Effects of elevated temperature on near surface mounted and externally bonded FRP strengthening systems for concrete

Near surface mounted (NSM) fibre reinforced polymer (FRP) reinforcement is an effective technology for strengthening concrete structures in both flexure and shear, and has numerous advantages over externally bonded FRP. Available research on NSM systems for concrete has focused predominantly on overall member behaviour and/or parameters affecting NSM bond performance; relatively little research has been performed to study the response of NSM systems at elevated temperatures, as would be experienced during a fire. All FRP strengthening systems are susceptible to deterioration of mechanical and bond properties at elevated temperatures due to the comparatively high sensitivity of polymer adhesives and matrices to temperatures in the range of their glass transition temperature (Tg). It has been suggested in the literature that, thanks to superior bond performance and thermal protection from embedment within the concrete cover, NSM systems may outperform externally bonded FRP systems at elevated temperatures, particularly if inorganic adhesives are used; little research is available to support these claims. Experiments were performed to investigate and compare the performance of NSM and externally bonded FRP flexurally strengthened concrete beams under sustained load at temperatures exceeding the matrix/adhesive polymers’ Tg. Results suggest that both NSM and externally bonded FRP strengthening systems are susceptible to elevated temperature, but that their performance can be considerably better than is commonly believed.