Multiscale study on the deterioration of bitumen, bitumen-aggregate interface and asphalt mixture under the coupling effect of moisture and high temperature

The combined effects of moisture and high temperatures have emerged as a globally significant challenge, leading to the progressive degradation of asphalt pavements. This study aims to comprehensively investigate the deterioration of bitumen, bitumen-aggregate interface and asphalt mixture under the coupling effect of moisture and high temperature. For this purpose, the conventional physical tests, Fourier transform infrared radiation spectrometer, peeling test, Wilhelmy Plate Test, Marshall stability test, wheel track test and universal testing machine were conducted. The results showed that temperature and moisture significantly impacted the performance characteristics of bitumen, bitumen-aggregate interface, and asphalt mixtures. Among the three components, asphalt mixtures demonstrated the highest susceptibility to coupled conditions, exhibiting up to 53% performance variation. The bitumen-aggregate interface and bitumen showed relatively lower but still notable susceptibility. A particularly significant observation was the phase separation of bitumen under coupled conditions, manifesting as precipitated spheres at the container bottom and surface-floating films, which are identified as primary contributors to the degradation of bitumen-aggregate interfaces and asphalt mixtures. The statistical analyses further confirmed that the deterioration of asphalt mixtures was primarily attributed to changes in both the bitumen and bitumen-aggregate interface. Among all examined parameters, penetration and dynamic stability exhibited the most notable changes, while maximum flexural strain correlated strongly with other parameters, making these three key indicators for evaluating pavement durability.