Quantitative investigation of the shear bond performance between normal-strength and ultra-high-performance concrete under the influence of surface roughness

This study employs the spatial frequency content (SFC) method to quantify the roughness of the bonding interface between normal concrete (NC) and ultra-high-performance concrete (UHPC), and investigates its effect on interfacial bonding performance. Mechanical properties of both NC and UHPC were first tested. A 'Z'-shaped direct shear finite element model incorporating various rough interface profiles was then developed, and its accuracy was validated through experiments under identical conditions. The results demonstrate that the SFC method effectively characterizes the three-dimensional morphology and roughness of concrete interfaces. The finite element analysis closely matches the experimental results, confirming its reliability. Both numerical and experimental findings indicate that the optimal interface roughness ranges from 7.54 mm to 8.54 mm. While roughness beyond 8.54 mm can further enhance interfacial bonding strength, it does not significantly improve the overall load-bearing capacity of the composite structure.