Studies on surface energy of asphalt and aggregate at different scales and bonding property of asphalt–aggregate system

Adhesion between asphalt and aggregate is rather essential to the service performance and durability of asphalt pavement. The surface energy of the asphalt binder and aggregate was proved effective to characterise the adhesive behaviour of asphalt–aggregate system, which had been studied with various measuring methods in recent years. However, most of these existing methods focus on the interfacial bonding characteristics at a macro-scale. The physical and mechanical properties of asphalt and aggregate at a micro-scale still needed to be clarified. In this study, Atomic Force Microscopy (AFM) was introduced to measure and calculate the surface energy of the asphalt and aggregate at nano-scale based on the classical Johnson–Kendall–Roberts and Fowkes theory. The surface energy of the asphalt and aggregate were also measured and determined with Sessile Drop method at millimetre scale. These test results were then related to the bonding property of the asphalt–aggregate system with a pull-off test. The aging was found to have a significant effect on the surface energy of the asphalt binder and thus affect the bonding performance between asphalt binder and aggregate. The measured surface energy of asphalt and aggregate by AFM method was found to represent the surface characteristics of materials and be able to characterise the bonding property between asphalt and aggregate.