Shear performance of new-to-old concrete interface based on various surface preparation techniques and roughness

In reinforced concrete structures, the interface between old and new concrete is commonplace in precast splices, repairs, and construction joints, and is vital for structural integrity. While extensive research has been conducted on the mechanical bonding properties of interfaces between new and old concrete, there remains a notable gap in understanding the shear behavior under various interfacial treatments. To investigate the influence of interface preparation methods and surface roughness on the shear performance of new-to-old concrete interface, direct shear tests were conducted on Z-shaped specimens. The surface roughness of the initially cast specimens was measured using 3D laser scanning, and the interface morphology was observed by scanning electron microscopy. A comprehensive analysis of comparison between calculated and experimental shear strength values was conducted on 243 sets of direct shear test data. Results revealed that the surface roughness of the specimens ranged from 0.13–3.69 mm, with voids of 0.5–10 μm width present in the bond interfaces. Two failure modes, namely cohesion and adhesion, were identified in the aggregates on the bond interfaces. Within a specific range, the shear strength of bond interfaces increased with an increase in surface roughness. Additionally, bond interfaces with the same roughness but different surface process methods exhibited varying shear bearing capacities. Furthermore, the formula for calculating the shear strength of bond interfaces based on different surface preparation processes and segmented roughness was developed.