Study on the shear failure characteristics of RAC push-off specimens with UHPC shear keys

Abstract This study investigates the damage modes and cracks development patterns of recycled aggregate concrete (RAC) and ultra-high-performance concrete (UHPC) push-off specimens under direct shear. The experimental results reveal three distinct damage modes for specimens with varying numbers of shear keys: failure along the RAC-UHPC interface, failure along the interface on one side and around the interface on the other, and failure completely around the interface. Specimens with shear keys (R-U-1K, R-U-2K, and R-U-3K) demonstrated increases in ultimate shear stresses of 13.6%, 6.4%, and 18.2%, compared to the control specimen (R-U-m). Digital image correlation (DIC) analysis demonstrated that specimens with shear keys predominantly exhibited stress concentration in horizontal or vertical directions, leading to tensile-shear damage. A finite element model (FEM) was used to simulate and analyze the behavior of the push-off specimens, with results aligning well with the experimental findings. The findings confirm the feasibility of employing UHPC shear keys to increase bearing capacity of RAC-UHPC composite members. These insights are valuable for optimizing the design and promoting the high-value engineering application of RAC in composite structures.