Investigation of the Effects of Adsorbed Water on Adhesion Energy and Nanostructure of Asphalt and Aggregate Surfaces Based on Molecular Dynamics Simulation

The purpose of this study was to investigate the effect of aggregate surface adsorbed water on the adhesive capacity and nanostructure of asphalt-aggregate interfaces at the atomic scale. Molecular dynamics (MD) simulation was performed to measure and analyze the molecular interactions of asphalt binder with calcite and silica. Radial distribution function (RDF) and relative concentration (RC) were applied to characterizing the concentrations and distributions of asphalt components on aggregate surfaces. In addition, debonding energy and adhesion energy were employed to calculate the variations of interface adhesion energy of the asphalt-aggregate system under different conditions. The obtained results illustrated that the water molecules adsorbed onto the surface of weakly alkaline aggregates inhibited the concentration and distribution of asphalt components near the aggregate surface, decreased adhesion energy between asphalt and aggregates, and changed asphalt nanostructure. Especially, when external free water intruded into the interface of the asphalt-calcite system, the adsorbed water interacted with free water and seriously declined the water damage resistance of the asphalt mixture with limestone as an aggregate and decreased the durability of the mixtures. The water adsorbed onto the surface of the acid aggregate negatively affected the asphalt-silica interface system and slightly reduced the water damage resistance of the asphalt mixture.