Evaluating the rutting and moisture resistance of asphalt mixes using the IDT-HT and HWTT

The Hamburg wheel tracking test (HWTT) has been used by many state transportation agencies to evaluate both rutting resistance and moisture susceptibility. The current rutting parameter based on total rut depth (TRD) does not separate between rutting caused by plastic deformation and that caused by stripping. An alternative parameter, i.e. corrected rut depth (CRD), has been suggested to evaluate rutting that occurs solely due to plastic deformation without considering the effect of stripping. In this study, thirty-three plant-produced mixes were sampled from different producers in Oklahoma, representing a wide range of materials and mix types. The plant-produced mixes were tested using HWTT at 50°C and analyzed to determine their TRD and CRD. Furthermore, the potential of using the indirect tensile test at high temperature (IDT-HT) for acceptance during production was evaluated using a test temperature of 50°C. From the results, it was shown that the CRD provides a better measure of rutting compared to the TRD. A rutting criterion was proposed using a maximum CRD of 6 mm at 10,000, 15,000, and 20,000 wheel passes for mixes with PG64-22, PG70-28, and PG76-28, respectively. A moisture susceptibility criterion using a minimum stripping number (SN) of 2000 passes was suggested, which approximately coincides with a minimum stripping inflection point (SIP) of 10,000 passes. Using the IDT-HT, a minimum strength of 240 kPa (35 psi) was proposed as an acceptance threshold during production.