Post-heating flexural behavior of CFRP bar in ultra-high-performance fiber-reinforced concrete (UHPFRC) members after thermal exposure

The post-heating flexural performance of carbon fiber-reinforced polymer (CFRP) bars after thermal exposure plays a critical role in determining whether concrete members should be demolished or strengthened. This study investigates post-heating flexural performance of a CFRP bar in ultra-high-performance fiber-reinforced concrete (UHPFRC) after thermal exposure. A total of six UHPFRC members were prepared, and were exposed up to 200, 400, and 600 °C with unheated members serving as a control group, and the results were also compared to that of UHPFRC reinforced with steel bars. After thermal exposure at 200 °C, the ultimate load of the CFRP bar reinforced UHPFRC increased by approximately 16.7 % compared to the unheated member, but it dropped by 41.4 and 83.5 % after thermal exposure at 400 and 600 °C. For steel bar reinforced UHPFRC members, ultimate load decreased by approximately 33.4 %, with bar rupture observed after exposure at 600 °C. Thermal cracks appeared along the longitudinal direction after exposure at 400 °C, but no thermal cracks were observed after exposure at 600 °C. For CFRP bar reinforced UHPFRC members, the initiation of slip was accelerated with increasing temperatures, whereas almost zero slip was observed for steel bars at ambient and after thermal exposure at 600 °C. For sectional analysis, the materials were modeled to account for the modified tensile strength of CFRP bars after exposure at 400 and 600 °C. The flexural strength predicted by the sectional analyses showed good agreement with the experimental results, with an average ratio of 0.98 between experimental and predicted results.