Bonding Performance of Concrete Structure Strengthened with Ultra-High-Performance Concrete Under Bending Experiment

Ultra-high-performance concrete is widely used in bridge strengthening to improve mechanical performance and bridge durability. Interfacial bonding performance is a key factor in ensuring the effectiveness of ultra-high-performance concrete strengthening. The bending test of the UHPC-NC composite structure was carried out in this article. The effects of groove treatment type and epoxy resin bonding were considered to discuss the damage modes, load-deflection relationships, and strengths. The interfacial tensile strength of the UHPC-NC composite structure and the distribution pattern of cracks were clarified. The results of the test showed that (a) only 22.2% of the groove-treated specimens failed due to bonding surface failure, indicating that the UHPC-NC bonding surface has a high degree of reliability; (b) the strength of specimens with an epoxy adhesive interface was the lowest. It was only 21% higher than the pure normal concrete specimen, and the effective synergistic force of UHPC-NC cannot be achieved; (c) the specimens treated with a positive trapezoidal keyway exhibited the highest strength, with an increase of approximately 200% compared to the pure normal concrete specimens. The strength of bending specimens with right-angled and inverted trapezoidal grooves increased by approximately 100% compared with pure normal concrete specimens. Based on the established three-dimensional numerical model and the analysis of test results under economic and safe conditions, the positive trapezoidal keyway specimen exhibits superior interfacial bonding-tensile performances.