Insight into the Mechanical Performance of the UHPC Repaired Cementitious Composite System after Exposure to High Temperatures

In this paper, the mechanical performance of an ultra-high-performance concrete (UHPC) repaired cementitious composite system, including old matrix and new reinforcement (UHPC), under various high temperature levels (20 °C, 100 300 500 °C) was studied. UHPC reinforced with different contents steel fibers polypropylene (PP) utilized. Moreover, physical, compressive, bonding, flexural behaviors system after being exposed to temperatures were investigated. Meanwhile, X-ray diffraction (XRD), baseline evaluation test (BET), scanning electron microscope (SEM) tests conducted analyze effect on microstructural changes in a system. Results indicate that appearance bonded changed, its mass decreased slightly. The average percentage residual 99.5%, 96%, 94–95% at respectively. compressive strength, bonding improved first then deteriorated increase temperature. When reached strength by about 20%, 30%, 15% for Under temperature, original components pore structure deteriorated. cumulative volume °C could reach more than three times room (about 20 °C). showed obvious deterioration, interfacial became looser exposure