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.

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