Application of Sessile Drop Method to Determine Surface Free Energy of Asphalt and Aggregate

Surface free energy is an important parameter to determine the work of adhesion between the asphalt binder and the aggregate, which is related to the moisture damage of asphalt mixture. In this study, the sessile drop technique was performed to obtain the contact angle between asphalt/aggregate and different probe liquids. The surface free energies of asphalt and aggregate were characterized on the basis of the Owens-Wendt's theory. It was found that the sessile drop technique is a convenient way to determine the static contact angle. A test procedure was developed to offer a clear method to prepare the sample and measure the contact angle. The surface free energy of aggregate determined in this study was found to be smaller than that measured in other techniques because of equilibrium spreading pressure. The work of adhesion calculated from surface free energy can be utilized to choose the best combination of asphalt and aggregate, which can work as a reference in the selection of materials. Meanwhile, it was found that for the same aggregate, the pull-off strength and the work of adhesion of each asphalt-aggregate have the same trend of ranking.