A multi-scale adhesion mechanism analysis of asphalt mixtures containing epoxy resin at different aging conditions

Adhesion between asphalt binder and aggregate plays a critical role in the durability of asphalt mixtures and is strongly influenced by aging during the pavement service life. One possible strategy for improving asphalt mixture performance is epoxy resin modification; however, its influence must be evaluated across multiple length scales. In this study, a multi-scale framework is employed to investigate the adhesion-related behaviour of epoxy-modified asphalt mixtures under unaged, short-term and long-term aging conditions. At the macroscopic scale, adhesion performance is evaluated using the tensile strength ratio (TSR) obtained from the modified Lottman test. At the mesoscopic scale, degree of polarity derived from surface free energy analysis is used as a supporting physicochemical indicator. In contrast, at the microscopic scale, surface roughness measured by atomic force microscopy is used as a descriptive indicator of microstructural changes in the asphalt binder. The results of this study show that while asphalt mixtures without epoxy resin exhibit poor adhesion performance due to aging, increasing the epoxy resin content reduces this effect. In mixtures containing 20% epoxy resin, the adhesion performance of long-aged samples is even better than that of unaged samples. Furthermore, a strong correlation is observed between TSR and degree of polarity, while the correlation between TSR and surface roughness varies depending on the aging conditions and mixture type.