Study on interfacial debonding between bitumen and aggregate based on micromechanical damage model

Macro-scale fractures of asphalt mixture usually exhibit multiple failure mechanisms including aggregate cracking, interfacial debonding between bitumen and aggregate, and binder tearing; however, damage modelling through conventional continuum mechanics fails to take into consideration the effects of the small-scale physical phenomena. This study aims to introduce a micromechanical damage model for a fundamental understanding of interfacial debonding in asphalt mixtures. The bilinear Cohesive Zone Model (CZM) was incorporated into the Mori-Tanaka model and the constitutive behaviour of asphalt mixtures was predicted. The results show that the interfacial debonding exhibit a significant dependency on aggregate size. A critical aggregate size was identified, above which the damage behaviour of asphalt mixtures changes from hardening to softening. The critical aggregate size increases withmortar modulus but decreases with softening interfacial stiffness, Poisson's ratio of the mortar and aggregate volume fraction. The interface strength and the fracture energy also have a significant effect on the fracture behaviour of asphalt mixtures. The strength of asphalt mixtures increases as the interface strength increases; it is independent of the fracture energy. Increased fracture energy can improve the fracture resistance of the asphalt mixture, while increased interface strength has an opposite effect.