Analysis of the Mechanisms of Microscopic Diffusion and Adhesion at the Interface Between High-Content Polymer-Modified Asphalt and Aggregates

This paper aims to analyse the mechanisms of microscopic diffusion and adhesion at the interface between polymer-modified asphalt and aggregate at high blending ratios. Using molecular dynamics simulations, a model of the polymer-modified asphalt–aggregate interface was developed. The study systematically investigated the effects of three types of modifiers—SBS, SBR and PE—on the wetting, diffusion and adhesion behaviour at the asphalt interface within a content range of 2.5% to 10% and under various temperature conditions. The results indicate that an increase in modifier content inhibits the migration of light fractions towards the interface, leading to weakened interfacial diffusion and non-uniform wetting under high-temperature conditions. In contrast, the SBS and SBR systems are more sensitive to changes in temperature and modifier content, while the PE system exhibits a relatively weaker diffusion attenuation effect. The interfacial adhesion results further indicate that the adhesion energy between modified asphalt and aggregate is higher at low temperatures and is primarily governed by van der Waals forces; as the modifier content increases, interfacial adhesion at low temperatures is enhanced, but construction and coating performance at high temperatures are somewhat affected. This study elucidates the microstructural diffusion and adhesion mechanisms of high-content polymer-modified asphalt under cold-climate conditions, providing a theoretical basis for the selection of modified asphalt materials and the optimisation of mix designs in low-temperature regions.