Relationship Between Chemical Aging Indices and Surface Energy Parameters of Asphalt Binder

Abstract: An asphalt binder’s surface free energy (SFE) is a thermodynamic property that can be used to describe its bonding characteristics to aggregates in an asphalt mix. As asphalt binder undergoes oxidative aging during its service life, it experiences alterations in its chemical composition, which can affect its cohesive and adhesive bonds. Therefore, this study was undertaken to determine the changes in asphalt binder’s adhesion and debonding potential due to different aging scenarios. For this purpose, a PG 58-28 asphalt binder was short-term aged in a rolling thin-film oven (RTFO) and long-term aged in a pressure-aging vessel (PAV) for 20, 40, and 60 hours. Then, the contact angles of the asphalt binders (unaged, RTFO-aged, and PAV-aged for 20, 40, and 60 hours) with different probe liquids were measured by conducting the Sessile drop test, and their SFE components were determined. The changes in the chemical composition of the asphalt binder due to aging were evaluated by performing Fourier transform infrared (FTIR) spectroscopy and observing the oxidation products, namely carbonyl (C=O) and sulfoxide (S=O) functional groups. In addition, observed changes in the functional groups in an asphalt binder and their effect on the measured SFE parameters and moisture-induced damage due to aging were presented and discussed. The findings of this study are expected to enhance our understanding of the effect of aging on the bonding characteristics of asphalt binders to aggregates through a chemical- and thermodynamic-based approach.