From waste to performance evolution: Unveiling a critical aging stage in crumb rubber modified asphalt for sustainable pavement engineering

Understanding the long-term aging behavior of crumb rubber modified asphalt (CRMA) is crucial for sustainable pavement engineering and waste tire recycling. This study investigated the multiscale performance evolution of CRMA containing 20 wt% rubber powder during the early, standard long-term, and advanced aging stages by extending the PAV thermal oxidation aging test. CRMA samples aged from 0 h to 100 h in a pressure aging vessel (PAV) were characterized through frequency sweep, multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and atomic force microscopy (AFM). The results revealed a distinct transition region around PAV 40 h to PAV 60 h, marking a critical stage in rheological and microstructural evolution. Moderate aging enhanced high-temperature rutting resistance but reduced low-temperature flexibility, while deep aging led to pronounced hardening and brittleness. AFM results showed that the bee-like microstructure re-emerged and peaked at PAV 40 h, then vanished under over-aging, consistent with rheological degradation. This integrated macro–micro analysis identified PAV 40 h to PAV 60 h as a performance inflection point, providing insight into the multi-stage degradation mechanism of CRMA. The findings contribute to lifespan prediction, performance optimization, and high-value recycling of waste rubber, promoting greener and longer-lasting pavement materials.