Development of low-temperature performance specifications for asphalt mixtures using the bending beam rheometer

Thermal cracking due to stress at low temperature is a major factor in roadway degradation. The purpose of this study was to measure low-temperature response of asphalt mixtures from field cores, assess the practicality of using the bending beam rheometer (BBR) to test field mixtures, compare test results to observed field performance, determine whether a specification value can be obtained to evaluate low-temperature pavement performance, and determine if samples constructed in the laboratory using the same mix design reflect field performance. In this study, the BBR was used to test multiple field and laboratory asphalt mixtures. Field samples were obtained from cores located in the Salt Lake Valley in Utah. The response of field cores showed that although the same binder grade is used in the region, the resulting mixtures have significant differences in creep moduli and m-values. This indicates that binder testing alone might not be enough to control the material's creep modulus. The combination of BBR test results and field surveys indicates that both creep modulus and m-value play a significant role in low-temperature performance of asphalt pavements. Pavements with high creep moduli and low m-values are more susceptible to low-temperature thermal distress. From field observations, the field performance of each section was known; by plotting the test results of the field samples on a Black Space diagram, it can be observed that a thermal stress failure envelope might exist. However, more research will be necessary to further define a specific value for this specification.