Gradient degradation and interfacial failure mechanisms of asphalt binder under multi-factor coupling in high-altitude region

Asphalt pavements in high-altitude regions are subjected to intense ultraviolet radiation, freeze–thaw cycles, and dynamic water scouring, which accelerate asphalt binder deterioration. This study developed laboratory protocols to simulate coupled UV aging and moisture damage under these harsh conditions. The aging mechanisms were investigated using dynamic shear rheometer, bending beam rheometer, binder bond strength, Fourier transform infrared spectroscopy, and scanning electron microscopy. Results showed that both static and dynamic water environments accelerated UV-induced oxidation and modifier degradation, while F–T cycles promoted chemical aging by generating microcracks and additional reactive surfaces. Rheological analysis indicated that F–T cycling intensified UV-induced hardening and enhanced binder elasticity and elastic recovery. In contrast, moisture exposure mitigated aging severity. Dynamic water scouring introduced a continuous aging–peeling process that reduced the accumulation of oxidation products, resulting in smaller improvements in rutting resistance and elastic recovery than static immersion. Fatigue resistance decreased under all coupled aging conditions, with F–T cycles causing the greatest reduction. Furthermore, aging-induced hardening and increased surface roughness enhanced asphalt–aggregate bonding, while dynamic water scouring accelerated the transition from adhesive to cohesive failure. These findings provide insights into the degradation mechanisms of asphalt binders under multi-factor coupling.