Influence of constituents of recycled concrete aggregate on their grain-scale contact behavior considering 3D aggregate morphology and surface damage patterns

Recycled concrete aggregate (RCA) is a promising substitute for natural aggregates, and its applications in different geotechnical scenarios have received widespread attention. One of the critical factors that governs the mechanical response of RCA is the complex behavior at the contacts of the grains due to the mortar adhering to the aggregate surface. This work experimentally examined the interface behavior of different contact types, including aggregate to aggregate (A-A), aggregate to mortar (A-M), and mortar to mortar (M-M). The influence of local morphology and hardness on the interface behavior was analyzed through 3D scanning and microindentation tests. A novel scheme for calculating the local contact radius was developed based on the spatial point cloud. The results show that the inter-particle friction coefficient is correlated with the contact type, whereas the tangential stiffness is influenced, primarily, by the normal load. Based on cyclic normal contact tests, it was found that plastic deformations and plastic energy are dominant during the virgin cycle, however, elastic deformations prevail in the subsequent cycles. Simultaneously, contact types with higher hardness tend to accelerate the consumption of plastic energy, allowing elastic energy to surpass it. In terms of cyclic tangential contact behavior, significant scatter in the data was observed, which is associated with the heterogeneities in hardness, local morphology, and roughness, among other factors, resulting in relatively higher discrepancies in the data in the tangential direction.