Costs for reaction block
redesign due to unauthorized excavation shall be at no increase in
contract price or contract time.
Install reinforced concrete jackets around ductile iron pipe as
specified in contract documents.
(J) Testing. Pipes and appurtenances are subject to pressure tests in
presence of the Engineer.
Whenever any section can be isolated as unit, perform separate
test on each section of pipeline with its appurtenances. If valves are
available at each end of section, perform test between valves. If valves
are not available, install necessary plugs or caps, properly braced to
withstand required test pressure. When section of pipeline is ready for
testing, tap test holes into pipe and connect test holes to test pump with
suitable piping. Between tap and pump, install stop cock. Between stop
cock and tap, install pressure gage furnished by County Water Works
System.
Fill section of pipeline to be tested completely with water. Ensure
that there are no air pockets. Open stopcock and raise hydrostatic
pressure to required pressure in accordance with Table 624.03-3 – Test
Pressure.
TABLE 624.03-3 – TEST PRESSURE
Class of Pipe
Test Pressure
150
150 psi
250
250 psi
above 250
50 psi above static pressure of
installed system
Shut stopcock and observe pressure gage for 30 minutes. For
acceptance, pressure shall not drop more than 10 pounds per square
inch, during this period.
The Engineer may require tests to cover sections or combination of
sections, and may require additional tests.
355
Provide equipment and material necessary for tests. After stopping
visible leaks and completing tests, install brass plugs in holes made for
testing purposes.
(K) Connections to or Adjusting of Existing Mains. Notify the Engineer
in writing before proceeding with connections to, or adjusting of existing
mains. Deliver this notice three working days before commencing with this
work.
Furnish materials required for work, and complete necessary
excavation.
Provide concrete reaction blocks and manholes, and complete
backfill and other incidental items of work.
Do not operate valves or hydrants unless authorized by the
Engineer. County Water Works System will operate valves 16 inches and
larger.
Provide material, excavate, backfill and connect new or relocated
meters to house services.
(L) Disinfection. Flush and disinfect water mains, service laterals, and
appurtenances before acceptance. Notify the Engineer and County Water
Works System 72 hours before time for disinfection. Provide connections
for disinfection. Properly dispose water used in disinfecting and flushing in
accordance with applicable Department of Health and NPDES
requirements.
Provide temporary cleanouts at locations indicated in contract
documents to ease disinfecting of water mains. After disinfecting mains
and receiving certification for disinfecting, remove temporary cleanouts.
Provide brass plugs to replace corporation stops.
(M) Meter Boxes and Cast Iron Frames and Covers.
(1) General. Construct meter boxes and cast iron frames and
covers.
(2) Installation. Construct meter boxes of:
(a) Bricks set in full mortar beds in accordance with standard
brick construction.
(b) Precast concrete with necessary reinforcing steel.
356
Install meter boxes at locations indicated in contract
documents. Install cast iron frames and covers of proper size and
dimension in full mortar beds at each meter box. Paint cast iron
frames and covers with one coat of high grade asphaltum paint.
(N) Air Relief Valves and Appurtenances. Construct air relief valves and
appurtenances. Appurtenances include pipes, fittings, corporation stops,
unions and vertical check valves. Clean air relief valves of rust and foreign
matter. Paint air relief valves with one coat of corrosion preventive paint
acceptable to the Engineer.
(O) Water Supply for Construction. County Water Works System will
measure quantity of water used for construction. County Water Works
System will provide and disconnect meter. Arrange with County Water
Works System and pay costs for such installations and disconnections.
County Water Works System will furnish invoices for cost of installation
and disconnection of meters. Pay for cost of replacements or repairs
resulting from damage to meter, hydrant and other property used.
Provide water supply equipment and materials necessary to
provide adequate water supply for proper construction of water mains.
Equipment and materials may include temporary pipes and fittings,
pumping, and storage facilities.
(P) Maintaining Existing Water System. Maintain existing water system
in service during construction period, and until new water system is placed
in service and existing services are transferred to new system.
Immediately notify the Engineer and County Water Works System
of damages to existing system. County Water Works System will do
necessary repairs. County Water Works System will bill the Contractor for
costs incurred in this work.
After installing new system or portions of new system, remove
existing meters and reconnect existing meters to new system. New
system includes its appurtenances, service laterals, service connections,
and boxes. For work ordered by State, and to be done by County Water
Works System personnel, County Water Works System will send invoices
directly to State. County Water Works System will not charge or pay cost
of this work to the Contractor.
(Q) Removing, Reinstalling or Returning Existing Pipe. Clean existing
pipe that is to be removed and reinstalled in new locations before
installing.
357
Existing pipe includes its appurtenances, fire hydrants, gate valves,
and manhole frames and covers. Paint manhole frames and covers with
one coat of high-grade asphaltum paint.
Clean and return existing pipe removed and not reinstalled to
County Water Works Storage Yard as ordered by the Engineer.
Assume responsibility for removing, reinstalling, or returning these
existing pipes. Pay for damages to materials during these operations.
(R) Abandoning Existing Pipe. If ordered, expose portions of abandoned
pipe. If top of pipe is less than 24 inches below finished grade, remove
and dispose existing pipe off right-of-way. If abandoning pipe in place,
plug ends of abandoned pipe with Class C concrete. Backfill in
accordance with Section 204 – Excavation and Backfill for Miscellaneous
Facilities.
(S) Corrosion Protection. Apply corrosion protection to pipes, valves and
fittings as specified in County Water System Standards. Use specified
materials and methods of application.
(T) Valve Markers. Install valve markers for establishing location of gate
valves and air relief valves.
Fill markers with concrete and set markers plumb in Class B
concrete footing. Paint pipe yellow. Paint top 4 inches of markers for air
relief valves red.
624.04 Measurement. Water system will be paid on a lump sum basis.
Measurement for payment will not apply.
624.05 Payment. The Engineer will pay for accepted water system on a contract
lump sum basis. Payment will be full compensation for work prescribed in this
section and contract documents.
The Engineer will pay the following pay item when included in proposal
schedule:
Pay Item
Pay Unit
Water Systems
Lump Sum
The Engineer will pay for:
(A) Excavation and backfill under Section 204 – Excavation and Backfill
for Miscellaneous Facilities.
358
(B) Concrete in reaction blocks, test blocks, jackets, and reaction beams
under Section 503 – Concrete Structures.
(C) Reinforcing steel under Section 602 – Reinforcing Steel.
END OF SECTION 624
359
SECTION 625 - SEWER SYSTEM
625.01 Description. This section describes constructing sewer systems and
appurtenances.
Terms "Sewage" or "Wastewater" and "Division of Sewers" or "Division of
Wastewater Management" (DWM) will be interchangeable depending on
respective County.
625.02 Materials.
Bed Course Materials for Crushed Rock Cradle
703.16
Structure Backfill Material
703.20
Trench Backfill Material
703.21
Joint Mortar for Pipe
705.02
Jointing Compound for Sewer Pipe
705.11
RCP for Sewer System
706.02(B)
Vitrified Clay Pipe (VCP) and Fittings for Sewer System
706.08
PVC for Sewer System
706.09
Cast Iron Pipe and Fittings for Sewer System
707.01(A)
Ductile Iron Pipe, Fittings and Special Castings for Water System
707.01(B)
Reinforcing Steel
709.01
Cullet Materials for Utility Structures
717.03
RCA for Utility Structures
719.03
RAP for Utility Structures
720.03
Conform concrete for sewer structures to Section 601 – Structural
Concrete. Use Class C concrete for non-reinforced concrete blocks, cradles, and
jackets. Use Class B concrete for reinforced concrete blocks, cradles, and
jackets.
Modify concrete in contact with sewage or sewage gases as follows:
360
(1) Incorporate water reducing admixture conforming to Subsection
711.03(B) – Admixture Acceptance.
(2) Use Type II portland cement or modified Type I portland cement
with maximum limit of 8 percent on tricalcium aluminate.
Use 2-inch square redwood, or 1-1/2 inch diameter PVC pipe, of
required length for markers for house connection reducers.
625.03 Construction
(A) Open Trench Excavation for Sewer Pipes. Excavate trenches in
accordance with Section 204 – Excavation and Backfill for Miscellaneous
Facilities and below:
(1)
Trench Widths. Construct trench widths in accordance with
Table 625.03-1 – Trench Widths for Sewer Pipes.
TABLE 625.03-1 - TRENCH WIDTHS FOR SEWER PIPES
Pipe Size - Inches
Trench Width – Inches
6
24
8
24
10
24
12
30
15
38
18
41
21
45
24
50
27
53
30
57
36
69
42
76
48
84
54
91
Increases in widths over those specified in Table 625.03-1 Trench Widths for Sewer Pipes may be made at no increase in
contract price or contract time.
If trench width is greater than that specified in Table 625.031 – Trench Widths for Sewer Pipes, and such condition results in
greater load of overburden than Department designed pipe for,
provide at no increase in contract price or contract time:
(a) Higher strength replacement pipe.
361
(b) Higher class of bedding.
Pile excavated material next to trench, or haul and store to
site acceptable to the Engineer. Obstructing movement of vehicular
traffic and pedestrian walkways will not be allowed. Maintain
access to existing driveways, fire hydrants, and meters.
For pipe
embankment:
installation
in
new
embankment,
construct
(a) To required height.
(b) For a distance on each side of pipe location not less than
five times diameter of pipe.
Excavate trench with sides as nearly vertical as permitted by
soil conditions. Shore trench in accordance with OSHA
requirements.
Excavating more than 300 feet ahead of installed pipe will
not be allowed. Trench left unfilled more than 300 feet behind
installed pipe will not be allowed.
(2)
Trench Depths. Excavate trench to depth in accordance
with contract documents. Follow OSHA requirements.
If trench excavation is deeper than specified in the contract
documents, bring trench to specified grade, at no increase in
contract price or contract time:
(a) With bed course material.
(b) Class C concrete placed with cradle.
If mud or other unsuitable material is encountered at
specified grade, excavate below specified grade to depth and width
ordered by the Engineer, and backfill with bed course material.
If contract documents specify concrete to bed pipe, consider
top of concrete as top of bedding. Bedding material includes one of
following:
(a) Concrete.
362
(b) Beach sand conforming to Subsection 703.01 – Fine
Aggregate for Concrete.
(c) No. 8 or No. 67 aggregate conforming to gradation
requirements of ASTM C 33.
(d) Native free-draining granular material having a minimum
sand equivalent of 30 or having a coefficient of permeability
greater than 0.001 centimeter per second.
(e) Other materials acceptable to the Engineer.
(3) Sheathing and Bracing.
(a) General. Provide and maintain sheathing and bracing
required to support excavation. Follow OSHA requirements.
(b) PVC Pipe. If timber sheeting is used below top of PVC
pipe, drive timber sheeting approximately 2 feet below
bottom of pipe. Leave timber sheeting in place about 1-1/2
feet above top of pipe.
(c) Movable Trench Sheeting, Trench Boxes or Shields.
If bottom of sheeting, box, or shield extends below top of
pipe, use movable trench supports only:
1. On shelf above pipe with pipe installed in narrow,
vertical-wall subditch.
2. If located at least 2-1/2 pipe diameters away from
flexible pipe.
unless means to reconsolidate bedding or side support
material disturbed by shoring removal is acceptable to
Engineer.
(4) Dewatering of Trenches. Keep drainage or seepage water
below level of subgrade:
(a) When installing pipe, cradles or jackets.
(b) During periods of construction work inspection.
(c) During leakage tests.
363
Consider subgrade as bottom of concrete blocks or
jacket. Keep trenches free of water while installing and
testing pipe and backfilling trench. Comply with NPDES
requirements and other applicable regulations. Obtain
NPDES construction dewatering permit for discharge of
uncontaminated ground water.
(B) Installation of Sewer Pipe.
(1) General. Lay pipe starting from lowest point with spigots facing
direction of flow. Fit and match pipe together to provide sewer true
to line and grade with smooth and uniform invert.
Do not use blocks and wedges to adjust pipe to proper line
and grade, except as required for jackets and cradles. Uniformly
support pipe for its entire length.
Close exposed ends of sewers with accepted temporary
covers at end of each work day. If water, mud or other foreign
matter enters joints after pipe installation, open, clean, and replace
affected joints.
Check pipes that become submerged in water during the
night each morning. Re-lay pipes that have floated from their proper
positions at no increase in contract price or contract time. Before
final inspection, visually inspect lines, and remove mud and other
foreign matter within sewer line.
Comply with requirements of Hawaii Occupational Safety
and Health (HIOSH) Confined Space Standard §12-67.2-2.
For sewer manhole, see Subsection 626.03(B)(2) - Sewer
Manholes.
(2) Vitrified Clay Pipe. Install vitrified clay pipe with compression
joints. Wipe or brush the pipe with lubricant or adhesive
recommended by pipe manufacturer on contact surfaces of joints.
Push spigot into bell until joint snaps into position.
Do not use poured or formed joints using cement, sulfur
compounds, bituminous materials, or other materials forming rigid
joint.
Use jointing compound recommended by pipe manufacturer
for joining 6-inch by 4-inch extra heavy cast iron or ductile iron
reducer to 6-inch vitrified clay sewer pipe and 4-inch house sewer.
364
(3) Cast Iron and Ductile Iron Pipe and Appurtenances.
Construct in accordance with Subsections 624.03(D) – Laying Pipe
and 624.03(F) – Joints for Ductile Iron Pipe and Appurtenances.
(4) Reinforced Concrete Pipe. Clean inside surface of concrete
bell and concrete spigot end, including groove, before making joint.
Lubricate rubber gasket and annular groove in spigot. Stretch and
place gasket uniformly in annular groove in spigot. Lubricate inside
bell surface 2 inches from end of pipe. Use soft vegetable soap
compound lubricant recommended by manufacturer.
Before assembling joint, place metal or wooden spacers
against shoulder of bell and provide proper space between abutting
ends of pipe.
Telescope and seat spigot into bell. Do not mortar joints,
inside or outside.
Insert thin metal feeler gage between bell and spigot. Check
position of rubber gasket around complete circumference of pipe. If
gasket is not in proper position;
(a) Withdraw pipe.
(b) Check gasket for cuts and damages.
(c) Re-lay pipe.
(d) Recheck gasket position.
Provide joint openings:
(a) Within tolerance recommended by manufacturer.
(b) Consistent with design of pipe.
(c) To not exceed 1/2 inch.
If joint opening exceeds any of above requirements,
withdraw pipe, correct defect, and re-lay pipe.
(5) PVC Pipe. Wipe clean and lubricate compression joints with
lubricant provided by manufacturer before inserting spigot end of
pipe into bell end.
365
Handle, load, unload, and store PVC pipe with care. Store
pipe and fittings under cover. Transport pipe and fittings in vehicle
with bed long enough to allow length of pipe to lie flat.
Place four inches of bedding material below pipe, plus
additional bedding material above the bottom of pipe equal to 0.4
times outside diameter of pipe. If laying pipe in rock excavation,
remove six inches of rock below pipe and place six inches of
bedding below pipe.
Cover pipe with minimum of 3 inches of accepted backfill
material within 24 hours after placing pipe in trench.
Bedding from bottom of pipe to 12 inches above pipe may be
compacted by jetting, provided applied water does not soften or
damage foundation material. Use 1-1/2 inch nozzle curved to
circumference of installed pipe with sufficient length to reach invert
of pipe. Conduct compaction along entire length of pipe on
alternate sides with each side compacted four times. Provide
additional material and compaction if settlement is greater than 1/6
diameter of pipe. Maintain required grades. Compact backfill from
12 inches above pipe to finish surface in accordance with Section
204 – Excavation and Backfill for Miscellaneous Facilities.
Provide special watertight manhole couplings for manhole
connections. Cast couplings directly into cast-in-place manholes, or
grout couplings into precast concrete manholes with non-shrink or
expansion-type grout.
(6) Leakage Tests.
(a) General. Test sewers and sewer manholes for leakage in
presence of the Engineer. Provide equipment and material
necessary for tests including water and labor. Perform
leakage test with results acceptable to the Engineer before
placing backfill, concrete cradles, concrete jackets, or
permanent resurfacing.
(b) Force Mains. Test force mains in accordance with
Subsection 624.03(J) – Testing.
(c) Gravity Lines. Do not perform exfiltration leakage test if
difference in elevation between inverts of adjacent manholes
exceeds 10 feet.
366
If ground water is above top of pipe, perform leakage
(infiltration) tests as follows:
(1) After laying pipe and completing connections to
manholes, backfill pipe trench to prevent floating of
pipe.
(2) Close end of sewer at upper structure to prevent
entrance of water. Stop pumping of ground water for
at least three days. Test the test portion for infiltration.
(3) Use maximum quantity of infiltration of 200 gallons
per day per inch of inside diameter per mile of pipe.
(4) Reduce infiltration over limit specified above to
within permissible limit before sewer is acceptable the
Engineer. Repair visible leaks, despite limits of
leakage tests.
If ground water is below top of pipe laid, perform
leakage (exfiltration) tests as follows:
(1) Test each portion of sewer between successive
manholes by closing the inlet of the lower manhole
and and closing the inlet of upper manhole with
stoppers. Fill pipe and upper manhole with water:
(a) At least 4 feet above invert of upper
manhole.
(b) Or, not less than 1 foot above high end of
highest house connection on test portion.
(2) If construction of manhole is delayed, use barrel
on bank to provide necessary pressure required for
testing.
(3) Keep water present in trench below level of
subgrade of sewer during test, and during patching or
repairing required by test.
(4) Use maximum quantity of exfiltration 200 gallons
per day per inch of inside diameter per mile of pipe.
(5) Reduce exfiltration over limit specified above to
within permissible limit before acceptance by the
367
Engineer. Repair visible leaks, despite limits of
leakage tests.
(d) Low Pressure Air Test
(1) Clean pipe to be tested.
(2) Plug pipe outlets with test plugs. Securely brace
each plug.
(3) Add air until internal pressure of line reaches
approximately 4 pounds per square inch. After
reaching this pressure, allow pressure to stabilize.
Pressure will normally drop as air temperature
stabilizes, usually taking two to five minutes
depending on pipe size. Reduce pressure to 3-1/2
pounds per square inch before starting test.
(4) Start test when pressure:
(a) Has stabilized.
(b). Is at or above starting test pressure of 31/2 pounds per square inch.
If pressure does not drop more than 1 pound
per square inch during test time, line has passed test.
(5) Ground water above pipe will reduce air loss. If
section of line under test shows significant infiltration,
perform infiltration test.
(6) Air test may be dangerous if line is prepared
improperly. Install and brace plugs to prevent
blowouts.
Provide pressurizing equipment with regulator
set at 10 pounds per square inch to avoid overpressurizing and damaging acceptable line. Do not
allow workers in manholes during testing.
368
TABLE 625.03-2 - MINIMUM AIR TEST TIME FOR VARIOUS PIPE SIZES
Nominal Pipe
T (Time)
Nominal Pipe
T (Time)
Size, Inches
minutes /100
Size, Inches
minutes /100 feet
feet
3
0.2
21
3.0
4
0.3
24
3.5
6
0.7
27
4.2
8
1.2
30
4.8
10
1.5
33
5.4
12
1.8
36
6.0
15
2.1
39
6.6
18
2.4
42
7.3
(7) Mandrel Test for Deflection of PVC Pipe.
Perform mandrel test 30 days after completing trench
backfill. In roadway areas, 30- day period begins after
installation and compaction of bedding, backfill and
subbase to within 2 feet of finished pavement grade.
Pull rigid nine-sled mandrel through pipe by
hand between adjacent manholes to measure for
obstructions such as deflections, joint offsets, and
lateral pipe intrusions. Use mandrel conforming to
ASTM D 3033 and ASTM D 3034. Furnish material,
equipment, and labor required for test, and perform
test in presence of the Engineer.
If mandrel fails to pass, pipe is considered
overdeflected. If pipe is not damaged, uncover and
reinstall pipe. Remove damaged pipe from work site.
Do not reround or use other methods or processes to
reduce or remedy overdeflections.
(8) Connections to Existing Sewers.
(a) General. Arrange with County Division of
Sewers for making connections to existing
sewers.
(b) Breaking into Existing Manholes.
Connect to existing manholes and channelize
inverts in presence of County Division of
Sewers inspector. In making connection, place
tight fitting false form on inside portion of
manhole. Remove materials falling inside
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existing sewer pipe. Pay for damages to
existing manhole and sewer pipe resulting from
this work. After completing connection, work on
required channelizing within existing manhole.
(c) Sewer Enclosed Within New Manhole. If
building new manhole over existing sewer
main, cut existing sewer line in presence of
County Division of Sewers inspector. Clear
new manhole of mud, debris, and standing
water before cutting existing sewer line.
(d) Saddle Wye. If required to install new
lateral from existing sewer main, provide
saddle wye tap-in in presence of County
Division of Sewers inspector.
(C) Trench Backfill. Do not place backfill until testing of pipe and
appurtenances is acceptable to the Engineer. After installing and testing
pipe, immediately backfill trench and around manhole. Backfill in
accordance with Section 204 – Excavation and Backfill for Miscellaneous
Facilities.
If using sheathing, fill and tamp cavities formed below invert grade
before proceeding with backfill of trench.
Place and tamp trench backfill material placed below horizontal
plane 12 inches above top of pipe by hand shoveling so that backfill
material is in contact with entire periphery of pipe. Use Trench Backfill A
material conforming to Subsection 703.21 – Trench Backfill Materials.
Backfill remainder of trench with Structural Backfill B or Trench
Backfill B material conforming to Subsection 703.20 – Structure Backfill
Material or 703.21 - Trench Backfill Materials.
For sewer pipes that are cradled, bring initial backfill up to top of
pipe, moisten, and tamp.
In lawns, gardens, and other cultivated areas, backfill upper 12
inches with planting soil or loam and tamp. Plant grass, reset plants and
shrubs, and irrigate area for seven days.
(D) Concrete Blocks. Provide concrete blocks next to each bell on both
pipes and fittings.
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(E) Concrete Cradle. Provide concrete cradles under entire length of pipe
as specified in contract documents. Before placing concrete, rest pipes
firmly on concrete blocks. Keyway or curing is not required. Provide
reinforcement as specified in contract documents.
(F) Crushed Rock Cradle. Provide crushed rock cradle under entire
length of pipe as specified in contract documents. Provide bed course
material in layers not exceeding 8 inches in loose thickness and compact.
(G) Concrete Jackets. Provide concrete jackets as specified in contract
documents. Use small concrete blocks to support pipes, and provide
reinforcement as specified in the contract documents. Cure reinforced
concrete jackets for five days. Plain concrete jackets do not require curing.
(H) House Sewer Connection. Arrange connections to cause least
inconvenience for sewer user.
(I) Removing or Abandoning Existing Sewer System. If requested by
the Engineer, expose portions of existing sewer pipe to be removed or
abandoned. Excavate in accordance with Subsection 625.03(A) – Open
Trench Excavation for Sewer Pipes.
If top of pipe is less than 24 inches below finished grade, and the
Engineer orders pipe removed, proceed with pipe removal work. The
Engineer will order exact position of cutting for pipe removal work. Plug
open ends of abandoned pipes with Class B concrete. Plug ends of
existing pipes to remain in use with vitrified clay cap.
Backfill open trench with accepted select material and tamp in
uniform horizontal layers not exceeding 8 inches in loose thickness. Use
backfill tampers to provide relative compaction of not less than 95 percent.
Clean and deliver salvaged materials as ordered by the Engineer.
625.04 Measurement. Sewer systems will be paid on a lump sum basis.
Measurement for payment will not apply.
625.05 Payment. The Engineer will pay for accepted sewer systems on a
contract lump sum basis. Payment will be full compensation the work prescribed
in this section and contract documents.
The Engineer will pay for following pay item when included in proposal
schedule:
Pay Item
Pay Unit
371
Sewer Systems
Lump Sum
The Engineer will pay for excavation and backfill for sewer pipes under
Section 204 – Excavation and Backfill for Miscellaneous Facilities.
The Engineer will not pay separately for concrete blocks, cutting and
plugging of abandoned sewers, concrete plugs for ends of abandoned sewers,
and vitrified clay caps at ends of existing sewers that will remain in use. Consider
cost for these items as included in sewer system contract pay items.
END OF SECTION 625
372
SECTION 703 - AGGREGATES
703.04 Aggregate for Untreated Permeable Base.
Use of recycled
materials shall not be permitted in the untreated permeable base. Aggregate for
untreated permeable base shall conform to the following:
(A)
Coarse Aggregate. Coarse aggregate shall consist of crushed
and screened basalt that is free of soft or disintegrated pieces, clay, dirt,
organics, and other deleterious substances.
Coarse aggregate shall conform to Table 703.04-1 – Aggregate
Test Requirements.
TABLE 703.04 – 1 – AGGREGATE TEST REQUIREMENTS
Test
Test Method
Requirement
Los Angeles Abrasion ASTM C 535 (Coarse Aggregate) 40 Percent
AASHTO T 96 (Filler)
Maximum
Grading
AASHTO T 27
Refer to Table
703.04-2
(B)
Filler. Filler material shall conform to Subsection 703.04(A) –
Coarse Aggregate, except grading shall conform to Table 703.04-2 –
Grading Requirements.
TABLE 703.04-2 - GRADING REQUIREMENTS
Screen
Coarse Aggregate
Filler Size 8
Size
Modified Size 4
(Percent Passing By
(Percent Passing By
Weight)
Weight)
2 inch
100
1-1/2 inch
75-100
1 inch
15-55
¾ inch
0-15
½ inch
100
3/8 inch
0-5
85-100
No. 4
10-30
No. 8
0-10
No.16
0-5
703.06
Aggregate for Untreated Base. Aggregate for untreated base
shall consist of crushed stone one of the following:
1. 100% virgin aggregate
2. a mixture of virgin aggregate and cullet
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3. a mixture of virgin aggregate and RAP
4. a mixture of virgin aggregate and RCA, or
5. a mixture of virgin aggregate, RAP and RCA.
The untreated base shall be free of organics, vegetable matter and other
deleterious substances. A maximum of 10% cullet, 50% RAP or 100% RCA by
dry weight of the mixture is permitted in the untreated base course. Use of more
than one type of recycled material shall not be allowed in a base course except a
three-way combination of virgin aggregate, RAP and RCA is permissible. The
requirements for cullet, RCA and RAP shall conform to 717.02 – Cullet Materials
for Roadways, 719.02 – RCA for Roadways, and 720.02 – RAP for Roadways,
respectively. (Neither reclaimed asphalt pavement (RAP) nor reclaimed concrete
pavement will be allowed for untreated base.)
Crushing of virgin aggregate shall be regulated so that at least 80 percent,
by weight, of material retained on the No. 4 sieve is crushed and has at least one
mechanically fractured face.
Aggregate for untreated base, in combination with binder material, if used,
shall conform to Table 703.06-1 – Untreated Base Test Requirements and Table
703.06-2 – Untreated Base Grading Requirements. The tabulated requirements
apply to the virgin aggregate when used alone and to the combined virgin
aggregate and recycled material when used as a blend.
TABLE 703.06-1 – UNTREATED BASE TEST REQUIREMENTS
Test
Test Method
Requirement
Los Angeles Abrasion
AASHTO T 96
40 Percent Maximum
Sand Equivalent
AASHTO T 176
35 Percent Minimum
Plasticity Index
AASHTO T 90
6 Percent Maximum
Grading
AASHTO T 27
Refer to Table 703.06-2
California Bearing Ratio
AASHTO T 193
80 percent minimum1
Note: 1) The CBR shall be at least 80 percent as measured on a sample
compacted at optimum moisture content and after 4 days of soaking. The sample
shall be subjected to a surcharge equal to 10 lbs during soaking and penetration.
The optimum moisture content and maximum dry unit weight shall be determined
in accordance with AASHTO T 180 Method D, prepared using 5 layers at 56
blows.
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TABLE 703.06-2 – UNTREATED BASE GRADING REQUIREMENTS
Percent Passing by Weight
Sieve Size
2-1/2 inch
1-1/2 inch
3/4 inch
Maximum
Maximum
Maximum
Nominal
Nominal
Nominal
3 inch
2-1/2 inch
2 inch
1-1/2 inch
1 inch
¾ inch
No.4
No. 200
100
90 - 100
65 - 90
45 - 70
25 - 45
3-9
100
90 - 100
50 - 90
25 - 50
3-9
100
90 - 100
35 - 55
3-9
Unless otherwise indicated in the contract documents, 1-1/2 inch
maximum nominal size aggregate shall be furnished.
Material used as foundation for corrugated metal pipe culvert shall be
tested in accordance with Hawaii Test Method HDOT TM 4 and shall have field
resistivity and pH value that provide minimum 50-year service life for gage being
installed. Material used as backfill against aluminum pipe shall have field
resistivity of more than 500 ohm-centimeter and pH value between 5.5 and 9.0,
using same test procedure. The use of RCA shall not be permitted within 10 feet
of any aluminum or metal pipe or structure.
703.17
Aggregate for Subbase. Aggregate for subbase shall consist of
one of the following:
1. 100% virgin aggregate (such as gravel, stone, basalt, or coral, or
combination thereof)
2. a mixture of virgin aggregate and cullet
3. a mixture of virgin aggregate and RAP
4. a mixture of virgin aggregate and RCA, or
5. a mixture of virgin aggregate, RAP and RCA.
The aggregate for subbase shall be free of organics, overburden,
vegetable matter, and other deleterious substances. A maximum of 25% cullet,
50% RAP or 100% RCA by dry weight of mixture is permitted in the subbase.
RCA shall not be used in the top 6 inches of the subbase when the subbase lies
below a permeable base layer.
Use of more than one type of recycled material shall not be allowed in a
subbase except a three-way combination of virgin aggregate, RAP and RCA is
permissible. The requirements for cullet, RCA and RAP shall conform to 717.02 –
Cullet Materials for Roadways, 719.02 – RCA for Roadways, and 720.02 – RAP
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for Roadways, respectively. (Neither reclaimed asphalt pavement (RAP) nor
reclaimed concrete pavement will be allowed for untreated base.)
The tabulated requirements apply to the virgin aggregate when used alone
and to the combined virgin aggregate and recycled material when used as a
blend. When tested in accordance with AASHTO T 27, subbase shall conform to
Table 703.17-1 – Subbase Grading Requirements.
TABLE 703.17-1 – SUBBASE GRADING REQUIREMENTS
Percent Passing by Weight
Sieve Size
Subbase Material
Subbase Material
Placed in Top 6
Placed Below Top 6
Inches
Inches
6 inch
100
2-1/2 inch
100
No. 4
20 - 60
20 - 60
No. 200
0 - 15
0 - 15
When tested in accordance with AASHTO T 176, SE value shall not be
less than 25. A minimum SE of 20 shall be provided when material passing No. 4
sieve is entirely crushed coral limestone.
When tested in accordance with AASHTO T 89 and AASHTO T 90,
subbase shall conform to Table 703.17-2 – Subbase Plasticity Index.
TABLE 703.17-2 – SUBBASE PLASTICITY INDEX
Percent Passing No. 200 Sieve
Plasticity Index
0-9
15 Percent Maximum
10 - 15
10 Percent Maximum
When tested in accordance with AASHTO T 193, the CBR shall be at least
60 percent as measured on a sample compacted at optimum moisture content
and after 4 days of soaking. The sample shall be subjected to a surcharge equal
to 10 lbs during soaking and penetration. The optimum moisture content and
maximum dry unit weight shall be determined in accordance with AASHTO T 180
Method D, prepared using 5 layers at 56 blows.
The use of RCA shall not be permitted within 10 feet of any aluminum or
metal pipe or structure.
703.20
Structure Backfill Material.
consist of one of the following:
Structure backfill material shall
1. 100% virgin aggregate
2. a mixture of virgin aggregate and cullet
3. a mixture of virgin aggregate and RAP
4. a mixture of virgin aggregate and RCA, or
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5. a mixture of virgin aggregate, RAP and RCA.
Structure backfill shall be free of organics, vegetable matter and other
deleterious substance. A maximum of 25% cullet, 50% RAP or 100% RCA by
dry weight is permitted in the structure backfill. Use of more than one type of
recycled material shall not be allowed in the structure backfill except a three-way
combination of virgin aggregate, RAP and RCA is permissible. The requirements
for cullet, RCA and RAP shall conform to 717.02 –
Cullet
Materials
for
Roadways, 719.02 – RCA for Roadways, and 720.02 – RAP for Roadways,
respectively.
The tabulated requirements apply to the virgin aggregate when used alone
and to the combined virgin aggregate and recycled material when used as a
blend. Structure backfill shall conform to the grading requirements in Table
703.20-1 - Structure backfill grading requirements and other requirements of this
subsection
TABLE 703.20-1 – STRUCTURE BACKFILL GRADING REQUIREMENTS
Percent Passing by Weight
Sieve Size
Structure Backfill
Structure Backfill
Material A
Material B
3 inch
No. 4
No. 200
100
20 – 75
0 – 15
100
20 – 100
-
SE shall be tested in accordance with AASHTO T 176. Structural backfill
material A shall have minimum SE of 20. Structural backfill material B shall have
SE equal to or greater than SE of surrounding soil in area to be backfilled.
The use of RCA shall not be permitted within 10 feet of any aluminum or
metal pipe or structure.
703.21
Trench Backfill Material. Trench backfill material shall consist of
one of the following:
1. 100% virgin aggregate
2. a mixture of virgin aggregate and cullet
3. a mixture of virgin aggregate and RAP
4. a mixture of virgin aggregate and RCA, or
5. a mixture of virgin aggregate, RAP and RCA.
Two types of trench backfills are defined: (1) ―non-critical‖ trench backfill
refers to the portion of a trench backfill that is more than 5 feet below the road
surface or the entire portion of a trench backfill that is in an unpaved area; and
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(2) ―critical‖ trench backfill refers to the portion of a trench backfill that is 5 feet or
less below the road surface and that is subject to surcharge, and the entire
portion of a trench backfill that is in an embankment. For non-critical trench
backfill, a maximum of 100% cullet, 100% RAP or 100% RCA by dry weight is
permitted for use. For critical trench backfill, a maximum of 25% cullet, 50% RAP
or 100% RCA by dry weight is permitted for use.
Use of more than one type of recycled material shall not be allowed in the
trench backfill except a three-way combination of virgin aggregate, RAP and
RCA is permissible. The requirements for cullet, RCA and RAP shall conform to
717.02 – Cullet Materials for Roadways, 719.02 – RCA for Roadways, and
720.02 – RAP for Roadways, respectively. Coarse aggregate material shall be
used for trenches where invert of pipe is in swampy areas or under water.
Coarse aggregate material shall conform to ASTM C 33, size number 67, and
shall be completely encapsulated with geotextile conforming to Subsection
716.03 – Geotextiles for Underdrain Applications. Trench backfill material shall
be free of trash, roots, organic matter, and other deleterious materials.
The tabulated requirements apply to the virgin aggregate when used alone
and to the combined virgin aggregate and recycled material when used as a
blend. The requirements for trench backfill shall conform to Table 703.21-1 –
Trench Backfill Grading Requirements and the other requirements of this
subsection.
TABLE 703.21-1 – TRENCH BACKFILL GRADING REQUIREMENTS
Percent Passing by Weight
Sieve Size
Trench Backfill
Trench Backfill
Material A
Material B
(Critical)
(Non-critical)
3 inch
100
1 inch
100
No. 4
75 – 100
20 – 100
No. 200
0-15
Trench backfill material placed against corrugated metal pipe culvert shall
be tested in accordance with Hawaii Test Method HDOT TM 4 and shall have
field resistivity and pH values that provide a minimum 50-year service life for the
gage being installed. Trench backfill material placed against aluminum pipe shall
have a field resistivity of more than 500 ohm-centimeter and a pH value between
5.5 and 9.0, using the same test procedure.
The use of RCA shall not be
permitted within 10 feet of any aluminum or metal pipe or structure.
(A)
Trench Backfill Material A. Trench backfill material shall be
sandy material classified as SW, SP, SM, or SW-SM, or SP-SM in
accordance with ASTM D 2487. SE value of trench backfill A, determined
in accordance with AASTHO T 176, shall not be less than 20 and not less
378
than SE value of surrounding soil in trench to be backfilled. Reclaimed
asphalt pavement (RAP) shall not be used for trench backfill material A.
(B)
Trench Backfill Material B. SE value of trench backfill B,
determined in accordance with AASHTO T 176, shall be not less than SE
value of surrounding soil in trench to be backfilled.
703.23
Aggregate for Dressing of Shoulders. Aggregate for dressing of
shoulders shall conform to Subsection 703.17 – Aggregates for Subbase, except
that 100 percent of material shall pass 1-1/2 inch sieve.
703.24
Granular Material for Embankment. Granular material for
embankment shall consist of one of the following:
1. 100% virgin aggregate (such as gravel, stone, lava rock, coral, or cinders,
or combination thereof)
2. a mixture of virgin aggregate and cullet
3. a mixture of virgin aggregate and RAP
4. a mixture of virgin aggregate and RCA, or
5. a mixture of virgin aggregate, RAP and RCA.
A maximum of 25% cullet, 50% RAP or 100% RCA by dry weight is
permitted in the embankment fill. Use of more than one type of recycled material
shall not be allowed in the granular material for embankment except a three-way
combination of virgin aggregate, RAP and RCA is permissible. Granular material
for embankment shall be free of organics, overburden, vegetable matter, and
other deleterious substances. Pit run material is acceptable. The requirements
for cullet, RCA and RAP shall conform to 717.02 – Cullet Materials for
Roadways, 719.02 – RCA for Roadways, and 720.02 – RAP for Roadways,
respectively.
The tabulated requirements apply to the virgin aggregate when used alone
and to the combined virgin aggregate and recycled material when used as a
blend. When tested in accordance with AASHTO T 27, grading shall conform to
Table 703.24-1 – Embankment Material Grading Requirements.
TABLE 703.24-1 – EMBANKMENT MATERIAL GRADING REQUIREMENTS
Sieve Size
Percent Passing by Weight
6 Inch
100
3 Inch
75 – 100
No. 4
20 – 75
No. 200
0 - 15
END OF SECTION 703
379
SECTION 717 - CULLET AND CULLET-MADE MATERIALS
717.01 Cullet and Cullet-Aggregate Mixtures as Construction Materials.
Construction-grade cullet (recycled crushed glass) shall have a uniform grading
from fine to coarse, with 100 percent of material passing the 3/8–inch sieve and
not more than 5 percent by weight passing the No. 200 sieve. Cullet shall be
blended with natural virgin aggregates in accordance with Subsections 717.02 Cullet Materials for Roadway, 717.03 - Cullet Materials for Utility Structures, or
717.04 - Cullet Materials for Drainage Systems.
Cullet content is defined as the percentage of cullet, by dry weight of the
total composite aggregate weight, of construction–grade cullet used in roadway,
utility, and drainage applications, with or without addition of natural virgin
aggregates. Finished product shall meet the specified grading requirements
shall be met.
Cullet shall be processed so as to limit the quantity of shard-like particles
in the portion retained on the No. 4 sieve to less than one percent by mass as
measured by ASTM D4791.
Debris is defined as deleterious material that includes container tops,
plastics, papers, labels, food residue, foil, wood and other non-ceramic
constituents of cullet. Debris shall be limited to maximum levels as specified in
tables 717.02-1 – Cullet in Roadway Applications, 717.03-1 – Cullet in Utility
Applications, and 717.04-1 – Cullet in Drainage Applications. In addition, the
mass of paper shall not exceed 0.05 percent of the mass of the glass cullet.
Hazardous material will not be allowed in cullet.
The percent debris shall be determined on a mass basis as follows. A
representative sample of glass cullet is placed in an oven heated to 110C (5C)
and dried to constant mass and then visually segregated into: (1) glass cullet, (2)
paper, and (3) debris as defined above other than paper. The percentage of each
component shall be determined by dividing the mass of the component by the
mass of cullet and rounded to the nearest 0.01 percent.
The cullet shall be tested as follows:
(1) Collect a minimum of one six representative sample per X cubic yards
of cullet and measure the percent debris and the percent paper, where
X = 1500 cubic yards of the final cullet-blended product times the
percent cullet in the blend.
Submit the results for all six
determinations.
(2) Request the Engineer to visually inspect the cullet stockpile. Based on
visual inspection, the results of the gradation analyses (see below) the
percent debris and the percent paper, the Engineer will determine the
380
suitability of the cullet. The Engineer has the right to conduct
independent testing to verify the submitted test results.
The final cullet-blended product shall be tested as follows: Conduct and
submit a minimum of one six gradation analysis per 1500 cubic yards of the final
cullet blended productcullet material.
The Contractor shall submit a blended aggregate design prior to use or
prior to changing either the source or amount of cullet originally approved. For
aggregate blends, the Contractor shall submit the means and method on how
uniform mixing of the recycled and virgin aggregates is ensured. Blending at the
job site shall not be permissible.
Under no circumstances shall cullet be used adjacent to or placed in
contact with any recycled concrete aggregate (RCA).
Compaction requirements shall be met for each application.
717.02
Cullet Materials for Roadways.
Cullet and cullet-aggregate
mixtures for base course (untreated or hot mix glassphalt base course mix),
subbase, and embankments shall conform to Table 717.02-1 – Cullet in
Roadway Applications. When used as a base course, it should also conform to
AASHTO Standard Specification M318-02: Glass Cullet Use for Soil-Aggregate
Base Course, except that the percent of glass cullet in the blend with unrecycled
aggregate shall be limited to 10% instead of the 20% as stated in AASHTO
M318-02.
TABLE 717.02-1 - CULLET IN ROADWAY APPLICATIONS
Roadway
Maximum Cullet Content
Maximum Debris Level
Applications
(Percent By Weight of
(Percent By Weight of
mixture)
Cullet)
Base Course
10
0.20
Subbase
10 to 25
0.20
Embankments
10 to 25
0.300.20
All crushing of the cullet necessary to meet the gradation and debris
material requirements shall be performed prior to blending.
717.03
Cullet Material for Utility Structures. Cullet for trench bedding
and backfill in cut areas more than 5 feet below road surface and in unpaved cut
areas not subject to surcharge shall conform to Table 717.03-1 – Cullet for Use
as Non-Critical Trench Backfill. Trench bedding and backfill in the following
areas shall conform to embankment requirements in Table 717.02-1 – Cullet in
Roadway Applications: cut areas 5 feet or less below road surface; cut areas
subject to surcharge; and embankment areas for full depth.
381
TABLE 717.03-1 - CULLET FOR USE AS NON-CRITICAL TRENCH BACKFILL
Utility Trench Bedding
Maximum Cullet
Maximum Debris Level
And Backfill
Content
(Percent By Weight of Cullet)
Applications
(Percent By Weight)
Drainage Pipes
100
0.20
Sewer Pipes
100
0.300.20
Electrical Conduits
100
0.300.20
Fiber Optic Lines
100
0.300.20
All crushing of the cullet necessary to meet the gradation and debris
material requirements shall be performed prior to placement.
717.04 Cullet Materials for Drainage Systems. Except in surcharged cut
areas and in embankment areas, cullet for drainage fill applications, including
drains behind retaining walls, foundation drains, drainage blankets, and French
drains shall conform to Table 717.04-1 – Cullet in Drainage Applications. In
surcharged cut areas and in embankment areas, cullet for drainage fill
applications described in this subsection shall conform to subbase requirements
in Table 717.02-1 – Cullet in Roadway Applications.
TABLE 717.04-1 - CULLET IN DRAINAGE APPLICATIONS
Maximum Cullet
Maximum Debris Level
Drainage Fill
Content
(Percent By Weight of
Applications
(Percent By Weight)
Cullet)
Retaining Walls
100
0.20
Foundation Drainage
100
0.20
Drainage Blankets
100
0.20
French Drains
100
0.20
END OF SECTION 717
382
SECTION 719 – RECYCLED CONCRETE AGGREGATE (RCA) AND RCAMADE MATERIALS
719.01 RCA and RCA-Aggregate Mixtures as Construction Materials.
RCA shall consist of material derived from the crushing of Portland cement
concrete having a grading from fine to coarse, and with 100 percent of material
passing the 1.5–inch sieve. RCA shall be blended with virgin aggregate in
accordance with Subsections 719.02 - RCA for Roadway, or 719.03 - RCA for
Utility Structures.
RCA content is defined as the percentage of RCA, by dry weight of the
total composite aggregate weight, with or without addition of virgin aggregate.
Finished product shall meet the specified grading requirements.
Deleterious material in RCA includes brick, ceramics and bituminous
concrete materials. Deleterious materials shall be limited to the maximum levels
as specified in tables 719.02-1 - RCA in Roadway Applications, or 719.03-1 RCA for Use as Non-Critical Trench Backfill. In addition, the mass of ―prohibited‖
materials such as wood, metal (excluding aluminum which is not allowed at
all in RCA. The Engineer has the right to use a non-ferrous metal detector
to detect the presence of aluminum and if present, has the right to reject
that pile of RCA.), plaster and gypsum board shall not exceed 0.1 percent of the
mass of the RCA, assuming that the RCA is obtained by crushing concrete on its
own. If the RCA is obtained by crushing concrete simultaneously with other
materials (e.g., virgin rock), the mass of ―prohibited‖ materials shall not exceed
0.03 percent of the mass of the final blended product.
When reclaimed asphalt pavement (RAP) is to be blended RCA, the RAP
shall be free of any temporary striping that contains aluminum to prevent the
aluminum from corroding. Aluminum will corrode in an alkali-rich environment,
which can exist in the presence of RCA and moisture.
The percent deleterious and prohibited materials shall be determined on a
mass basis as follows. A representative sample is dried to constant mass and
then visually segregated into: (1) aggregate, (2) deleterious materials as defined
above, and (3) ―prohibited‖ material as defined above. The percentage of each
component shall be determined by dividing the mass of the component by the
mass of the RCA if the RCA is obtained by crushing concrete on its own, or by
the mass of the final RCA-blended product if concrete is crushed with other
materials (e.g., virgin rock), and rounded to the nearest 0.01 percent.
Concrete structures that were adjacent to any aluminum that corroded in
its presence, that have suffered from sulfate attack, alkali silica reaction, or any
other known distresses shall not be crushed and used as RCA.
383
RCA shall not be used where exposure to high (as determined by the
engineer) sulfate content in the soil, ground water or other external sources is
likely. RCA shall be prohibited when the ground water is determined to be highly
brackish (near the ocean) by the Engineer to minimize the possibility of sulfate
attack.
Hazardous materials including asbestos and lead-based paint shall not be
allowed in the RCA. Provide documentation regarding each off-site source of
RCA with sufficient documentation that the off-site source locations and the RCA
are not deemed as hazardous and are NOT subject to regulation under federal or
state solid and hazardous waste laws, regulations and policies including but not
limited to RCRA Subtitles C1 and D2, and:
1. Hawaii Revised Statutes (HRS) 342J and Hawaii Administrative
(HAR) Title 11, Chapters 261 through 280 for lead-based paint
regulations, and
2. Hawaii Revised Statutes (HRS) 342P and Hawaii Administrative
(HAR) Title 11, Chapters 501 through 504 for asbestos
regulations.
Rules
waste
Rules
waste
The documentation provided shall conform to generally accepted engineering
standards for site assessments and environmental evaluations conducted by a
qualified environmental scientist. Specific environmental requirements for RCA
shall include testing that shows that the following criteria are met:
1. The RCA shall be free of lead-based paint. The U.S. Department of
Housing and Urban Development defines lead-based paint as any
paint, varnish, shellac or other coating that contains lead equal to or
greater than 1.0 mg/cm2 as measured by x-ray fluorescence (XRF) or
laboratory analysis, or 0.5% by weight (5000 g/g, 5000 ppm or 5000
mg/kg) as measured by laboratory analysis in accordance with their
Guidelines for the Evaluation and Control of Lead-Based Paint
Hazards in Housing. Note that this definition for lead-based paint
applies to undemolished concrete. In this light, the following criterion
shall be met:
The testing shall be performed only on the paint, and not on the
concrete before demolition. In this case, the total concentration of lead
in the paint shall not exceed 1.0 mg/cm 2 as measured by x-ray
fluorescence (XRF), or 0.5% by weight (5000 g/g, 5000 ppm or 5000
mg/kg) as measured by laboratory analysis. The laboratory test used
to determine lead-based paint is ―total concentration of lead.‖
In addition, the RCA shall meet the definition of inert fill as defined in
Hawaii Revised Statutes (HRS), Chapter 342H, Solid Waste Pollution.
384
2. The RCA shall be free of asbestos.
The Engineer has the right to conduct independent testing to verify the submitted
test results.
The RCA and/or blend shall be wetted prior to use to prevent fugitive dust
from becoming airborne.
The Contractor shall notify the Engineer the original source of the
aggregate including the facility name and address from where the concrete was
demolished to obtain the RCA. The Contractor shall not use RCA from unknown
sources unless certified by a qualified engineer/scientist that it is free of
aluminum, lead-based paint and asbestos. Off-site sources of RCA must have
written acceptance by the Engineer prior to blending and/or placement.
The RCA shall be further tested as follows:
(1) If the RCA is obtained by crushing concrete on its own, collect a
minimum of one representative sample per X cubic yards of RCA and
measure the percent deleterious material and the percent prohibited
material, where X = 1500 cubic yards of the final RCA-blended product
times the percent RCA in the blend. If the RCA is obtained by crushing
concrete simultaneously with other materials (e.g., virgin rock), collect
a minimum of one representative sample per 1500 cubic yards of the
final RCA-blended product and measure the percent deleterious
material and the percent prohibited material. Submit the results for all
determinations.
(2) Request the Engineer to visually inspect the RCA stockpile during and
after crushing. Based on visual inspection, the results of the gradation
analyses (see below), the percent deleterious material and the percent
prohibited material, the Engineer will determine the suitability of the
RCA. The Engineer has the right to conduct independent testing to
verify the submitted test results.
(3) Conduct and submit a minimum of one gradation analysis per 1500
cubic yards of the final RCA or its blended product.
The Contractor shall submit a blended aggregate design prior to use or
prior to changing either the source or amount of RCA originally approved. For
aggregate blends, the Contractor shall submit the means and method on how
uniform mixing of the recycled and virgin aggregates is ensured. Blending at the
job site shall not be permissible.
Furnish shipping documents and a Contractor certification that the
material delivered on-site, is in fact, that which has been documented by prior
submittal.
385
Compaction requirements shall be met for each application. The
Contractor is warned that use of rubber tired rollers may be problematic should
any fugitive steel fragments be present in the RCA during compaction.
RCA and RCA-aggregate mixtures shall not be used within 10 feet of any
metal pipes or metal structures and shall not be used within 3 feet of the ground
water table nor below the ground water table.
719.02
RCA for Roadways.
RCA and RCA-aggregate mixtures for
untreated base course, subbase, and embankments shall conform to Table
719.02-1 – RCA in Roadway Applications. When used as a base course, it
should also conform to AASHTO Standard Specification for Reclaimed Concrete
Aggregate for Unbound Soil-Aggregate Base Course, AASHTO Designation: M
319-02.
Roadway
Applications
Base Course
Subbase
Embankments
TABLE 719.02-1 - RCA IN ROADWAY APPLICATIONS
RCA Content
Maximum
Maximum Deleterious
(Percent By Weight
Deleterious
Material
of mixture)
Material
(Percent By Weight
(Percent By Weight
of Mixture)
of RCA)
100
5.00
1.25
100
5.00
1.25
100
5.00
1.25
719.03
RCA for Utility Structures. RCA for trench bedding and backfill in
cut areas more than 5 feet below road surface and in unpaved areas shall
conform to Table 719.03-1 – RCA for Use as Non-Critical Trench Backfill.
Trench bedding and backfill in the following areas shall conform to the
requirements in Table 719.02-1 – RCA in Roadway Applications: cut areas 5 feet
or less below road surface; cut areas subject to surcharge; and embankment
areas for full depth.
TABLE 719.03-1 - RCA FOR USE AS NON-CRITICAL TRENCH BACKFILL
Utility Trench Bedding
RCA Content
Maximum
Maximum Deleterious
And Backfill
(Percent By
Deleterious
Material
Applications
Weight)
Material
(Percent By Weight
(Percent By
of Mixture)
Weight
of RCA)
Drainage Pipes
100
5.00
1.25
Sewer Pipes
100
5.00
1.25
Electrical Conduits
100
5.00
1.25
Fiber Optic Lines
100
5.00
1.25
386
719.04
RCA for Drainage Systems. RCA and RCA mixtures shall be
prohibited for use in drainage fill applications, including drains behind retaining
walls, foundation drains, drainage blankets, and French drains.
END OF SECTION 719
387
SECTION 720 – RECLAIMED ASPHALT PAVEMENT (RAP) AND RAP-MADE
MATERIALS
720.01 RAP and RAP-Aggregate Mixtures as Construction Materials. RAP
shall consist of milled or crushed asphalt pavement having a gradation from fine
to coarse with 100 percent of material passing the 3/4–inch sieve. When used on
its own or when mixed with virgin aggregate, the material shall conform to the
gradation requirements as specified in the respective sections in accordance with
its intended use. RAP shall be blended with virgin aggregate in accordance with
Subsections 720.02 - RAP for Roadway, or 720.03 - RAP for Utility Structures.
RAP content is defined as the percentage of RAP, by dry weight of the
total composite aggregate weight, with or without addition of virgin aggregate.
Finished product shall meet the specified grading requirements.
Deleterious material in RAP includes debris and lumps of cohesive soil in
sufficient quantity as to be detrimental to the proper bonding, finishing or strength
of the RAP mixture. Deleterious materials shall be limited to the maximum levels
as specified in Tables 720.02-1 – RAP in Roadway Applications and 720.03-1 –
RAP in Utility Applications.
The percent deleterious material shall be determined on a mass basis as
follows. A representative sample of RAP is air-dried to constant mass and then
visually segregated into: (1) RAP and (2) deleterious materials as defined above.
The percentage of each component shall be determined by dividing the mass of
the component by the mass of RAP and rounded to the nearest 0.1 percent.
When RAP is to be blended with crushed recycled concrete aggregate
(RCA), the RAP shall be free of any temporary striping that contains aluminum to
prevent the aluminum from corroding. Aluminum will corrode in an alkali-rich
environment, which can exist in the presence of RCA and moisture.
When RAP is stockpiled from a previous State of Hawaii Department of
Transportation project and the composition of the existing pavement is known,
the Engineer may approve the material on the basis of composition. When the
composition of the RAP is not known, the RAP shall be tested as follows:
(1) Collect a minimum of one representative sample per X cubic yards of
RAP and measure the percent deleterious material, where X = 1500
cubic yards of the final RAP-blended product times the percent RAP in
the blend. Submit the results for all determinations.
(2) Request the Engineer to visually inspect the RAP stockpile. Based on
visual inspection, the results of the gradation analyses (see below) and
percent deleterious material, the Engineer will determine the suitability
of the RAP. The Engineer has the right to conduct independent testing
to verify the submitted test results.
388
The final RAP-blended product shall be tested as follows: conduct and submit a
minimum of one gradation analysis per 1500 cubic yards of the final RAP
blended product. Prior to blending, the RAP shall be air-dried to surface dry
condition. Oven drying shall not be performed on RAP.
The Contractor shall submit a blended aggregate design prior to use or
prior to changing either the source or amount of RAP originally approved. For
aggregate blends, the Contractor shall submit the means and method on how
uniform mixing of the recycled and virgin aggregates is ensured. Blending at the
job site shall not be permissible.
Compaction requirements shall be met for each application.
720.02 RAP for Roadways. RAP and RAP-aggregate mixtures for untreated
base course, subbase, and embankments shall conform to Table 720.02-1 –
RAP in Roadway Applications.
TABLE 720.02-1 - RAP IN ROADWAY APPLICATIONS
Roadway
RAP Content
Maximum Deleterious Material
Applications
(Percent By Weight of
(Percent By Weight of RAP)
mixture)
Base Course
50
3.0
Subbase
50
5.0
Embankments
50
5.0
All crushing of the RAP necessary to meet the gradation and deleterious
material requirements shall be performed prior to blending.
720.03 RAP for Utility Structures. RAP for trench bedding and backfill in cut
areas more than 5 feet below road surface and in unpaved areas shall conform
to Table 720.03-1 – RAP for Use as Non-Critical Trench Backfill. Trench bedding
and backfill in the following areas shall conform to the requirements in Table
720.02-1 – RAP in Roadway Applications: cut areas 5 feet or less below road
surface; cut areas subject to surcharge; and embankment areas for full depth.
TABLE 720.03-1 - RAP FOR USE AS NON-CRITICAL TRENCH BACKFILL
Utility Trench Bedding
RAP Content
Maximum Deleterious Material
And Backfill Applications (Percent By Weight)
(Percent By Weight of RAP)
Drainage Pipes
100
5.0
Sewer Pipes
100
5.0
Electrical Conduits
100
5.0
Fiber Optic Lines
100
5.0
All crushing of the RAP necessary to meet the gradation and deleterious
material requirements shall be performed prior to placement.
389
718.04 RAP for Drainage Systems. RAP and RAP mixtures shall be
prohibited for use in drainage fill applications, including drains behind retaining
walls, foundation drains, drainage blankets, and French drains.
END OF SECTION 720
390
Adrian Archilla