Atomic mechanisms of separation failure at the asphalt-aggregate interface and its dependence on aging and rejuvenation: Insights from molecular dynamics simulations and DFT calculations

The microscopic interfacial properties between asphalt and aggregates determine the macroscopic cracking behaviors of asphalt mixtures. To provide guidance on durability enhancement for reclaimed asphalt pavement mixtures that are prone to cracking, the fracture resistance of asphalt-aggregate interface and its dependence on aging and rejuvenation was investigated by molecular dynamics simulations and density functional theory. The results revealed that although the separation resistance is influenced by the loading rate, temperature and aggregate composition, the separation of the virgin interface system usually occurs within the asphalt region. The aged interface also tends to separate inside the asphalt, but if the asphalt is severely aged, debonding occurs at the asphalt-aggregate interface because the cohesive strength within asphalt is stronger than the interfacial adhesion strength. The aged interface exhibits higher resistance to complete fracture than virgin interface under non-repetitive loading. However, the enhanced molecular polarity of aged asphalt reduces its molecular flow-ability, thus weakening the resistance of aged interface to fatigue failure. Rejuvenators containing both polar carboxyl groups and nonpolar alkyl groups function as intermediaries to promote the compatibility of aged asphalt molecules with virgin molecules, thus restoring the flowability and fatigue failure resistance of aged interface systems.