Fan Yin | Texas A&M University (original) (raw)

Papers by Fan Yin

Economic, environmental, and engineering benefits have led to the rapid implementation of Warm-Mi... more Economic, environmental, and engineering benefits have led to the rapid implementation of Warm-Mix Asphalt (WMA) across the world during the past decade. While WMA technologies have been successfully utilized as a paving material, standard mix design protocols remain under development. A study of the effect of laboratory conditioning protocols (prior to compaction) on the performance of HMA (Hot-Mix Asphalt) and WMA mixtures made with chemical additives, wax additives, or a foaming process was performed. Resilient Modulus (M R), Dynamic Shear Rheometer (DSR), and image analysis techniques were used to evaluate the properties of the extracted binders and mixtures conditioned with different protocols. Laboratory Mixed Laboratory Compacted (LMLC) specimens conditioned for 2 hours at 240°F (116°C) for WMA and 275°F (135°C) for HMA had stiffness similar to those of cores collected during the early life of field pavements. For off-site Plant Mixed Laboratory Compacted (PMLC) specimens, different conditioning protocols are recommended to simulate the stiffness of Plant Mixed Field Compacted (PMFC) cores at construction: reheat to 240°F (116°C) for WMA with additives and reheat to 275°F (135°C) for HMA and foamed WMA.

Economic, environmental, and engineering benefits promoted the rapid implementation of Warm-Mix A... more Economic, environmental, and engineering benefits promoted the rapid implementation of Warm-Mix Asphalt (WMA) across the world during the past decade. While WMA technologies have been successfully used as a paving material, concerns remain about the difference in performance between WMA and Hot-Mix Asphalt (HMA) due to changes in the mixture production process. Previous laboratory testing results indicate that WMA is oftentimes more susceptible to rutting and moisture damage as compared to HMA, and that this difference in performance is minimized with mixture aging. However, the prevalent concern of increased moisture susceptibility of WMA has not been observed in the field. The objectives of this study are to evaluate the differences in stiffness and moisture susceptibility between WMA and HMA with time (i.e., field and laboratory aging). Stiffness was measured with the Resilient Modulus (M R) test, while the Indirect Tensile (IDT) strength test and Hamburg Wheel Tracking Test (HWTT) were used to quantify moisture susceptibility. Test results show that field and laboratory aging significantly increase the stiffness and improve the moisture resistance of the mixtures, and equivalent or better performance can be achieved by WMA versus HMA after a summer of field aging or significant laboratory Long-Term Oven Aging (LTOA). The correlation between field aging and laboratory LTOA in terms of mixture performance was also determined as part of this study.

In the last two decades, changes in asphalt mixture components, production parameters, and plant ... more In the last two decades, changes in asphalt mixture components, production parameters, and plant design have occurred and raised the question of the validity of the current mix design procedures in adequately assessing the volumetric needs of asphalt mixtures and the physical characteristics required to meet performance expectations. A study of short-term aging of asphalt mixtures was performed considering the impacts of various asphalt mixture components and production parameters, including binder source, aggregate absorption, warm mix asphalt (WMA) technology, inclusion of recycled materials, plant type, and production temperature. In this study, the laboratory short-term oven aging (STOA) protocols of two hours at 135°C for hot mix asphalt (HMA) and two hours at 116°C for WMA were used to fabricate laboratory mixed and laboratory compacted (LMLC) specimens for volumetric analysis and performance evaluation by Resilient Modulus (M R) test, Dynamic Modulus (E*) test, and Hamburg Wheel Tracking Test (HWTT). The simulation of asphalt aging and absorption during plant production and construction by the laboratory STOA protocols was evaluated by comparing mixture volumetrics and laboratory test results with those for plant mixed and plant compacted (PMPC) specimens and cores at construction. In addition, the laboratory test results were used to identify those mixture components and production parameters with significant effects on the performance of short-term aged asphalt mixtures. Correlations for LMLC specimens and PMPC specimens and cores at construction in terms of mixture volumetrics and laboratory test results indicated that the laboratory STOA protocols of two hours at 135°C for HMA and two hours at 116°C for WMA were able to simulate the asphalt aging and absorption occurred during plant production and construction. According to the laboratory test results, among those factors investigated in this study; binder source, aggregate absorption, WMA technology, and inclusion of recycled materials had significant effects on the performance of short-term aged asphalt mixtures. However, no significant effects from mixture production temperature and plant type were observed.

In the United States, mechanical foaming is the most popular method for producing warm mix asphal... more In the United States, mechanical foaming is the most popular method for producing warm mix asphalt, which is the latest technology implemented to reduce the production temperature and/or enhance the compactability of asphalt mixtures. Three commonly used commercially available laboratory foamers to produce asphalt foams include the Wirtgen WLB 10S (Wirtgen foamer), the InstroTek Accufoamer (InstroTek foamer) and the Pavement Technology Inc. Foamer (PTI foamer). Though these foamers have been widely used in research studies and construction practice, it is still unknown whether they produce asphalt foams with the same quality and quantity. In this study, asphalt foaming characteristics produced by these three laboratory foamers were measured using a non-contact test set-up consisting of a laser device and a digital camera, and compared in terms of instantaneous volume expansion, foam stability and surface area evolution of foam bubbles. Additionally, the workability, coatability and mechanical performance of foamed mixtures prepared using these same laboratory foamers were compared against the conventional hot mix asphalt (HMA). Test results indicated that foamed asphalts produced by the Wirtgen foamer had the largest volume expansion and greatest foam stability, followed by those produced by the InstroTek foamer and the PTI foamer. The optimum foaming water content (W opt ) was determined for each laboratory foamer based on the workability and coatability results of the corresponding foamed mixtures. In addition, the performance evaluation of the foamed mixtures produced at W opt values indicated equivalent mixture stiffness but greater moisture susceptibility as compared to the conventional HMA.

Mechanical foaming is the most popular method for producing warm mix asphalt in the United States... more Mechanical foaming is the most popular method for producing warm mix asphalt in the United States; yet, a standard mix design procedure for foamed asphalt mixtures has not been established. Currently, the design of foamed asphalt mixtures consists of determining the optimum binder content by following a standard hot mix asphalt (HMA) design procedure and then estimating the foaming water content based on the foamer manufacturer's recommendation, engineering judgement, or previous experience. This practice fails to account for the effect of foaming on binder and mixture properties, and therefore may not ensure desirable foamed mixture performance. To overcome this shortcoming, additions to the standard mix design procedure were proposed in this study in order to accommodate foamed asphalt mixtures, which included optimisation of foaming water content and evaluation of foamed mixture performance. In addition, the proposed procedure was verified using materials procured from two field projects. The optimum foaming water content (W opt %) was first determined by comparing the workability results of foamed mixtures at various foaming water contents. Afterwards, the foamed mixture at W opt % was tested for coatability and performance evaluation, and all laboratory test parameters complied with established American Association of State Highway and Transportation Officials or agency specifications or were equivalent to or better than the control HMA test results. Therefore, the proposed foamed mix design procedure seemed a viable alternative for designing foamed mixtures with adequate pavement performance.

Asphalt Pavements, 2014

Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asp... more Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asphalt (WMA) during the past decade. While WMA technologies are generally performing well to date, development of standard mix design protocols continues and performance questions remain. This study evaluated laboratory conditioning protocols for WMA to simulate early life when they are more moisture susceptible and proposed 2 hours at 116°C for mix design and reheating to this temperature for quality assurance for all WMA technologies except foaming which requires reheating to 135°C. Next, WMA was shown to be more moisture susceptible as compared to Hot-Mix Asphalt in the early life based on a comprehensive analysis of three standard laboratory tests (wet and dry indirect tensile strengths and resilient modulus and their ratios and Hamburg Wheel Tracking Test stripping parameters) from four field projects that included nine WMA mixtures. Finally, an evaluation of performance evolution showed that WMA can overcome this vulnerability to moisture after a summer of aging and proposed 5 days oven aging at 85°C to capture this effect in the laboratory. Proposed conditioning protocols, aging protocols, and criteria for the tests utilized are provided for WMA mix design and analysis to preclude moisture susceptibility.

Transportation Research Record: Journal of the Transportation Research Board, 2015

Mechanical foaming has become the most popular method for producing warm-mix asphalt in the Unite... more Mechanical foaming has become the most popular method for producing warm-mix asphalt in the United States. The process of mixing cold water with hot binder results in volume expansion and subsequent viscosity reduction of the binder, which is likely to produce a better coating of the aggregates along with improved overall mixture workability. Although mechanical foaming has been widely used in recent years, questions persist regarding the effects that different amounts of water have on binder foaming characteristics and foamed mixture properties. This study developed a novel, noncontact method to measure the expansion and collapse of foamed binder during the foaming process and the evolution of the size and amount of foam bubbles over time. Two parameters were proposed for evaluating the effect of water content on binder foaming characteristics. In addition, the effect of water content on the foamed mixture properties of workability and performance was investigated. The test results indicated that the amount of water used in the foaming process had a significant effect on binder foaming characteristics and foamed mixture properties. The optimum foaming water content could be determined through evaluation of the workability of foamed asphalt mixtures produced at different foaming water contents. Compared with hot-mix asphalt mixtures, equivalent or better performance in laboratory tests was observed for plant-produced and laboratory-produced foamed mixtures at the optimum water content.

Journal of Materials in Civil Engineering, 2015

Warm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphal... more Warm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphalt concrete mixtures, allowing for savings in fuel consumption and extending haul distances and construction season. The reduced temperatures also provide a greener technology as emissions are lowered at the plant and the construction site. Engineering and environmental benefits promoted the rapid implementation of WMA technologies, but concerns remain regarding the difference in mixture performance of WMA versus hot-mix asphalt (HMA) because of the changes in the production process, specifically in terms of moisture susceptibility. This case study evaluates moisture susceptibility through the use of laboratory tests including the wet indirect tensile (IDT) strength test, the tensile strength ratio (TSR), and the Hamburg wheel tracking test (HWTT) analyzed with a novel methodology. The performance of two WMA technologies (Evotherm DAT and foaming) versus a control HMA is analyzed with and without antistripping additives and/or recycled materials after field and laboratory aging. Findings suggest that the WMA mixtures are more prone to moisture susceptibility in their early life as compared with HMA. The incorporation of recycled materials did not show a clear benefit for the WMA, whereas the inclusion of antistripping additives and aging significantly improved WMA in terms of moisture resistance, rendering mixtures with equivalent performance to HMA. individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561/05015002 /$25.00. © ASCE 05015002-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-3 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-4 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-5 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-7 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16.

Transportation Research Record: Journal of the Transportation Research Board, 2014

ABSTRACT

Asphalt Pavements, 2014

Foaming of asphalt binders has become the most popular method for producing Warm-Mix Asphalt (WMA... more Foaming of asphalt binders has become the most popular method for producing Warm-Mix Asphalt (WMA) in the United States. Mixing cold water and hot binder results in an expansion of the binder, a reduction in binder viscosity, and improved workability of the mixture and better coating of the aggregates by the foamed binder. The objectives of this study are to develop laboratory test methods to determine workability and coatability of asphalt mixtures and to validate the improved workability and coatability of foamed WMA as compared to Hot-Mix Asphalt (HMA). In the study, the maximum shear stress obtained during compaction using a Superpave Gyratory Compactor (SGC) is proposed as workability parameter. For mixture coatability evaluation, a testing procedure based on aggregate absorption is used and a coating parameter, coatability index, is proposed. Foamed WMA with different binder sources and grades and various water contents as well as control HMA are produced and evaluated in the study. Test results indicate that there is an optimum foaming water content that produces foamed WMA with the best workability and coatability characteristics when compared not only to other foamed WMA but also to control HMA.

Reports by Fan Yin

Economic, environmental, and engineering benefits have led to the rapid implementation of Warm-Mi... more Economic, environmental, and engineering benefits have led to the rapid implementation of Warm-Mix Asphalt (WMA) across the world during the past decade. While WMA technologies have been successfully utilized as a paving material, standard mix design protocols remain under development. A study of the effect of laboratory conditioning protocols (prior to compaction) on the performance of HMA (Hot-Mix Asphalt) and WMA mixtures made with chemical additives, wax additives, or a foaming process was performed. Resilient Modulus (M R), Dynamic Shear Rheometer (DSR), and image analysis techniques were used to evaluate the properties of the extracted binders and mixtures conditioned with different protocols. Laboratory Mixed Laboratory Compacted (LMLC) specimens conditioned for 2 hours at 240°F (116°C) for WMA and 275°F (135°C) for HMA had stiffness similar to those of cores collected during the early life of field pavements. For off-site Plant Mixed Laboratory Compacted (PMLC) specimens, different conditioning protocols are recommended to simulate the stiffness of Plant Mixed Field Compacted (PMFC) cores at construction: reheat to 240°F (116°C) for WMA with additives and reheat to 275°F (135°C) for HMA and foamed WMA.

Economic, environmental, and engineering benefits promoted the rapid implementation of Warm-Mix A... more Economic, environmental, and engineering benefits promoted the rapid implementation of Warm-Mix Asphalt (WMA) across the world during the past decade. While WMA technologies have been successfully used as a paving material, concerns remain about the difference in performance between WMA and Hot-Mix Asphalt (HMA) due to changes in the mixture production process. Previous laboratory testing results indicate that WMA is oftentimes more susceptible to rutting and moisture damage as compared to HMA, and that this difference in performance is minimized with mixture aging. However, the prevalent concern of increased moisture susceptibility of WMA has not been observed in the field. The objectives of this study are to evaluate the differences in stiffness and moisture susceptibility between WMA and HMA with time (i.e., field and laboratory aging). Stiffness was measured with the Resilient Modulus (M R) test, while the Indirect Tensile (IDT) strength test and Hamburg Wheel Tracking Test (HWTT) were used to quantify moisture susceptibility. Test results show that field and laboratory aging significantly increase the stiffness and improve the moisture resistance of the mixtures, and equivalent or better performance can be achieved by WMA versus HMA after a summer of field aging or significant laboratory Long-Term Oven Aging (LTOA). The correlation between field aging and laboratory LTOA in terms of mixture performance was also determined as part of this study.

In the last two decades, changes in asphalt mixture components, production parameters, and plant ... more In the last two decades, changes in asphalt mixture components, production parameters, and plant design have occurred and raised the question of the validity of the current mix design procedures in adequately assessing the volumetric needs of asphalt mixtures and the physical characteristics required to meet performance expectations. A study of short-term aging of asphalt mixtures was performed considering the impacts of various asphalt mixture components and production parameters, including binder source, aggregate absorption, warm mix asphalt (WMA) technology, inclusion of recycled materials, plant type, and production temperature. In this study, the laboratory short-term oven aging (STOA) protocols of two hours at 135°C for hot mix asphalt (HMA) and two hours at 116°C for WMA were used to fabricate laboratory mixed and laboratory compacted (LMLC) specimens for volumetric analysis and performance evaluation by Resilient Modulus (M R) test, Dynamic Modulus (E*) test, and Hamburg Wheel Tracking Test (HWTT). The simulation of asphalt aging and absorption during plant production and construction by the laboratory STOA protocols was evaluated by comparing mixture volumetrics and laboratory test results with those for plant mixed and plant compacted (PMPC) specimens and cores at construction. In addition, the laboratory test results were used to identify those mixture components and production parameters with significant effects on the performance of short-term aged asphalt mixtures. Correlations for LMLC specimens and PMPC specimens and cores at construction in terms of mixture volumetrics and laboratory test results indicated that the laboratory STOA protocols of two hours at 135°C for HMA and two hours at 116°C for WMA were able to simulate the asphalt aging and absorption occurred during plant production and construction. According to the laboratory test results, among those factors investigated in this study; binder source, aggregate absorption, WMA technology, and inclusion of recycled materials had significant effects on the performance of short-term aged asphalt mixtures. However, no significant effects from mixture production temperature and plant type were observed.

In the United States, mechanical foaming is the most popular method for producing warm mix asphal... more In the United States, mechanical foaming is the most popular method for producing warm mix asphalt, which is the latest technology implemented to reduce the production temperature and/or enhance the compactability of asphalt mixtures. Three commonly used commercially available laboratory foamers to produce asphalt foams include the Wirtgen WLB 10S (Wirtgen foamer), the InstroTek Accufoamer (InstroTek foamer) and the Pavement Technology Inc. Foamer (PTI foamer). Though these foamers have been widely used in research studies and construction practice, it is still unknown whether they produce asphalt foams with the same quality and quantity. In this study, asphalt foaming characteristics produced by these three laboratory foamers were measured using a non-contact test set-up consisting of a laser device and a digital camera, and compared in terms of instantaneous volume expansion, foam stability and surface area evolution of foam bubbles. Additionally, the workability, coatability and mechanical performance of foamed mixtures prepared using these same laboratory foamers were compared against the conventional hot mix asphalt (HMA). Test results indicated that foamed asphalts produced by the Wirtgen foamer had the largest volume expansion and greatest foam stability, followed by those produced by the InstroTek foamer and the PTI foamer. The optimum foaming water content (W opt ) was determined for each laboratory foamer based on the workability and coatability results of the corresponding foamed mixtures. In addition, the performance evaluation of the foamed mixtures produced at W opt values indicated equivalent mixture stiffness but greater moisture susceptibility as compared to the conventional HMA.

Mechanical foaming is the most popular method for producing warm mix asphalt in the United States... more Mechanical foaming is the most popular method for producing warm mix asphalt in the United States; yet, a standard mix design procedure for foamed asphalt mixtures has not been established. Currently, the design of foamed asphalt mixtures consists of determining the optimum binder content by following a standard hot mix asphalt (HMA) design procedure and then estimating the foaming water content based on the foamer manufacturer's recommendation, engineering judgement, or previous experience. This practice fails to account for the effect of foaming on binder and mixture properties, and therefore may not ensure desirable foamed mixture performance. To overcome this shortcoming, additions to the standard mix design procedure were proposed in this study in order to accommodate foamed asphalt mixtures, which included optimisation of foaming water content and evaluation of foamed mixture performance. In addition, the proposed procedure was verified using materials procured from two field projects. The optimum foaming water content (W opt %) was first determined by comparing the workability results of foamed mixtures at various foaming water contents. Afterwards, the foamed mixture at W opt % was tested for coatability and performance evaluation, and all laboratory test parameters complied with established American Association of State Highway and Transportation Officials or agency specifications or were equivalent to or better than the control HMA test results. Therefore, the proposed foamed mix design procedure seemed a viable alternative for designing foamed mixtures with adequate pavement performance.

Asphalt Pavements, 2014

Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asp... more Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asphalt (WMA) during the past decade. While WMA technologies are generally performing well to date, development of standard mix design protocols continues and performance questions remain. This study evaluated laboratory conditioning protocols for WMA to simulate early life when they are more moisture susceptible and proposed 2 hours at 116°C for mix design and reheating to this temperature for quality assurance for all WMA technologies except foaming which requires reheating to 135°C. Next, WMA was shown to be more moisture susceptible as compared to Hot-Mix Asphalt in the early life based on a comprehensive analysis of three standard laboratory tests (wet and dry indirect tensile strengths and resilient modulus and their ratios and Hamburg Wheel Tracking Test stripping parameters) from four field projects that included nine WMA mixtures. Finally, an evaluation of performance evolution showed that WMA can overcome this vulnerability to moisture after a summer of aging and proposed 5 days oven aging at 85°C to capture this effect in the laboratory. Proposed conditioning protocols, aging protocols, and criteria for the tests utilized are provided for WMA mix design and analysis to preclude moisture susceptibility.

Transportation Research Record: Journal of the Transportation Research Board, 2015

Mechanical foaming has become the most popular method for producing warm-mix asphalt in the Unite... more Mechanical foaming has become the most popular method for producing warm-mix asphalt in the United States. The process of mixing cold water with hot binder results in volume expansion and subsequent viscosity reduction of the binder, which is likely to produce a better coating of the aggregates along with improved overall mixture workability. Although mechanical foaming has been widely used in recent years, questions persist regarding the effects that different amounts of water have on binder foaming characteristics and foamed mixture properties. This study developed a novel, noncontact method to measure the expansion and collapse of foamed binder during the foaming process and the evolution of the size and amount of foam bubbles over time. Two parameters were proposed for evaluating the effect of water content on binder foaming characteristics. In addition, the effect of water content on the foamed mixture properties of workability and performance was investigated. The test results indicated that the amount of water used in the foaming process had a significant effect on binder foaming characteristics and foamed mixture properties. The optimum foaming water content could be determined through evaluation of the workability of foamed asphalt mixtures produced at different foaming water contents. Compared with hot-mix asphalt mixtures, equivalent or better performance in laboratory tests was observed for plant-produced and laboratory-produced foamed mixtures at the optimum water content.

Journal of Materials in Civil Engineering, 2015

Warm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphal... more Warm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphalt concrete mixtures, allowing for savings in fuel consumption and extending haul distances and construction season. The reduced temperatures also provide a greener technology as emissions are lowered at the plant and the construction site. Engineering and environmental benefits promoted the rapid implementation of WMA technologies, but concerns remain regarding the difference in mixture performance of WMA versus hot-mix asphalt (HMA) because of the changes in the production process, specifically in terms of moisture susceptibility. This case study evaluates moisture susceptibility through the use of laboratory tests including the wet indirect tensile (IDT) strength test, the tensile strength ratio (TSR), and the Hamburg wheel tracking test (HWTT) analyzed with a novel methodology. The performance of two WMA technologies (Evotherm DAT and foaming) versus a control HMA is analyzed with and without antistripping additives and/or recycled materials after field and laboratory aging. Findings suggest that the WMA mixtures are more prone to moisture susceptibility in their early life as compared with HMA. The incorporation of recycled materials did not show a clear benefit for the WMA, whereas the inclusion of antistripping additives and aging significantly improved WMA in terms of moisture resistance, rendering mixtures with equivalent performance to HMA. individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561/05015002 /$25.00. © ASCE 05015002-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-3 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-4 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-5 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 05015002-7 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 2016, 28(2): 05015002 Downloaded from ascelibrary.org by Texas A&M University on 04/04/16.

Transportation Research Record: Journal of the Transportation Research Board, 2014

ABSTRACT

Asphalt Pavements, 2014

Foaming of asphalt binders has become the most popular method for producing Warm-Mix Asphalt (WMA... more Foaming of asphalt binders has become the most popular method for producing Warm-Mix Asphalt (WMA) in the United States. Mixing cold water and hot binder results in an expansion of the binder, a reduction in binder viscosity, and improved workability of the mixture and better coating of the aggregates by the foamed binder. The objectives of this study are to develop laboratory test methods to determine workability and coatability of asphalt mixtures and to validate the improved workability and coatability of foamed WMA as compared to Hot-Mix Asphalt (HMA). In the study, the maximum shear stress obtained during compaction using a Superpave Gyratory Compactor (SGC) is proposed as workability parameter. For mixture coatability evaluation, a testing procedure based on aggregate absorption is used and a coating parameter, coatability index, is proposed. Foamed WMA with different binder sources and grades and various water contents as well as control HMA are produced and evaluated in the study. Test results indicate that there is an optimum foaming water content that produces foamed WMA with the best workability and coatability characteristics when compared not only to other foamed WMA but also to control HMA.