Developing an optional multiple repeated load test to evaluate permanent deformation of asphalt mixtures based on axle load spectrum

An optional multiple repeated load (OMRL) test, capable of simulating the axial load spectrum in real pavement, was developed to evaluate the rutting susceptibility of asphalt mixture. This new test was conducted at the temperature of 60 °C under multiple stresses determined by a simplified axle load spectrum considering the pavement management system (PMS). A pre-stage dynamic creep test was employed to determine the loading cycles of the first increment. Two kinds of asphalt mixtures were compared in the OMRL test with varying orders of multiple stresses and they were also tested in dynamic creep test under five different loading levels. As the test results show, loading sequences have a significant impact on the high-temperature performance of asphalt mixtures. The curve of permanent strain rate versus stress level could fit well with a power-law model in the dynamic creep test, and a similar result can be obtained by the OMRL test. However, the OMRL test shows higher efficiency than the traditional dynamic creep test. Besides, the secondary stage of the OMRL test fits a broken-line model since various stress levels are conducted on the specimen. The newly proposed lowest average strain rate (LASR) and multiple flow number (MFN) could evaluate the rutting resistance of asphalt mixtures under a more realistic loading condition. Overall, this OMRL test provides a better understanding of the rutting behavior of asphalt mixtures to improve the mix design and field performance.