Comparative fire behavior of geopolymer and epoxy resin bonded fiber sheet strengthened RC beams

This study presents results from fire resistance experiments on one RC control beam and seven fiber sheet strengthened RC beams, using geopolymer and epoxy resin as adhesive agents. Thermal response and deflection evolution of these beams with fire exposure time were monitored. The effectiveness of carbon fiber reinforced geopolymer (CFRG) strengthening system and carbon fiber reinforced polymer (CFRP) strengthening system at high temperatures is compared. Post-fire test observations and measured response parameters clearly show that the CFRG strengthening system remains fully effective at high temperatures, and thus CFRG strengthened beams experience lower deflections for longer duration (about 2 h) of fire exposure than corresponding CFRP strengthened beam with similar load levels. However, CFRG strengthened beams do not exhibit higher fire resistance than CFRP strengthened beam as anticipated. To explain this unexpected trend in results, detailed analysis, as well as numerous material level exploratory tests were conducted. The different failure mechanisms and additional contribution from cable action so as to enhance fire behavior of CFRP and CFRG strengthened beams were analyzed. Further test results and analysis clearly show that the early falling-off of fire insulation and fracturing of longitudinal CFRG system is the main cause for lower fire resistance in CFRG strengthened beams. When a layer of primer is applied between geopolymers and the insulation, the early falling-off of fire insulation can be prevented, and thus the fire resistance of CFRG strengthened beams can be enhanced (above 3 h).