Failure of the Asphalt–Aggregate Interface under Tensile Stress: Insight from Molecular Dynamics

Interfacial strength between asphalt binder and aggregate plays a vital role in maintaining the mechanical integrity of asphalt mixture. Given the lack of accurate testing instruments for the interaction of asphalt–aggregate interface, the adhesive interaction and failure evolution occurring at this interface has not been fully understood. In this study, molecular dynamics (MD) simulation was utilized to elucidate the mechanical and deformation behavior of the asphalt–aggregate interface under tensile stress from the atomic perspective. The interface system was constructed with a 12-component asphalt molecular model bonding on a silica substrate. This asphalt molecular model, combining the polymer consistent force field (PCFF) adopted to describe the inter-/intra-action of the system, was first validated. A stress-separation law of this interface can be obtained by tracing the atomic force during the tensile process. From this stress-separation law, the interfacial strength and work of adhesion can be derived. The influences of model size, loading rate, asphalt film thickness, and moisture were investigated. It was found that the interfacial failure type transfers from adhesive failure to cohesive failure as the loading rate decreases to a certain level. Moreover, the interfacial strength is highly associated with the failure type. The interfacial strength of the adhesive failure is about five times that of the cohesive failure, which demonstrates the traditional method of improving the adhesion performance of asphalt on aggregate through increasing its viscosity from the aspect of atomic modeling. Furthermore, the water molecules absorbed at the interface are crucial to the durability of the asphalt–aggregate system. This study provides deep insight into the interfacial failure of the asphalt–aggregate system and could serve as an initial step in multiscale modeling using bottom-up approaches for asphalt mixture.