Circular RC columns wrapped with PBO-FRCM and CFRP strengthening systems in a standard fire

The fire performance of reinforced concrete (RC) columns strengthened with fiber-reinforced polymer (FRP) or fabric-reinforced cementitious matrix (FRCM) systems remains a concern. For an FRP strengthening system to be considered effective during a fire, its fire performance must be defined using adequate fire protection. Without proper fire protection, FRP loses effectiveness early in a fire event. Four circular columns (800 mm in length) were exposed to ASTM E119 standard fire for 180 min with a sustained load equal to 13 % of their capacity. Carbon FRP wraps and FRCM with poly benzo isoxazole (PBO) grids were used for strengthening the columns. Two types of fire protection systems examined including spray applied fire-resistant material (SFRM) and intumescent paint (IP) coatings. Results showed significantly lower temperatures in columns wrapped with FRCM compared to the one wrapped with CFRP sheets. The SFRM-insulated column demonstrated superior performance, maintaining concrete core temperatures below 130 °C throughout the entire fire exposure period. A key observation was the quick ignition of the CFRP beneath the IP coating, which caused a rapid temperature increase, localized concrete spalling due to the mismatch in thermal expansion between the CFRP sheets and concrete, and early exposure of the steel reinforcement. It is recommended to apply the IP coating carefully over combustible materials like FRP, as its fire protection capability may diminish within the first 30 min of the fire test. While SFRM performed well, combining FRCM with SFRM offers a more effective approach to enhancing the fire resistance of RC columns.