Microcosmic mechanism of asphalt-aggregate interface adhesion failure under freeze-thaw cycles based on molecular dynamics

Abstract

ABSTRACT In order to investigate the micro-mechanisms of adhesive failure at the asphalt-aggregate interface under freeze-thaw cycling, this study presents a novel model for freeze-thaw cycling of asphalt mixtures constructed using molecular dynamics. The model is employed to explore the micro-mechanisms of adhesive failure between asphalt and aggregate surfaces under freeze-thaw cycling conditions. Utilising the four-component model of asphalt, asphalt molecules were constructed, with silicon dioxide and calcium carbonate chosen to represent acidic and alkaline aggregates, respectively. Subsequently, an asphalt-aggregate-water freeze-thaw cycling model was developed. Building upon this foundation, the variations in interface interactions between asphalt and the two types of minerals were analysed under the same freeze-thaw cycling conditions but differing freeze-thaw cycle counts. This analysis was conducted through the examination of Radial Distribution Function (RDF), water molecule coordination numbers, and hydrogen bond quantities at the interfaces between asphalt and the two mineral types. The research findings indicate that acidic aggregates exhibit a greater affinity for water molecules compared to alkaline aggregates. Hydrogen bond interactions exist between aggregates and water molecules, with the hydrogen bond energy being greater than the interactions between asphalt molecules and aggregate surfaces. The cohesive energy decreases with an increasing number of freeze-thaw cycles, leading to a gradual reduction in asphalt viscosity and facilitating the detachment of asphalt from the aggregate surface. Consequently, acidic aggregates tend to absorb water molecules more readily, and water can lower the viscosity of asphalt molecules, ultimately resulting in the macroscopic delamination of asphalt from the aggregate surface. These research outcomes provide valuable theoretical guidance for a deeper exploration of the adhesive failure mechanisms in asphalt-aggregate interactions.