In-situ tracking of multiscale fatigue degradation in the wearing course of asphalt pavement

Given that fatigue cracking poses a significant challenge for long-term asphalt pavements, this study investigated the multiscale fatigue properties in an asphalt wearing course using a large quantity of field cores collected annually from the Shenhai Freeway in Jiangsu Province, China from 2018 to 2023. The semi-circular bending (SCB), direct tension (DT) cyclic, and linear amplitude sweep (LAS) tests were conducted and the average annual attenuation of each resulting index was evaluated. The results indicated an accelerated decrease in the fracture energy and cracking resistance index with years in service, particularly in heavy traffic and dense-graded asphalt concrete sections. The LAS tests revealed a significant binder performance gradient with core depth that intensified over time, and the number of cycles to failure of the topmost layer exhibited a stronger correlation with the indices obtained by the DT than SCB tests. Next, the test results were validated against the field performance observed by visual inspection and quantified by the pavement condition index. Finally, the fatigue performance of the original wearing course five years after the application of an asphalt overlay was shown to be superior to that of the adjacent non-overlaid course with a 18.4 % average slower annual attenuation.