Adhesion Mechanisms Between Rubber-Modified Asphalts and Aggregates Under Aging Conditions: A Molecular Dynamics Study

The interfacial adhesion between asphalt binders and aggregates is one of the critical factors influencing the mechanical performance and durability of asphalt mixtures, particularly under aging conditions. In this study, molecular dynamics (MD) simulations were conducted to investigate the adhesion mechanisms of styrene–butadiene–styrene (SBS)-modified asphalt, reclaimed crumb rubber (RCR)-modified asphalt, and RCR/SBS composite-modified asphalt with limestone aggregate. The simulated densities and glass transition temperatures of the asphalt models closely matched experimental values, with deviations within 2.5% and 20K, respectively, confirming the reliability of the modeling approach. The results showed that short-term aging significantly enhanced the cohesive energy of the asphalt and its adhesion energy to aggregates, primarily because of the formation of polar functional groups that strengthened electrostatic interactions at the interface. Among all systems, the RCR/SBS composite-modified asphalt exhibited the greatest improvement in adhesion energy, increasing from 284.57 to 378.17 kcal/mol (32.9% increase), surpassing that of the SBS (26.4%) and RCR (19.1%) modified systems. The simulations further revealed a shift in the dominant adhesion mechanism from Van der Waals forces in the unaged state to electrostatic interactions after aging, accompanied by reduced adsorption distances and higher interfacial atomic densities. These findings provide molecular-level insight into how modifier type and oxidative aging influence asphalt–aggregate interactions, offering theoretical support for the design of more durable and aging-resistant asphalt materials.