Influence of Antistripping Additives on Moisture Susceptibility of Warm Mix Asphalt Mixtures Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. Feipeng Xiao, Ph.D., P.E.1; Wenbin Zhao2; Tejash Gandhi, Ph.D.3; and Serji N. Amirkhanian, Ph.D., M.ASCE4 Abstract: Rising energy prices, global warming, and more stringent environmental regulations have resulted in an interest in warm mix asphalt 共WMA兲 technologies as a means to decrease the energy consumption and emissions associated with conventional hot mix asphalt production. However, the utilization of the hydrated lime and liquid antistripping agents 共ASA兲 in WMA mixture makes these issues more complicated. The objective of this study was to investigate and evaluate the moisture susceptibility of the mixtures containing ASA and WMA additives. The experimental design for this study included the utilizations of one binder source 共PG 64-22兲, three ASA additives and control, two WMA additives and virgin, and three aggregate sources. A total of 36 types of mixtures and 216 specimens were fabricated and tested in this study. The performed properties include indirect tensile strength 共ITS兲, tensile strength ratio 共TSR兲, flow, and toughness. The results indicated that the hydrate lime exhibits the best moisture resistance for WMA mixtures, the liquid ASA additives can increase the ITS values of the mixtures but the liquid ASA generally exhibits a weak moisture resistance compared to the hydrate lime regardless of WMA and aggregate types in this study. In addition, the wet ITS values of mixtures containing WMA additives were lower than that of the mixtures without WMA additives. DOI: 10.1061/共ASCE兲MT.1943-5533.0000111 CE Database subject headings: Viscosity; Asphalts; Stripping concrete admixtures; Tensile strength; Toughness; Moisture. Author keywords: Viscosity; Warm mix asphalt; Antistripping additive; Indirect tensile strength; Flow; Toughness; Boiling test. Introduction The phenomenon of breaking of the bond between the aggregate and the binder is known as stripping. A typical situation is the gradual loss of strength over the years, which causes many surface manifestations like rutting, corrugations, shoving, raveling, cracking, etc. 共Xiao et al. 2007, 2009; Kringos et al. 2008; Caro et al. 2008兲. To prevent moisture susceptibility, proper mix design is essential. Of the many ways to prevent stripping in a pavement, the use of antistripping agents 共ASAs兲 is the most common 共Kim and Amirkhanian 1991; Lu and Harvey 2006; Sebaaly et al. 2007兲. One of the most commonly used ASAs in the United States is hydrated lime. Others include liquid ASAs such as amines, diamines, liquid polymers, and solids like portland cement, fly ash, flue dust, etc. Pavement contractors usually prefer liquid ASAs as they are relatively easy to use 共Lu and Harvey 2006兲. However, ASAs from an approved list of sources should 1 Research Assistant Professor, Dept. of Civil Engineering, Clemson Univ., Clemson, SC 29634-0911 共corresponding author兲. E-mail: feipenx@clemson.edu 2 Graduate Research Assistant, Dept. of Civil Engineering, Clemson Univ., Clemson, SC. 3 Graduate Research Assistant, Dept. of Civil Engineering, Clemson Univ., Clemson, SC. 4 Consultant, formerly Professor, Dept. of Civil Engineering, Clemson Univ., Clemson, SC 29634-0911. Note. This manuscript was submitted on October 21, 2009; approved on April 12, 2010; published online on April 15, 2010. Discussion period open until March 1, 2011; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, Vol. 22, No. 10, October 1, 2010. ©ASCE, ISSN 08991561/2010/10-1047–1055/$25.00. not be blindly added as some ASAs are aggregate and asphalt specific, and therefore, may not be effective to be used in all mixes; they could even be detrimental at times. Thus, a proper study of each mix should be done by systematically testing the mix for moisture susceptibility using tests like indirect tensile strength 共ITS兲 in the laboratory. Recently, “warm mix asphalt” 共WMA兲 is widely being used in the hot mix asphalt 共HMA兲 industry as a means of reducing energy requirements and lowering emissions. WMA can significantly reduce the mixing and compacting temperatures of asphalt mixtures, by either lowering the viscosity of asphalt binders, or causing foaming in the binders. Reduced mixing and paving temperatures decreases the energy required to produce HMA, reduces emissions and odors from plants, and makes for better working conditions at both the plant and the paving site 共Kristjansdottir et al. 2007; Prowell et al. 2007兲. Moisture damage is usually not limited to one mechanism rather than the result of a combination of many processes. From a chemical standpoint, the literature is clear that though neither asphalt nor aggregate has a net charge, components of both have nonuniform charge distributions, and both behave as if they have charges that attract the opposite charge of the other materials 共Abo-Qudais and Mulqi 2005兲. The foaming process caused by WMA additive makes the charge redistribution more complex and thus may affect the moisture susceptibility of the mixture. Especially, at the mixture temperature of 100 to 140° C 共212 to 280° F兲, the aggregate may not be completely dried during mixing process though some states in United States and other countries have specifications that require a completely dry aggregate in WMA mixtures 共Prowell 2007; Xiao et al. 2009, 2010兲. In addition, water bearing additives are sodium-aluminumsilicate crystals, which are hydrothermally crystallized into a fine JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 / 1047 J. Mater. Civ. Eng. 2010.22:1047-1055. Table 1. Physical Properties of Aggregates Coarse aggregate A B C Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. Fine aggregate A B C LA abrasion loss 共%兲 46 32 30 Specific gravity Soundness percent loss at 5 cycles Absorption 共%兲 Dry 共BLK兲 SSD 共BLK兲 Apparent 11/2 to 3/4 3/4 to 3/8 3/8 to #4 Sand equivalent Hardness 1.10 0.70 0.50 2.690 2.770 2.630 2.720 2.780 2.640 2.770 2.820 2.660 0.2 0.4 1.1 0.1 0.6 1.7 0.1 0.9 4.1 — 38 53 5 5 6 Fineness modulus Absorption 共%兲 SSD 共BLK兲 Soundness percent loss 2.82 2.81 3.20 0.40 0.20 0.60 2.590 2.650 2.640 4.5 2.8 0.1 powder. These crystals contain large vacant spaces that can absorb or release water molecules without any damage to the crystal structure. An example of one such product is Asphamin. By adding it to the mixture at the same time as the binder, a very fine water spray is created as all the crystalline water is released, which causes a volume expansion in the binder, thereby increasing the workability and compatibility of the mixture at lower temperatures. The water absorption and release process caused by Asphamin makes the charge redistribution more complex and thus may affect the moisture susceptibility of the mixture. Although wax does not release any water molecules during blending with the binder and does not affect the moisture susceptibility of mixture in general, from chemical standpoint, the reactions among aggregate, binder, and wax are not clear. Especially, as the liquid ASAs are blended with the binder and/or wax and then mixed with aggregate and/or water bearing additive, some chemical reactions between liquid ASAs and WMA additives may occur at a high mixing temperature 共around 110° C兲 and thus may result in the loss of bond in the mixtures. There are not many research projects conducted in the area of determining the effects of the liquid ASAs with WMA additives which may result in moisture damage and further result in the failure of pavements. The goal of this study was to investigate the moisture susceptibility characteristics of the asphalt mixtures containing antistripping additives and WMA additives. Experiments were carried out to evaluate the moisture susceptibility of the mixtures using the following testing procedures such as ITS, tensile strength ratio 共TSR兲, visual boiling test, and flow and toughness. The physical and chemical properties of WMA and ASA additives are presented in Table 2. Asphamin and Sasobit were used in this study as the two WMA additives. Asphamin is a sodiumaluminum-silicate, hydrothermally crystallized as a very fine powder 共Table 2兲. It is added to the mixture at a ratio of 0.3% by weight of the mixture. Sasobit is a long chain of aliphatic hydrocarbons obtained from coal gasification using the Fischer-Tropsch process 共Table 2兲. Sasobit forms a homogeneous solution with the base binder on stirring 共1.5% by weight of the binder兲, and produces a marked reduction in the binder’s viscosity. The mixtures without any WMA additive were referred to virgin mixture. The liquid ASAs are normally added in doses between 0.25 and 0.75% by weight of the binder 共as recommended by the manufacturer兲. In this study, 0.5% dosage was used for moisture resistance evaluation. The liquid ASA may be added either to the aggregate directly, or to the heated binder 共Table 2兲. Previous research indicated that the liquid ASAs do not disintegrate at the mixing temperatures and thus are recommended to blend with the binder before mixing 共Gandhi et al. 2009兲. Hydrated lime is commonly used for antistripping of the mixture by being added to the aggregate 共1% by weight of dry aggregate兲. Mix Design, Sample Fabrication, and Testing The mix design included the aggregates used for a 12.5-mm mixture that satisfied the specifications set forth by the South Carolina Department of Transportation 共SCDOT兲. The design aggregate gradations for each aggregate source were the same when using different WMA additives 共Virgin, Asphamin, and Sa- Experimental Materials and Test Procedure Materials The experimental design detailed in this study included the use of virgin and two WMA additives 共Asphamin and Sasobit兲, lime 共referred to as ASA1兲 and two liquid ASAs 共referred to as ASA2 and ASA3兲, one binder grade 共PG 64-22兲, and three aggregate sources 共designated as A, B, and C兲. The engineering properties of coarse and fine aggregate sources are shown in Table 1. Aggregate A 共schist兲 is a metamorphic rock while Aggregate Source C 共granite兲 is composed predominantly of quartz and potassium feldspar. Aggregate B has larger percentage values of Al2O3 and SiO2 than Aggregate A. Coarse Aggregate A has the highest Los Angeles 共LA兲 abrasion loss percentage and absorption while Aggregate C has the lowest. A total of 36 types of mixtures and 216 ITS specimens were prepared for this study 共Fig. 1兲. Fig. 1. Flowchart of experimental design 1048 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 J. Mater. Civ. Eng. 2010.22:1047-1055. Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. Table 2. Physical and Chemical Properties of ASA and WMA Additives Properties Asphamin Sasobit H8 ASA1 共lime兲 Ingredients Sodium aluminosilicate Na2O, Al2O3, 2SiO2 Solid saturated hydrocarbons Calcium hydroxide Ca共OH兲2 Physical state Color Odor Molecular weight Specific gravity Vapor density Bulk density Ph values Boiling point Flashpoint Solubility in water Granular powder White Odorless 365 2 共20° C兲 — 500– 600 kg/ m3 11–12 — — Insoluble Table 3. Mixing and Compaction Temperatures of Mixtures Mixing temperatures Virgin Virgin+ ASA Virgin+ Asphamin Virgin+ Asphamin+ ASA Virgin+ Sasobit Virgin+ Sasobit+ ASA ASA3 共liquid兲 Fatty amidoamine Alkoxylated aliphatic polyamines Polyalkylene glycol mixture Polyamines; Alkylamines Pastilles, flakes Powder Liquid Liquid Off-white to pale brown White Dark brown Brown Practically odorless Odorless Mild Slight Approx. 1,000 g/mol — — — 0.9 共25° C兲 2.3–2.6 0.96–0.98 共25° C兲 — — — ⬎1 1.06 — — — — Neutral — — — — 2 , 850° C 共CaO兲 ⬎260° C 380° C 285° C 共ASTM D92兲 — ⬎200° C Closed cup: 165° C Insoluble Negligible 0.185–0.070% Slight — sobit兲 and various ASA additives. The rheological properties of asphalt binders with the WMA additives were reported elsewhere 共Gandhi 2008兲. Superpave mix design defines that the laboratory mixing and compaction temperatures can be determined by using a plot of viscosity versus temperature. There are no previous specifications available regarding the mixing and compaction temperatures for WMA mixture, however, the manufacturer reports a reduction in mixing and compaction temperatures of 30 to 50° C 共50 to 90° F兲 共Hurley and Prowell 2005a兲, and some researchers have developed guidelines for mixing and compaction temperatures when using WMA 共Hurley and Prowell 2005a,b兲. The temperatures, shown in Table 3, were determined and reported in previous research projects 共Xiao et al. 2009; Gandhi 2008兲. The mixing temperatures of materials 共Table 3兲 were employed after a series of trial processes to achieve a mixing temperature of 121– 127° C. The compaction temperature of 115– 121° C was used in this study regardless of WMA, ASA, and aggregate types. Aggregate 共A, B, C兲 mix types ASA2 共liquid兲 Aggregate 共°C兲 Binder 共°C兲 Compaction temperatures 共°C兲 145–150 145–150 121–127 121–127 121–127 121–127 145–150 145–150 121–127 121–127 121–127 121–127 132–137 132–137 115–121 115–121 115–121 115–121 For this study, the optimum binder content was defined as the amount of binder required to achieve 4.0% air voids in accordance with SCDOT volumetric specifications. The detailed mix designs are shown in Table 4. It should be noted that overall mixes from one aggregate source used the same mix design regardless of the WMA and antistrip additives. After the mix designs were completed, for each aggregate/ASA/warm asphalt additive combinations, six Superpave gyratory compacted specimens 共150 mm in diameter and 95 mm in height兲 were prepared with 7 ⫾ 1% air voids, and then the samples were tested at 25° C 共77° F兲 to determine the ITS, flow, and toughness values. Three of the samples were tested in dry condition and the other three in wet condition. The wet samples were conditioned in accordance with SC-T-70, Laboratory Determination of Moisture Susceptibility. The evaluated parameters included ITS, TSR, toughness, percentage of flow, and toughness loss. In addition, after the ITS and TSR values were determined, the mixtures that failed the SC-T-70 moisture resistance test 关wet ITS value is less than 448 kPa 共65 psi兲 or TSR less than 85%兴 were tested using the boil test to identify the moisture damage in accordance with ASTM 3625. Experimental Results and Discussions To study the effects of WMA additives, ASAs and aggregates on the mixes, ANOVA was performed to test the null hypothesis that the sample means 共ITS, flow, and toughness of each treatment兲 are not significantly different from each other at a 5% level of significance. Table 4. Mix Design of Aggregates A, B, and C Mix types OBC 共%兲 MSG VMA VFA Dust/asphalt ratio From Aggregate A 5.90 2.490 17.5 77.5 0.88 From Aggregate B 4.80 2.634 15.2 77.3 1.05 From Aggregate C 5.75 2.421 16.8 76.6 0.92 Specification 4.5–6.0 — ⬎15.0 70–80 0.60–1.20 Note: Mixes from one aggregate used a same mix design regardless of WMA and antistrip additives; OBC= optimum binder content; BSG= bulk specific gravity; MSG= maximum specific gravity; VMA= voids in mineral aggregate; and VFA= void filled with asphalt. JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 / 1049 J. Mater. Civ. Eng. 2010.22:1047-1055. Dry ITS value (kPa) 1200 Agg. A Agg. B Agg. C 1000 800 600 400 200 0 V A S V A Control S V ASA1 A S V ASA2 A S ASA3 Mixture types (a) Wet ITS value (kPa) Agg. A Agg. B Agg. C 1000 800 Min. ITS 600 400 200 0 V A S V Control A S V ASA1 A S V A ASA2 S ASA3 Mixture types (b) TSR and Boiling Test Analysis 120 Min. TSR Agg. A 100 TSR (%) Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. 1200 ITS value 关less than 448 kPa 共65 psi兲兴, the minimum wet ITS value set by SCDOT specifications. However, overall mixtures containing ASA1 共hydrated lime兲 have wet ITS values greater than 448 kPa regardless of WMA and aggregate types. Additionally, Fig. 2共b兲 shows that though additional liquid ASA2 and ASA3 increase the ITS values, some of ITS values are still less than 448 kPa. Especially, the mixtures from Aggregate A, and containing WMA additives, exhibit weak moisture resistance. Generally, the wet ITS value of the mixtures without WMA additives are greater than 448 kPa as the liquid ASAs are used for antistripping purpose. In Fig. 2共b兲, the wet ITS values of mixtures containing WMA additives are lower than that of the mixture without using WMA technologies. With respect to the WMA additive effect, in most cases, there is significant difference in wet ITS values between virgin and WMA mixtures. However, no significant difference is found in the wet ITS values between any two WMA mixtures in this study. In addition, Table 5 共c兲 shows that the mixtures with ASA1 共hydrated lime兲 from Aggregates A and B exhibit a significantly different wet ITS value compared to other mixtures. Nevertheless, there are no significant differences between any two of other ASA mixtures. Agg. B Agg. C 80 60 40 20 0 V A Control S V A S ASA1 V A ASA2 S V A S ASA3 Mixture types (c) Fig. 2. ITS and TSR values of mixtures ITS Analysis The dry ITS results shown in Fig. 2共a兲 indicate that the ITS values of specimens without WMA additive are higher while the mixtures containing Asphamin and Sasobit show lower ITS values regardless of the aggregate and ASA types. In addition, the mixtures with WMA additives have ITS value of close to 600 kPa while the ITS values of the hot mixtures are approximately in the range of 800 kPa. In most cases, the dry ITS values of samples prepared with the three aggregate sources are similar. Statistical analysis shown in Table 5 共a兲 also illustrate that there is no significant difference in ITS value among any mixtures made from three aggregates. All mixtures have ITS values greater than 448 kPa 共65 psi兲 in this study, the minimum required as per the SCDOT specifications. With respect to the WMA additive effects, in Table 5 共b兲, it can be seen that the dry ITS values of mixtures containing the three types of WMA additives 共control, Asphamin, and Sasobit兲, are significantly different. Thus the addition of WMA additives does affect the dry ITS values for the mixtures tested in this study. Regarding the effects of ASA additives, Table 5 共c兲 shows that there are no significant differences in dry ITS values of the mixtures containing various ASAs. The test results shown in Fig. 2共b兲 indicate that, in most cases, the control mixtures 共without any ASA additive兲 have a low wet The TSR results are presented in Fig. 2共c兲. It can be noted that the specimens containing 1% hydrated lime 共ASA1兲 generally have TSR values higher than 85% 共the minimum value set forth by SCDOT兲 regardless of WMA and aggregate types. However, overall mixtures without ASA additive have TSR values less than 85%. In addition, Fig. 2共c兲 also illustrates that the mixture with liquid ASA 共ASA2 and ASA3兲 generally show TSR values less than 85% though the TSR values from several mixtures containing WMA additives are greater than 85%. Fig. 2共c兲 shows that the mixtures containing liquid ASAs generally exhibit weak moisture resistance compared to the mixtures containing hydrate lime, regardless of WMA and aggregate types in this study. Thus boil tests were further performed to determine the moisture susceptibility of these mixtures through visual observation. Fig. 3 illustrates significant stripping in the mixtures made from Aggregate C and containing Asphamin additive in the boil tests 关Figs. 3共c and d兲兴. However, though the mixtures from Aggregates A or B and containing liquid ASAs had TSR values less than 85%, no obvious stripping was observed in the boil test 关Figs. 3共e and f兲兴. Deformation Analysis The deformation 共flow兲 resistance of dry ITS specimens, a measure of the material’s resistance to permanent deformation in service and related to its stiffness 共Zoorob and Suparma 2000兲, was used for moisture susceptibility analysis of the mixtures 共Roberts et al. 1996; Xiao et al. 2009兲. The flow is the total deformation value from the beginning of loading until the loads begins to decrease. As shown in Fig. 4共a兲, the deformation results indicate that, in general, the mixtures from Aggregate B show lower dry flow values than mixtures from Aggregates A and C. Beside the aggregate properties, another contributing reason is the fact that mixtures made from Aggregates A and C had higher optimum asphalt binder contents. In addition, the dry flow value of the mixtures containing Sasobit were generally lower than the hot and Asphamin mixtures. This is attributed to the stiffening of the binders as a result of crystallization of the Sasobit wax. No obvious trend in dry flow values can be found as a result of the effects of ASA additives. On the other hand, the wet flow value shown in 1050 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 J. Mater. Civ. Eng. 2010.22:1047-1055. Table 5. Statistical Analysis of Mixtures: 共a兲 Aggregate Effect; 共b兲 WMA Additive Effect; and 共c兲 ASA Effect 共a兲 ITS Flow eToughness Dry/wet A⬃B B⬃C C⬃A A⬃B B⬃C C⬃A A⬃B B⬃C C⬃A Control ASA1 ASA2 ASA3 N/N N/N N/N N/N N/N N/Y N/N N/N N/N N/Y N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N N/N 共b兲 Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. ITS Flow Toughness Dry/wet 0⬃1 0⬃2 1⬃2 0⬃1 0⬃2 1⬃2 0⬃1 0⬃2 1⬃2 Control ASA1 ASA2 ASA3 Y/Y Y/N Y/Y Y/Y Y/Y Y/N Y/Y Y/Y Y/N Y/N Y/N N/N N/N N/N N/N N/N Y/Y N/N Y/Y Y/Y Y/N N/N Y/N Y/N Y/Y Y/Y Y/Y Y/Y Y/Y Y/Y Y/Y Y/Y N/Y N/N Y/N N/N 共c兲 ITS Dry/wet C ⬃ A1 C ⬃ A2 C ⬃ A3 A1 ⬃ A2 A1 ⬃ A3 A2 ⬃ A3 Agg. A Agg. B Agg. C N/Y N/Y N/N N/N N/N N/N N/Y N/N N/N N/Y N/Y N/N N/Y N/Y N/N N/N N/N N/N N/N Y/N N/N Toughness N/N Y/N N/N N/N Y/N N/N Flow Agg. A Agg. B Agg. C N/N Y/N N/N N/N N/N N/N N/N Y/N N/N Agg. A N/Y N/N N/N N/N N/N N/N Agg. B N/N N/N N/N N/N N/N N/N Agg. C N/N N/N N/N N/N N/N N/N Note: A, B, C = Aggregates A, B, and C; 0 = Virgin; 1 = Asphamin; 2 = Sasobit; A1 = ASA1; A2 = ASA2; A3 = ASA3; Y = P-value ⬍␣ = 0.05 共significant difference兲; N = P-value ⬎␣ = 0.05 共no significant difference兲. Fig. 4共b兲 indicates that, in most cases, the mixtures with WMA additives have lower flow values than the hot mixtures except when the mixtures have hydrated lime as the ASA. Similar to the dry flow, the wet flow value of the mixtures from Aggregate A is less than that of other mixtures. Statistical analysis shown in Table 5 illustrates that the flow values of mixtures containing different aggregate sources are not significantly different regardless of WMA, ASA, and condition types. However, the Sasobit influence on the dry flow values is significant. With respect to the effect of ASA additives, there are no significant differences in the flow values 共dry and wet兲 except for the mixtures made from Aggregate B in the dry condition. Toughness Analysis Toughness is defined as the area under the tensile stressdeformation curve up to a deformation of twice that incurred at maximum tensile stress 共Freeman et al. 1989; Huang et al. 2005; Xiao et al. 2009; Xiao and Amirkhanian 2009兲. The toughness results of wet ITS specimens are shown in Fig. 5 and the statistical analysis is presented in Table 5. It can be noted that, in most cases, the toughness values of the specimens containing WMA additives are less than those values of hot mixtures, regardless of the aggregate, ASA, and condition types 共dry and wet兲. This could be as a result of the lower oxidation of the binders due to the lower mixing and compaction temperatures of warm mixes. In addition, the WMA mixtures mixed with hydrated lime generally exhibited the highest toughness values. Statistical analysis shown in Table 5 共a兲 indicates that the aggregate effect on the toughness is not significant. The effect of WMA is shown in Table 5 共b兲; it can be noted that the hot mixtures have a significantly different toughness value compared to the mixtures containing WMA additives. But, there is no significant difference, in general, between the two WMA mixtures in terms of the toughness values. With respect to the ASA effect, Table 5 共c兲 illustrates that there are no significant differences in the toughness values among the mixtures containing different ASA additives. Percentage of Flow and Toughness Loss Analysis If the percentage of flow loss 共PFL兲 and the percentage of toughness loss 共PTL兲 values are positive due to the fact that the dry toughness values are greater than wet, this also means that, under the moisture treatment, the mixtures do not undergo higher defor- JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 / 1051 J. Mater. Civ. Eng. 2010.22:1047-1055. Dry toughness value (1/N) (a) (b) 8.0 Agg. A Agg. B Agg. C 6.0 4.0 2.0 0.0 V A S V Control A S V ASA1 A S V ASA2 A S ASA3 Mixture types (d) (e) 8.0 Agg. A Agg. B Agg. C 6.0 4.0 2.0 0.0 (f) V A Control Fig. 3. Boiling testing: 关共a兲 and 共b兲兴 boiling process; 关共c兲 and 共d兲兴 stripped sample; and 关共e兲 and 共f兲兴 no stripped sample S V A S ASA1 V A S V ASA2 A S ASA3 Mixture types (b) mation. The PFL results shown in Table 6 indicate that the mixtures from Aggregate A and containing WMA additives generally have positive PFL values 共i.e., dry ITS specimens exhibit greater flow values than wet ones兲 while most of the mixtures from Aggregates B and C and without WMA additive were affected by moisture since the wet specimens show greater flow values. In addition, the PTL values indicate the toughness values of overall mixtures are generally greater than 0. The dry specimens have greater toughness values than the wet ones except for several mixtures with the hydrated lime. Table 6 shows that the wet speci- Dry flow value (mm) 6.0 Agg. A Agg. B Agg. C 5.0 4.0 3.0 2.0 1.0 0.0 V A S V Control A S V ASA1 A S V ASA2 A S ASA3 Mixture types (a) Fig. 5. Toughness values of mixtures mens with hydrated lime might have positive PFL and PTL values, and thus hydrated lime is effective in improving the moisture resistance of the mixtures. Correlation Analysis of Toughness with ITS Values Generally, greater toughness value means greater ITS and/or deformation values and results in better moisture resistance. Correlation of the two variables was developed using a simple linear analysis. In an attempt to perform the correlation analysis for the mixtures 共dry and wet兲 in terms of the aggregate type, the equations presented in Fig. 6 were used. Each of the linear equations had a high coefficient of determination 共R2兲 value. For example, the R2 values from the equations developed for the dry and wet specimens are greater than 0.72 and 0.57, respectively. This means that there is a good correction between the toughness and ITS values regardless of the dry and wet conditions. In addition, the slopes of overall equations are greater than 0, which indicates that the increase of ITS value generally results in an increase of the toughness value regardless of aggregate, ASA, and WMA types in this study. 6.0 Wet flow value (mm) Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. (c) Wet toughness value (1/N) (a) Agg. A Agg. B Agg. C 5.0 Distribution Analysis of ITS Value 4.0 3.0 2.0 1.0 0.0 V A Control S V A S ASA1 V A S ASA2 Mixture types (b) Fig. 4. Flow values of mixtures V A ASA3 S In order to further study the effects of aggregate source, WMA additive, and ASA additive on the ITS values, the ITS range distribution was studied for the different mixtures. This distribution analysis was categorized in to dry and wet groups. Figs. 7共a and b兲 show the influences of aggregate sources. In Fig. 7共a兲, the dry ITS peak values of the mixtures containing three aggregates are close to 600–700 kPa and none of the ITS values are less than 500 kPa. However, Fig. 7共b兲 illustrates that the ITS values of the mixtures containing Aggregates A and C are in the range of 500– 600 kPa 共the highest distribution for the wet specimens兲. In addition, a greater total percentage wet ITS of the mixtures from 1052 / JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 J. Mater. Civ. Eng. 2010.22:1047-1055. Table 6. Percentage of Flow and Toughness Loss Values PFL WMA type Agg. A V A S ASA1 V A S ASA2 V A S ASA3 V A S Note: V = Virgin; A = Asphamin; Sa= Sasobi; 8.05 ⫺7.11 ⫺8.16 43.16 16.22 24.69 6.38 ⫺1.12 4.85 ⫺11.27 5.58 ⫺38.01 ⫺7.01 ⫺3.87 12.90 27.83 9.21 29.00 2.48 ⫺12.85 12.87 22.16 3.66 2.78 PFL and PTL= 共dry− wet兲 ⫻ 100/ dry. Aggregate B is located in the range of 100–400 kPa, below the passing ITS value of 448 kPa. It is considered that the effects of moisture on wet ITS values may be significant as the optimum asphalt binder content of mixtures from Aggregate B is relatively lower than other mixtures regarding additional antistrip and WMA additives 共Table 4兲. With respect to the effect of ASA additives, in Figs. 7共c and d兲, it can be noted that the peak ITS distribution of control mixtures are generally in the range of 600–700 kPa and 300–400 kPa for the dry and wet specimens, respectively. However, the mixtures with ASA1 additive have the dry and wet ITS values in the range of 700–800 and 800–900 kPa 共ITS peak distribution兲, respectively. Generally, the addition of ASA1 additive 共hydrated lime兲 is able to make the ITS peak distribution move forward right of x-axle, resulting in an increase of ITS values 共dry and wet兲. With respect to the influence of WMA additives, Figs. 7共e and f兲 indicate that the mixtures containing WMA additives generally exhibit a dry ITS peak distribution in the range of 500–700 kPa while hot mixtures in the range of 800–900 kPa. Similarly, the wet ITS value of hot mixtures is higher compared to warm mixes. It seems that the mixtures with WMA additives exhibits a weaker moisture resistance compared to the hot mixtures in accordance with its ITS distribution range in this study. Dry Toughness Value (1/N) Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. Control Agg. B 10.0 8.0 6.0 A B B: y = 0.0134x - 5.2163 R² = 0.9021 C C: y = 0.0125x - 4.3487 R² = 0.7291 4.0 A: y = 0.0097x - 3.3801 R² = 0.8258 2.0 0.0 400 600 800 1000 1200 Agg. C Agg. A Agg. B Agg. C ⫺6.90 25.00 18.52 ⫺2.32 ⫺1.12 6.01 ⫺14.68 2.13 10.81 ⫺17.69 ⫺30.34 4.55 49.76 62.29 45.64 ⫺11.40 ⫺10.34 0.33 21.33 54.73 23.57 16.13 34.31 22.27 18.87 61.87 40.25 1.99 ⫺3.79 ⫺15.04 16.85 37.79 3.96 13.04 23.80 3.77 23.30 74.01 40.48 2.52 14.79 20.80 4.85 36.49 24.66 19.89 6.27 8.81 Findings and Conclusions The following conclusions were drawn based upon the experimental results obtained from the WMA mixtures containing various ASA additives: • In general, the dry ITS values of the mixtures without WMA additives are higher while the mixtures containing Asphamin and Sasobit show lower ITS values regardless of the aggregate and ASA types. There are significantly different dry ITS values among the mixtures containing three types of WMA additives 共control, Asphamin, and Sasobit兲, thus the addition of WMA additives does affect the dry ITS values for the mixtures tested in this study. In addition, there is no significant difference in ITS values among any mixtures made from the three aggregates and ASA additives. • The mixtures containing ASA1 共hydrated lime兲 had wet ITS values greater than 448 kPa regardless of WMA and aggregate types while adding liquid ASA2 and ASA3 only slightly increased the wet ITS values. In addition, the wet ITS values of mixtures containing WMA additives are lower than that of the mixtures without the WMA additives. Moreover, statistical analysis shows that no significant difference is found between any two WMA mixtures and any two mixtures containing liquid ASA additives in this study. Wet Toughness Value (1/N) ASA type PTL 10.0 A B C B: y = 0.009x - 1.6626 R² = 0.5747 8.0 6.0 C: y = 0.0086x - 1.1393 R² = 0.8809 4.0 2.0 A: y = 0.0111x - 3.4701 R² = 0.7805 0.0 0 200 Dry ITS value (kPa) (a) 400 600 800 1000 Wet ITS value (kPa) (b) Fig. 6. Correlation analysis of ITS with toughness values JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / OCTOBER 2010 / 1053 J. Mater. Civ. Eng. 2010.22:1047-1055. 40 30 50 A B C Distribution (%) Distribution (%) 50 20 10 A B C 40 30 20 10 0 0 0- 100- 200- 300- 400- 500- 600- 700- 800- 900100 200 300 400 500 600 700 800 900 1000 400- 500- 600- 700- 800- 900- 1000-1100500 600 700 800 900 1000 1100 1200 Dry ITS value (kPa) Wet ITS value (kPa) Control ASA1 ASA2 ASA3 +ASA 60 40 20 Distribution (%) Distribution (%) (b) 0 400-500 500-600 600-700 700-800 800-900 9001000 80 40 20 0 100- 200- 300- 400- 500- 600- 700- 800- 900- 1000200 300 400 500 600 700 800 900 1000 1100 10001100 Wet ITS value (kPa) 60 Virgin (d) Asphamin Sasobit +WMA 40 20 0 400-500 500-600 600-700 700-800 800-900 9001000 10001100 Distribution (%) (c) 80 Control ASA1 ASA2 ASA3 +ASA 60 Dry ITS value (kPa) Distribution (%) Downloaded from ascelibrary.org by Tongji University on 12/20/14. Copyright ASCE. For personal use only; all rights reserved. (a) 80 80 Virgin Asphamin 60 Sasobit +WMA 40 20 0 100- 200- 300- 400- 500- 600- 700- 800- 900- 1000200 300 400 500 600 700 800 900 1000 1100 Dry ITS value (kPa) Wet ITS value (kPa) (e) (f) Fig. 7. Distribution analysis of ITS values: 关共a兲 and 共b兲兴 aggregate effect; 关共c兲 and 共d兲兴 ASA effect; and 关共e兲 and 共f兲兴 WMA additive effect • The specimens containing 1% hydrated lime generally have TSR values higher than 85% regardless of WMA and aggregate type. The TSR results indicate that the liquid ASA generally exhibit a weaker moisture resistance compared to the hydrate lime, regardless of WMA and aggregate types in this study. Boiling test indicated that the mixture made with Aggregate C exhibits significant stripping damage while other mixtures do not show any noticeably visual stripping problem. • There are no significant differences in flow values between any two mixtures from various aggregates regardless of WMA, ASA, and condition types. With respect to the effect of ASA additive, there are no significant differences in the flow values 共dry and wet兲 except for the mixtures made from Aggregate B in the dry condition. In addition, in most cases, the mixtures with WMA additives had lower flow value than the virgin mixtures. • Statistical analysis illustrate that, in most cases, the toughness values of the specimens containing WMA additives are less than those values of virgin mixtures regardless of the aggregate, ASA, and condition types 共dry and wet兲. In addition, the WMA mixtures mixed with hydrated lime generally had the highest toughness values. On the other hand, there are no significant differences in the toughness values among the mixtures with all the ASA additives. • The distribution analysis indicates that additional ASA additive is able to make the ITS peak distribution move forward right of x-axle, indicating an increase of ITS values 共dry and wet兲 while the mixtures with WMA additives exhibit a weak moisture resistance in accordance with its ITS distribution range in this study. Acknowledgments Financial support was made possible through a grant from South Carolina’s Department of Health and Environment Control 共DHEC兲 and the Asphalt Rubber Technology Service 共ARTS兲 of Clemson University. References Abo-Qudais, S., and Mulqi, M. W. 共2005兲. “New chemical antistripping additives for bituminous mixtures.” J. ASTM Int., 2共8兲, 87–97. Caro, S., Masad, E., Bhasin, A., and Little, D. N. 共2008兲. “Moisture susceptibility of asphalt mixtures, Part 1: Mechanisms.” Int. J. Pavement Eng., 9共2兲, 81–98. Freeman, R. B., Burati, J. 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