Characterization of permanent deformation performance of asphalt mixture by multi-sequenced repeated load test

In an attempt to characterize the permanent deformation behavior of hot mix asphalt (HMA) under a more realistic loading condition, this study developed a multi-sequenced repeated load (MSRL) test. Comparing to conventional repeated load (RL) test, there are three characteristics for this new test. First, the loading scheme, containing a pre-loading sequence with stress level of 0.7 MPa and other 25 sequences involving stress levels from 0.6 MPa to 1.0 MPa, was self-defined by the test design function of UTM-25. Second, the number of repeated loading in each sequence was fixed, with 500 times in pre-loading and 50 times in every other sequence. Third, two new indicators, including compound average strain rate (CASR) and compound creep stiffness modulus (CCSM), were proposed to evaluate the rutting-resistant property of HMA. Both MSRL test at different loading orders and RL test under stress levels of 0.7 MPa and 1.0 MPa were conducted on three types of mixtures with two binders at temperature of 60 °C, respectively. The findings indicate that the effects of loading order are insignificant on the permanent deformation of HMA in secondary stage. Besides, average strain rate (ASR) has a nonlinear growth as stress level increases. Based on MSRL test results, coefficient of variance for new indicators is satisfactory. Through analysis of variance, it is also found that new indicators, with much reduced levels of confidence, have much better potentials to statistically differentiate mixtures with different SBS modified binders than conventional ones like flow number (FN), FN index and so on.