ABSTRACT This paper presents an overview of research efforts undertaken to evaluate the sensitivi... more ABSTRACT This paper presents an overview of research efforts undertaken to evaluate the sensitivity of several mixture performance tests on identical Performance Grade (PG) binders obtained from different suppliers in the State of Arizona. The laboratory testing program included the dynamic modulus, static creep / flow time, and the repeated load / flow number tests. Asphalt mixtures were collected from four sections on a project constructed in northern Arizona. This project was unique in that all four asphalt concrete mixtures had the same aggregate structure, but used PG 76-16 binders obtained from four different suppliers. Dynamic modulus, flow time and flow number test results were evaluated for each of the four asphalt concrete mixtures. Based on the test results, the tests distinguished between field mixtures produced with asphalt binders from different suppliers. This was confirmed with MEPDG analysis that predicted higher rutting and fatigue results for mixtures with low dynamic modulus values. In addition, the binder and mixture data from the Arizona project were input into the Mechanistic-Empirical Pavement Design Guide (MEPDG) and design simulations were run to compare rutting and fatigue cracking associated with each of the four PG76-16 binders included in this study. Significant statistical differences in both distress mechanisms were also observed for the different mixes.
Load associated fatigue cracking is one of the major distress types occurring in flexible pavemen... more Load associated fatigue cracking is one of the major distress types occurring in flexible pavements. Beam fatigue testing has been used for several decades and is considered an integral part of advanced characterization procedures. However, there have been several fatigue failure analysis methods based on the failure stiffness of the mixture. These methods may not produce the same results, and vary depending on the method of detecting the failure point. In this paper, beam fatigue test results conducted at Arizona State University were used for the analysis. The mixtures included conventional, Asphalt Rubber (AR), and Fiber-Reinforced (Aramid and Polyolefin) asphalt mixtures. Deflection controlled fatigue tests were conducted according to American Association of State Highway and Transportation Officials (AASHTO T321) procedure at three temperatures. Paired-t statistical analysis approach was utilized to compare five different fatigue failure methods. These methods are commonly know...
7th RILEM International Conference on Cracking in Pavements, 2012
ABSTRACT The main purpose of this paper was to document the laboratory experimental program resul... more ABSTRACT The main purpose of this paper was to document the laboratory experimental program results conducted at Arizona State University (ASU) and Swedish National Road and Transportation Research Institute (VTI) to obtain material properties and performance characteristics for a “reference gap” , “polymer-modified gap”, and “rubber-modified gap” graded mixtures placed on the Swedish Malmo E18 Highway. The advanced material characterization tests included: bending beam for fatigue cracking evaluation and C* line integral test along with Wheel Tracking Tests (WTT) to evaluate crack propagation. The test results were used to compare the performance of the rubber-modified gap graded mixture to a polymer-modified as well as a reference gap mixture. The results showed that the expected fatigue life for the rubber-modified gap graded mixture was the highest followed by the polymer-modified and then the reference gap mixture. Furthermore, the crack propagation test results showed that the rubber-modified gap graded mixture had higher resistance to crack propagation; also, it was observed that rubber-modified mix satisfied Swedish requirements of the corresponding wear layer coatings. To make an overall assessment and verify the laboratory results, it was recommended that a multi-year continuous field monitoring and laboratory evaluation of the test sections is essential.
ABSTRACT A long lasting flexible pavement has been the goal of the pavement community for many ye... more ABSTRACT A long lasting flexible pavement has been the goal of the pavement community for many years. Designing perpetual pavements requires the knowledge of the stresses or strains, below which damage does not occur or can be healed during unloading. The endurance limit, as applied to hot mix asphalt (HMA) and flexible pavement design, is the strain or stress level below which the HMA would endure indefinite fatigue load repetitions and the pavement would not experience bottom-up fatigue cracking. The purpose of this study is to determine the endurance limit for HMA under different conditions using laboratory beam fatigue tests. The method used in this study assumes that if stresses or strains are kept below certain level, fatigue damage may not occur or can be healed during unloading. Relating healing to endurance limit makes this procedure unique compared to previous studies that investigated these concepts separately. An extensive laboratory beam fatigue testing program covering a wide range of asphalt mixtures was conducted according to AASHTO T321-03 test procedure as a part of the NCHRP 9-44A project. The endurance limit was determined when no accumulated damage occurred indicating complete healing during the rest period after each load application. The endurance limit varied between 22 and 264 micro-strains (µs) depending on the applied strain, binder grade, binder content, air void, temperature and the rest period between load applications when a 0.1 loading cycles are used. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled.
ABSTRACT In this study, a laboratory experimental program was conducted to obtain material proper... more ABSTRACT In this study, a laboratory experimental program was conducted to obtain material properties and performance characteristics for a “Reference Gap” and “Asphalt Rubber (AR) Gap” graded mixtures that were used on the Swedish Malmo E-06 Highway. The advanced material characterization tests included: Dynamic (Complex) Modulus for stiffness evaluation, repeated load for permanent deformation characterization, beam fatigue for crack evaluation, and C* Integral test to evaluate crack propagation. The data was used to compare the performance of the AR Gap Graded mixture to the Reference Gap. The results showed that the AR gap graded mix would provide better resistance to low temperature cracking and permanent deformation. The expected fatigue life for the AR gap graded mixture was higher than the reference mix for the existing highway conditions. Furthermore, the crack propagation tests showed that the AR gap graded mixture has higher resistance to crack propagation.
Bottom-up fatigue cracking is one of the main distress types in flexible pavement. Current design... more Bottom-up fatigue cracking is one of the main distress types in flexible pavement. Current design methods of flexible pavement assume that cumulative damage occurs where each load cycle uses up a portion of the finite fatigue life of the asphalt layer regardless of load magnitude or traffic volume. The concept of endurance limit (EL) assumes that there is a strain value below which fatigue damage may not occur or can be healed during unloading. The fact that traffic loads are separated by “rest periods” may allow for partial or full healing of the accumulated damage, which in turn increases the number of load repetitions before failure. Therefore, if the pavement is thick enough to keep strains below the endurance limit, the fatigue life of the pavement can be considerably extended. This concept has significant design and economic implications. In 1972, Monismith and McLean (1) first proposed an endurance limit of 70 microstrain for asphalt pavements. More recently, Nishizawa (2) an...
Transportation Research Record: Journal of the Transportation Research Board, 2014
ABSTRACT The concept of Endurance Limit (EL) assumes that there is a strain value below which the... more ABSTRACT The concept of Endurance Limit (EL) assumes that there is a strain value below which the net fatigue damage occurring during a load cycle is zero. The fact that real traffic loads are separated by rest periods may allow for partial or full healing of the micro-cracks, which can affect this EL. If the asphalt layer thickness is controlled to keep strains below the EL, the fatigue life of the pavement can be considerably extended. In this paper it is hypothesized that the EL in asphalt concrete develops from the interaction and balance of damage and healing during a load cycle. This hypothesis forms the basis of the testing and analysis program, which evaluates the effects of air voids, asphalt content, rest period, and temperature on the EL limit. Two types of fatigue tests are conducted; beam (flexural) and uniaxial. A regression model is also developed based on the results of each test and used to obtain the EL values. This paper compares fatigue damage, healing and EL results from the two tests under similar conditions. The comparison shows that the beam fatigue test yields less overall fatigue damage and less healing as compared to the uniaxial fatigue test. Beam fatigue yields 8 to 14 times longer fatigue lives, while uniaxial fatigue yields higher healing (10.4 times for the only available case). Since damage and healing combine to govern the EL, the two tests produced close EL values where the overall uniaxial EL values were 12% less compared to the beam fatigue EL values.
Fatigue endurance limit (FEL) is a key parameter for designing perpetual pavements to mitigate bo... more Fatigue endurance limit (FEL) is a key parameter for designing perpetual pavements to mitigate bottom-up fatigue cracking. This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 9-44A to develop a framework and mathematical methodology to determine the FEL using the uniaxial fatigue test. In this unique procedure, the FEL is defined as the allowable tensile strains at which a balance takes place between the fatigue damage during loading, and the healing during the rest periods between loading pulses. The viscoelastic continuum damage model was used to isolate time dependent damage and healing in hot mix asphalt from that due to fatigue. The laboratory testing program consisted of dynamic modulus testing to estimate the viscoelastic properties of the asphalt mixtures, and uniaxial fatigue test experiment conducted with and without rest periods. Five factors that affect the fatigue and healing behavior of asphalt mixtures were evaluated: ...
Transportation Research Record: Journal of the Transportation Research Board, 2013
ABSTRACT One of the main requirements of designing perpetual pavements is to determine the endura... more ABSTRACT One of the main requirements of designing perpetual pavements is to determine the endurance limit of hot-mix asphalt (HMA). The endurance limit, as applied to HMA and flexible pavement design, is the strain or stress level below which the HMA would endure indefinite fatigue load repetitions and the pavement would not experience bottom-up fatigue cracking. The purpose of this study is to validate the endurance limit for HMA by using laboratory beam fatigue tests. A rational procedure was developed to determine the endurance limit of HMA attributable to healing that occurs during the rest periods between loading cycles. Relating healing to endurance limit makes this procedure unique compared with previous research projects that investigated these concepts separately. An extensive laboratory testing program was conducted according to AASHTO T 321-03 test procedure as a part of NCHRP Project 9-44A. Six factors that affected the fatigue response of HMA were evaluated: binder grade, binder content, air voids, test temperature, rest period, and applied strain. The endurance limit was determined when no accumulated damage occurred and indicated complete healing during the rest period after each load application. A threshold rest period of about 5 s for a load duration of 0.1 s—beyond which no more healing was gained—was obtained. HMA exhibits endurance limits ranging from 37 to 246 microstrains, depending on mixture properties and environmental conditions. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled.
ABSTRACT The properties of asphalt concrete are the result of many interdependent physical and ch... more ABSTRACT The properties of asphalt concrete are the result of many interdependent physical and chemical mechanisms occurring across multiple length scales. Admixtures such as hydrated lime (HL) and portland cement (PC) are known to affect the behaviors of asphalt concrete at the macroscale, but their contribution at other scales and influences on overall performance of the material are not well understood. This paper presents findings from a study to evaluate the potential for HL and PC for mitigating the effects of asphalt concrete aging with respect to modulus and fatigue resistance. The properties of interest were evaluated at multiple scales which involved binder, mastic, and mixture testing. Rheological analyses of aged and un-aged control, HL modified and PC modified mastics indicate that HL possesses greater potential to mitigate aging than PC. In mixture testing, the modulus results showed trends similar to that of mastics wherein the HL modified samples were the stiffest and also showed greater potential to mitigate aging. As expected, the relative increase in stiffness and relative potential to mitigate aging, averaged across temperatures, was found to be higher in mastics than the mixtures. The results from uniaxial fatigue test show that HL mixtures possess higher fatigue resistance when aged, thus less negative impacts from the oxidation process. Magnification of aging mitigation potential at the mastic scale and its direct correlation to fatigue behavior, explains why multiple scale evaluations can be useful in evaluating the true benefits of the admixtures.
This study was an investigation to identify whether the American Association of State Highway and... more This study was an investigation to identify whether the American Association of State Highway and Transportation Officials (AASHTO) T 283 Modified Lottman moisture susceptibility test can be successfully applied to assess moisture damage of the AR mixtures used in Arizona. A secondary objective of this study was to assess if the AASHTO TP 62-03 Dynamic Modulus E* laboratory test implemented in the pavement community is useful in assessing the susceptibility of conventional, HMA and AR mixtures. The research scope of work included conducting laboratory testing program on AR and conventional HMA mixes using AASHTO T 283 to determine the indirect tensile strength and Tensile Strength Ration (TSR). The AASHTO TP 62-03 Dynamic Modulus E* tests were then used to determine the percent retained stiffness, a term that was referred to as E* Stiffness Ratio (ESR). The TSR values were then compared to the ESR values for both conventional as well as AR mixes, and statistical analyses were conduc...
A recent Arizona State University study was conducted to evaluate two Warm Mix Asphalt (WMA) mixt... more A recent Arizona State University study was conducted to evaluate two Warm Mix Asphalt (WMA) mixturess. The evaluation included three laboratory tests on field cores as well as lab compacted specimens from an Arizona Department of Transportation (ADOT) project that involved two WMA test sections. The first section used a foamed-based WMA admixture, while the second section used a chemical-based WMA admixture. All laboratory testing were conducted at 70 °F (21 °C) and included; the dynamic modulus (E*), indirect tensile strength (IDT) and moisture damage evaluation using AASHTO T-283 test procedure. The testing plan of the foaming-based, chemical-based, and control sections of the study included field-cored specimens as well as laboratory specimens compacted at two different temperatures 270 °F (132 °C) and 310 °F (154 °C). On the foaming section of the study, field-stacked specimens showed statistically higher dynamic modulus compared to the lab-compacted specimens, meanwhile, the l...
Many well-constructed flexible pavements with a thick Hot Mix Asphalt (HMA) structure have been i... more Many well-constructed flexible pavements with a thick Hot Mix Asphalt (HMA) structure have been in service for 40 or more years without any evidence of fatigue cracking. This field experience suggests that an endurance limit, that is, a level of strain below which an asphalt concrete pavement will not exhibit fatigue cracks, is a valid concept for HMA mixtures. Several studies have been conducted to confirm the existence of an HMA fatigue endurance limit through an extensive program of laboratory testing, which further suggested that the endurance limit is influenced by HMA mixture and binder properties. NCHRP Project 9-44A was designed to extend the results and findings of previous studies with particular attention to the influence of asphalt binder and mixture properties on the endurance limit and to the relationship of the endurance limit to the phenomenon of healing hypothesized to occur in asphalt mixtures during the rest period between load applications in the laboratory and i...
ABSTRACT This paper presents an overview of research efforts undertaken to evaluate the sensitivi... more ABSTRACT This paper presents an overview of research efforts undertaken to evaluate the sensitivity of several mixture performance tests on identical Performance Grade (PG) binders obtained from different suppliers in the State of Arizona. The laboratory testing program included the dynamic modulus, static creep / flow time, and the repeated load / flow number tests. Asphalt mixtures were collected from four sections on a project constructed in northern Arizona. This project was unique in that all four asphalt concrete mixtures had the same aggregate structure, but used PG 76-16 binders obtained from four different suppliers. Dynamic modulus, flow time and flow number test results were evaluated for each of the four asphalt concrete mixtures. Based on the test results, the tests distinguished between field mixtures produced with asphalt binders from different suppliers. This was confirmed with MEPDG analysis that predicted higher rutting and fatigue results for mixtures with low dynamic modulus values. In addition, the binder and mixture data from the Arizona project were input into the Mechanistic-Empirical Pavement Design Guide (MEPDG) and design simulations were run to compare rutting and fatigue cracking associated with each of the four PG76-16 binders included in this study. Significant statistical differences in both distress mechanisms were also observed for the different mixes.
Load associated fatigue cracking is one of the major distress types occurring in flexible pavemen... more Load associated fatigue cracking is one of the major distress types occurring in flexible pavements. Beam fatigue testing has been used for several decades and is considered an integral part of advanced characterization procedures. However, there have been several fatigue failure analysis methods based on the failure stiffness of the mixture. These methods may not produce the same results, and vary depending on the method of detecting the failure point. In this paper, beam fatigue test results conducted at Arizona State University were used for the analysis. The mixtures included conventional, Asphalt Rubber (AR), and Fiber-Reinforced (Aramid and Polyolefin) asphalt mixtures. Deflection controlled fatigue tests were conducted according to American Association of State Highway and Transportation Officials (AASHTO T321) procedure at three temperatures. Paired-t statistical analysis approach was utilized to compare five different fatigue failure methods. These methods are commonly know...
7th RILEM International Conference on Cracking in Pavements, 2012
ABSTRACT The main purpose of this paper was to document the laboratory experimental program resul... more ABSTRACT The main purpose of this paper was to document the laboratory experimental program results conducted at Arizona State University (ASU) and Swedish National Road and Transportation Research Institute (VTI) to obtain material properties and performance characteristics for a “reference gap” , “polymer-modified gap”, and “rubber-modified gap” graded mixtures placed on the Swedish Malmo E18 Highway. The advanced material characterization tests included: bending beam for fatigue cracking evaluation and C* line integral test along with Wheel Tracking Tests (WTT) to evaluate crack propagation. The test results were used to compare the performance of the rubber-modified gap graded mixture to a polymer-modified as well as a reference gap mixture. The results showed that the expected fatigue life for the rubber-modified gap graded mixture was the highest followed by the polymer-modified and then the reference gap mixture. Furthermore, the crack propagation test results showed that the rubber-modified gap graded mixture had higher resistance to crack propagation; also, it was observed that rubber-modified mix satisfied Swedish requirements of the corresponding wear layer coatings. To make an overall assessment and verify the laboratory results, it was recommended that a multi-year continuous field monitoring and laboratory evaluation of the test sections is essential.
ABSTRACT A long lasting flexible pavement has been the goal of the pavement community for many ye... more ABSTRACT A long lasting flexible pavement has been the goal of the pavement community for many years. Designing perpetual pavements requires the knowledge of the stresses or strains, below which damage does not occur or can be healed during unloading. The endurance limit, as applied to hot mix asphalt (HMA) and flexible pavement design, is the strain or stress level below which the HMA would endure indefinite fatigue load repetitions and the pavement would not experience bottom-up fatigue cracking. The purpose of this study is to determine the endurance limit for HMA under different conditions using laboratory beam fatigue tests. The method used in this study assumes that if stresses or strains are kept below certain level, fatigue damage may not occur or can be healed during unloading. Relating healing to endurance limit makes this procedure unique compared to previous studies that investigated these concepts separately. An extensive laboratory beam fatigue testing program covering a wide range of asphalt mixtures was conducted according to AASHTO T321-03 test procedure as a part of the NCHRP 9-44A project. The endurance limit was determined when no accumulated damage occurred indicating complete healing during the rest period after each load application. The endurance limit varied between 22 and 264 micro-strains (µs) depending on the applied strain, binder grade, binder content, air void, temperature and the rest period between load applications when a 0.1 loading cycles are used. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled.
ABSTRACT In this study, a laboratory experimental program was conducted to obtain material proper... more ABSTRACT In this study, a laboratory experimental program was conducted to obtain material properties and performance characteristics for a “Reference Gap” and “Asphalt Rubber (AR) Gap” graded mixtures that were used on the Swedish Malmo E-06 Highway. The advanced material characterization tests included: Dynamic (Complex) Modulus for stiffness evaluation, repeated load for permanent deformation characterization, beam fatigue for crack evaluation, and C* Integral test to evaluate crack propagation. The data was used to compare the performance of the AR Gap Graded mixture to the Reference Gap. The results showed that the AR gap graded mix would provide better resistance to low temperature cracking and permanent deformation. The expected fatigue life for the AR gap graded mixture was higher than the reference mix for the existing highway conditions. Furthermore, the crack propagation tests showed that the AR gap graded mixture has higher resistance to crack propagation.
Bottom-up fatigue cracking is one of the main distress types in flexible pavement. Current design... more Bottom-up fatigue cracking is one of the main distress types in flexible pavement. Current design methods of flexible pavement assume that cumulative damage occurs where each load cycle uses up a portion of the finite fatigue life of the asphalt layer regardless of load magnitude or traffic volume. The concept of endurance limit (EL) assumes that there is a strain value below which fatigue damage may not occur or can be healed during unloading. The fact that traffic loads are separated by “rest periods” may allow for partial or full healing of the accumulated damage, which in turn increases the number of load repetitions before failure. Therefore, if the pavement is thick enough to keep strains below the endurance limit, the fatigue life of the pavement can be considerably extended. This concept has significant design and economic implications. In 1972, Monismith and McLean (1) first proposed an endurance limit of 70 microstrain for asphalt pavements. More recently, Nishizawa (2) an...
Transportation Research Record: Journal of the Transportation Research Board, 2014
ABSTRACT The concept of Endurance Limit (EL) assumes that there is a strain value below which the... more ABSTRACT The concept of Endurance Limit (EL) assumes that there is a strain value below which the net fatigue damage occurring during a load cycle is zero. The fact that real traffic loads are separated by rest periods may allow for partial or full healing of the micro-cracks, which can affect this EL. If the asphalt layer thickness is controlled to keep strains below the EL, the fatigue life of the pavement can be considerably extended. In this paper it is hypothesized that the EL in asphalt concrete develops from the interaction and balance of damage and healing during a load cycle. This hypothesis forms the basis of the testing and analysis program, which evaluates the effects of air voids, asphalt content, rest period, and temperature on the EL limit. Two types of fatigue tests are conducted; beam (flexural) and uniaxial. A regression model is also developed based on the results of each test and used to obtain the EL values. This paper compares fatigue damage, healing and EL results from the two tests under similar conditions. The comparison shows that the beam fatigue test yields less overall fatigue damage and less healing as compared to the uniaxial fatigue test. Beam fatigue yields 8 to 14 times longer fatigue lives, while uniaxial fatigue yields higher healing (10.4 times for the only available case). Since damage and healing combine to govern the EL, the two tests produced close EL values where the overall uniaxial EL values were 12% less compared to the beam fatigue EL values.
Fatigue endurance limit (FEL) is a key parameter for designing perpetual pavements to mitigate bo... more Fatigue endurance limit (FEL) is a key parameter for designing perpetual pavements to mitigate bottom-up fatigue cracking. This study was conducted as part of the National Cooperative Highway Research Program (NCHRP) Project 9-44A to develop a framework and mathematical methodology to determine the FEL using the uniaxial fatigue test. In this unique procedure, the FEL is defined as the allowable tensile strains at which a balance takes place between the fatigue damage during loading, and the healing during the rest periods between loading pulses. The viscoelastic continuum damage model was used to isolate time dependent damage and healing in hot mix asphalt from that due to fatigue. The laboratory testing program consisted of dynamic modulus testing to estimate the viscoelastic properties of the asphalt mixtures, and uniaxial fatigue test experiment conducted with and without rest periods. Five factors that affect the fatigue and healing behavior of asphalt mixtures were evaluated: ...
Transportation Research Record: Journal of the Transportation Research Board, 2013
ABSTRACT One of the main requirements of designing perpetual pavements is to determine the endura... more ABSTRACT One of the main requirements of designing perpetual pavements is to determine the endurance limit of hot-mix asphalt (HMA). The endurance limit, as applied to HMA and flexible pavement design, is the strain or stress level below which the HMA would endure indefinite fatigue load repetitions and the pavement would not experience bottom-up fatigue cracking. The purpose of this study is to validate the endurance limit for HMA by using laboratory beam fatigue tests. A rational procedure was developed to determine the endurance limit of HMA attributable to healing that occurs during the rest periods between loading cycles. Relating healing to endurance limit makes this procedure unique compared with previous research projects that investigated these concepts separately. An extensive laboratory testing program was conducted according to AASHTO T 321-03 test procedure as a part of NCHRP Project 9-44A. Six factors that affected the fatigue response of HMA were evaluated: binder grade, binder content, air voids, test temperature, rest period, and applied strain. The endurance limit was determined when no accumulated damage occurred and indicated complete healing during the rest period after each load application. A threshold rest period of about 5 s for a load duration of 0.1 s—beyond which no more healing was gained—was obtained. HMA exhibits endurance limits ranging from 37 to 246 microstrains, depending on mixture properties and environmental conditions. The results of this study can be used to design perpetual pavements that can sustain a large number of loads if traffic volumes and vehicle weights are controlled.
ABSTRACT The properties of asphalt concrete are the result of many interdependent physical and ch... more ABSTRACT The properties of asphalt concrete are the result of many interdependent physical and chemical mechanisms occurring across multiple length scales. Admixtures such as hydrated lime (HL) and portland cement (PC) are known to affect the behaviors of asphalt concrete at the macroscale, but their contribution at other scales and influences on overall performance of the material are not well understood. This paper presents findings from a study to evaluate the potential for HL and PC for mitigating the effects of asphalt concrete aging with respect to modulus and fatigue resistance. The properties of interest were evaluated at multiple scales which involved binder, mastic, and mixture testing. Rheological analyses of aged and un-aged control, HL modified and PC modified mastics indicate that HL possesses greater potential to mitigate aging than PC. In mixture testing, the modulus results showed trends similar to that of mastics wherein the HL modified samples were the stiffest and also showed greater potential to mitigate aging. As expected, the relative increase in stiffness and relative potential to mitigate aging, averaged across temperatures, was found to be higher in mastics than the mixtures. The results from uniaxial fatigue test show that HL mixtures possess higher fatigue resistance when aged, thus less negative impacts from the oxidation process. Magnification of aging mitigation potential at the mastic scale and its direct correlation to fatigue behavior, explains why multiple scale evaluations can be useful in evaluating the true benefits of the admixtures.
This study was an investigation to identify whether the American Association of State Highway and... more This study was an investigation to identify whether the American Association of State Highway and Transportation Officials (AASHTO) T 283 Modified Lottman moisture susceptibility test can be successfully applied to assess moisture damage of the AR mixtures used in Arizona. A secondary objective of this study was to assess if the AASHTO TP 62-03 Dynamic Modulus E* laboratory test implemented in the pavement community is useful in assessing the susceptibility of conventional, HMA and AR mixtures. The research scope of work included conducting laboratory testing program on AR and conventional HMA mixes using AASHTO T 283 to determine the indirect tensile strength and Tensile Strength Ration (TSR). The AASHTO TP 62-03 Dynamic Modulus E* tests were then used to determine the percent retained stiffness, a term that was referred to as E* Stiffness Ratio (ESR). The TSR values were then compared to the ESR values for both conventional as well as AR mixes, and statistical analyses were conduc...
A recent Arizona State University study was conducted to evaluate two Warm Mix Asphalt (WMA) mixt... more A recent Arizona State University study was conducted to evaluate two Warm Mix Asphalt (WMA) mixturess. The evaluation included three laboratory tests on field cores as well as lab compacted specimens from an Arizona Department of Transportation (ADOT) project that involved two WMA test sections. The first section used a foamed-based WMA admixture, while the second section used a chemical-based WMA admixture. All laboratory testing were conducted at 70 °F (21 °C) and included; the dynamic modulus (E*), indirect tensile strength (IDT) and moisture damage evaluation using AASHTO T-283 test procedure. The testing plan of the foaming-based, chemical-based, and control sections of the study included field-cored specimens as well as laboratory specimens compacted at two different temperatures 270 °F (132 °C) and 310 °F (154 °C). On the foaming section of the study, field-stacked specimens showed statistically higher dynamic modulus compared to the lab-compacted specimens, meanwhile, the l...
Many well-constructed flexible pavements with a thick Hot Mix Asphalt (HMA) structure have been i... more Many well-constructed flexible pavements with a thick Hot Mix Asphalt (HMA) structure have been in service for 40 or more years without any evidence of fatigue cracking. This field experience suggests that an endurance limit, that is, a level of strain below which an asphalt concrete pavement will not exhibit fatigue cracks, is a valid concept for HMA mixtures. Several studies have been conducted to confirm the existence of an HMA fatigue endurance limit through an extensive program of laboratory testing, which further suggested that the endurance limit is influenced by HMA mixture and binder properties. NCHRP Project 9-44A was designed to extend the results and findings of previous studies with particular attention to the influence of asphalt binder and mixture properties on the endurance limit and to the relationship of the endurance limit to the phenomenon of healing hypothesized to occur in asphalt mixtures during the rest period between load applications in the laboratory and i...
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