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This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture performance tests and investigated the possibility of estimating the low-temperature fracture properties of aged mixtures by using a nonlinear ultrasonic approach. Asphalt mixture samples, oven aged for 12, 24, 28, 32, and 36 h at 135°C, were compacted, made into test specimens, and evaluated by using a noncollinear wave-mixing approach. In addition, the embrittlement temperature and fracture energy of the replicate samples were assessed by using the acoustic emission test and the disk-shaped compact tension test. Comparison of results from the three testing methods clearly showed similar trends. This finding suggests that the fracture properties of mixtures can be estimated by using the noncollinear ultrasonic wave-mixing approach, which is a nondestructive method which does not require core extraction in the field.

This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture performance tests and investigated the possibility of estimating the low-temperature fracture properties of aged mixtures by using a nonlinear ultrasonic approach. Asphalt mixture samples, oven aged for 12, 24, 28, 32, and 36 h at 135°C, were compacted, made into test specimens, and evaluated by using a noncollinear wave-mixing approach. In addition, the embrittlement temperature and fracture energy of the replicate samples were assessed by using the acoustic emission test and the disk-shaped compact tension test. Comparison of results from the three testing methods clearly showed similar trends. This finding suggests that the fracture properties of mixtures can be estimated by using the noncollinear ultrasonic wave-mixing approach, which is a nondestructive method which does not require core extraction in the field.

The sustainability movement in paving materials has led to the increased use of reclaimed asphalt pavement (RAP). New developments in this area in the recent past include the use of biomodified asphalt binders (BMBs) such as those containing bio-oils derived from swine manure. The study reported in this paper examined the low-temperature properties of RAP and virgin BMB mixtures to determine if these mixtures exhibited better low-temperature performance than conventional hot-mix asphalt (HMA). Disk-shaped compact tension [DC(T)], Superpave® indirect tension (IDT), and acoustic emission (AE) tests were employed to characterize low-temperature properties of the asphalt mixtures. BMB mixtures exhibited higher DC(T) fracture energies than HMA at all RAP levels. In addition, BMB mixture fracture energy displayed a reduced dependence on RAP content. The difference in average fracture energy between BMB and HMA mixtures increased with higher RAP contents. Furthermore, BMB mixtures displayed consistently higher creep compliance, which indicated that these mixtures could alleviate thermal stresses more easily than HMA. A recently developed AE testing procedure evaluated the effects of BMB as well as RAP in the mixtures. The overall trends identified through AE testing were consistent with the findings from the DC(T) and IDT tests. In addition, AE results suggested a fundamental change in the behavior of the BMB RAP mixture relative to the HMA RAP mixture (i.e., rejuvenating effect). In general, it was observed that BMB RAP mixtures exhibited low-temperature cracking behavior superior to that of HMA mixtures.

The sustainability movement in paving materials has led to the increased use of reclaimed asphalt pavement (RAP). New developments in this area in the recent past include the use of biomodified asphalt binders (BMBs) such as those containing bio-oils derived from swine manure. The study reported in this paper examined the low-temperature properties of RAP and virgin BMB mixtures to determine if these mixtures exhibited better low-temperature performance than conventional hot-mix asphalt (HMA). Disk-shaped compact tension [DC(T)], Superpave®indirect tension (IDT), and acoustic emission (AE) tests were employed to characterize low-temperature properties of the asphalt mixtures. BMB mixtures exhibited higher DC(T) fracture energies than HMA at all RAP levels. In addition, BMB mixture fracture energy displayed a reduced dependence on RAP content. The difference in average fracture energy between BMB and HMA mixtures increased with higher RAP contents. Furthermore, BMB mixtures displayed consistently higher creep compliance, which indicated that these mixtures could alleviate thermal stresses more easily than HMA. A recently developed AE testing procedure evaluated the effects of BMB as well as RAP in the mixtures. The overall trends identified through AE testing were consistent with the findings from the DC(T) and IDT tests. In addition, AE results suggested a fundamental change in the behavior of the BMB RAP mixture relative to the HMA RAP mixture (i.e., rejuvenating effect). In general, it was observed that BMB RAP mixtures exhibited low-temperature cracking behavior superior to that of HMA mixtures.

In the field of asphalt concrete, the use of warm-mix asphalt (WMA) has become one of the most popular methods of meeting sustainability demands. Researchers have determined that WMA use can lead to reductions in fuel consumption and emissions. Early literature hypothesized that an additional benefit, regardless of the WMA additive or process used, was decreased susceptibility to thermal cracking. The current study examined this hypothesis through laboratory testing of four WMA mixtures produced at a reduced production temperature and a reference hot-mix asphalt (HMA) mixture. The disk-shaped compact tension, indirect tension, and acoustic emission tests were used to characterize the low-temperature properties of the mixture. The fracture energy results of the disk-shaped compact tension test showed that the chemical additives improved fracture energy in comparison with HMA and that the organic and foaming additives reduced fracture energy. The indirect tension creep compliance test produced similar results, in which the two chemical additive-modified WMA systems increased mixture creep compliance, while the other two systems did not significantly alter creep compliance as compared with the control HMA mixture. Acoustic emission testing provided further information regarding the low-temperature behavior of WMA mixtures. The foaming additive displayed an embrittlement temperature similar to that of HMA, whereas the organic additive increased the embrittlement temperature. The two chemical additive-modified mixtures produced differing embrittlement temperatures. It was concluded that resistance to thermal cracking was not ensured by producing WMA mixtures at lower temperatures. Therefore, performance testing is critical to evaluating WMA technologies in locations susceptible to low temperatures.

In the field of asphalt concrete, the use of warm-mix asphalt (WMA) has become one of the most popular methods of meeting sustainability demands. Researchers have determined that WMA use can lead to reductions in fuel consumption and emissions. Early literature hypothesized that an additional benefit, regardless of the WMA additive or process used, was decreased susceptibility to thermal cracking. The current study examined this hypothesis through laboratory testing of four WMA mixtures produced at a reduced production temperature and a reference hot-mix asphalt (HMA) mixture. The disk-shaped compact tension, indirect tension, and acoustic emission tests were used to characterize the low-temperature properties of the mixture. The fracture energy results of the disk-shaped compact tension test showed that the chemical additives improved fracture energy in comparison with HMA and that the organic and foaming additives reduced fracture energy. The indirect tension creep compliance test produced similar results, in which the two chemical additive–modified WMA systems increased mixture creep compliance, while the other two systems did not significantly alter creep compliance as compared with the control HMA mixture. Acoustic emission testing provided further information regarding the low-temperature behavior of WMA mixtures. The foaming additive displayed an embrittlement temperature similar to that of HMA, whereas the organic additive increased the embrittlement temperature. The two chemical additive–modified mixtures produced differing embrittlement temperatures. It was concluded that resistance to thermal cracking was not ensured by producing WMA mixtures at lower temperatures. Therefore, performance testing is critical to evaluating WMA technologies in locations susceptible to low temperatures.

Significant increases in the cost of asphalt paving and increased awareness of the need for sustainable infrastructure in recent years have in turn increased the use of recycled asphalt pavement (RAP) in the manufacture of hot-mix asphalt (HMA). The use of RAP reduces the overall cost of HMA and provides significant environmental benefits. Experience has shown, however, that the addition of RAP to HMA can have a negative effect on the low-temperature fracture characteristics of the pavement. The purpose of this study was to determine the effects of RAP amounts on the low-temperature cracking performance of asphalt mixtures. Different percentages of RAP material, ranging from 0% to 50%, were studied. The embrittlement temperature of mixtures was determined with the use of an acoustic emissions technique. The disk-shaped compact tension [DC(T)] test was used to determine the fracture energy of asphalt mixtures. DC(T) fracture tests were conducted on two control mixtures with no RAP and mixtures that contained 10%, 20%, 30%, 40%, and 50% RAP. Both control and RAP mixtures were manufactured with PG 64-22 and PG 58-28 as the virgin binders, which brought the total number of mixtures tested to 12. In addition to DC(T) fracture testing, indirect tensile testing was conducted on HMA specimens that contained 20% and 40% RAP. Test results clearly indicated the effects of the presence of RAP materials on the low-temperature performance of mixtures. This study demonstrates the benefit of performing fracture tests before RAP is added to the asphalt mixture, and it demonstrates the use of an acoustic emissions-based testing procedure to screen mixtures susceptible to cracking at low temperatures.

Significant increases in the cost of asphalt paving and increased awareness of the need for sustainable infrastructure in recent years have in turn increased the use of recycled asphalt pavement (RAP) in the manufacture of hot-mix asphalt (HMA). The use of RAP reduces the overall cost of HMA and provides significant environmental benefits. Experience has shown, however, that the addition of RAP to HMA can have a negative effect on the low-temperature fracture characteristics of the pavement. The purpose of this study was to determine the effects of RAP amounts on the low-temperature cracking performance of asphalt mixtures. Different percentages of RAP material, ranging from 0% to 50%, were studied. The embrittlement temperature of mixtures was determined with the use of an acoustic emissions technique. The disk-shaped compact tension [DC(T)] test was used to determine the fracture energy of asphalt mixtures. DC(T) fracture tests were conducted on two control mixtures with no RAP and mixtures that contained 10%, 20%, 30%, 40%, and 50% RAP. Both control and RAP mixtures were manufactured with PG 64-22 and PG 58-28 as the virgin binders, which brought the total number of mixtures tested to 12. In addition to DC(T) fracture testing, indirect tensile testing was conducted on HMA specimens that contained 20% and 40% RAP. Test results clearly indicated the effects of the presence of RAP materials on the low-temperature performance of mixtures. This study demonstrates the benefit of performing fracture tests before RAP is added to the asphalt mixture, and it demonstrates the use of an acoustic emissions-based testing procedure to screen mixtures susceptible to cracking at low temperatures.