Interfacial damage mechanisms in hot-recycled asphalt mixtures: A molecular dynamics study considering the blending level between virgin and aged asphalt

The use of hot-recycled asphalt mixtures plays a key role in minimizing environmental pollution caused by waste asphalt and reducing energy consumption in the extraction of virgin materials, making it an essential strategy for promoting sustainable development in pavement engineering. Conventional hot recycling processes often yield incomplete blending between virgin and aged asphalt, leading to complex interfacial failure mechanisms at multiple potential interfaces. Current research has yet to fully elucidate these failure behaviors, significantly constraining the practical implementation of high-reclaimed asphalt pavement (RAP)-content mixtures. This study investigated the failure mechanisms of complex interfaces in hot-recycled asphalt mixtures under varying blending levels, combining molecular dynamics (MD) simulations with laboratory performance tests. Molecular models of asphalt with different aging levels and recycled asphalt with various blending levels were constructed. These models, along with interfacial systems involving acidic (quartz) and alkaline (calcite) aggregates, were used to analyze the variations in adhesion and cohesion energies. Experimental results showed that the adhesion strength at the aged asphalt-RAP aggregate interface increased significantly with higher aging levels of asphalt, especially when alkaline aggregates such as calcite were used, due to enhanced ionic and electrostatic interactions. Increasing the blending level between aged and virgin asphalt improved both the asphalt-aggregate adhesion and the asphalt-asphalt cohesion; however, this improvement was more pronounced when the aged asphalt had undergone severe oxidation. The failure location within the mixtures varied with both aggregate lithology and blending levels: in alkaline aggregate systems, interfacial failure primarily occurred between aged and virgin asphalt, while in acidic aggregate systems, the failure shifted from the recycled asphalt-aged asphalt interface to the recycled asphalt-virgin aggregate interface as the blending level increased. The evolution of moisture stability observed in laboratory tests closely matched the trends predicted by MD simulations, confirming the reliability of the simulation results. These findings provided the basis for performance optimization strategies: for alkaline aggregates, enhancing the blending level proved effective in improving mixture performance, while for acidic aggregates, the incorporation of anti-stripping agents or the use of more compatible aggregate types was recommended to ensure durability.