Cohesive and adhesive bonding within the asphalt-aggregate system are directly related to the surface energy of the asphalt. The thermodynamic changes in the surface energy of adhesion and cohesion are related to the de-bonding of the interface between asphalt and aggregate and to cracks that may occur within the mastic, respectively. However, it is also true that thermodynamic changes in the surface energy are required to heal a fracture between the surfaces of the asphalt and the aggregate or within the mastic. The methodology and testing protocol for measuring the surface energy of asphalt are presented. Both the surface energy of dewetting (fracture) and the surface energy of wetting (healing) can be obtained from the contact angle measurement with the Wilhelmy plate method. Ten asphalts were tested; surface energies varied substantially as a function of asphalt composition and the level of aging to which the asphalt was subjected. By using thermodynamic theory, the adhesion and cohesion bonding energy within the asphalt-aggregate systems were further analyzed. This analysis has the potential to select the most compatible asphalt-aggregate combination for mixtures. The surface energy is also a very important parameter in the fatigue and healing analysis of the asphalt pavement.
Abstract