Thermo-mechanical Bonding Behaviour of CFRP NSM System Using Cement-Based Adhesive

Abstract

Near surface mounted (NSM) strengthening technique, using fiber reinforced polymer (FRP) composite materials, is one of the most promising solutions for dealing with the deterioration problems of current reinforced concrete (RC) structures. However, intense research is still ongoing to keep improving this technique in the cases where its application shows limitations, e.g. in cases of fire hazard. The bonding in NSM systems is usually guaranteed by polymeric matrices like epoxy adhesives. However certain drawbacks result from the use of these adhesives, such as low resistance to elevated temperatures. This characteristic leads to premature failure under these circumstances, preventing the mobilization of the exceptional load carrying capacity of carbon fibers. Thus, the development of solutions involving alternative adhesives seems technically and economically relevant. Cement-based materials, which are incombustible and show low thermal diffusivity, show great potential as a valid alternative. Recent investigations suggest the possibility of transferring stresses between the NSM system and concrete substrate using cementitious matrices. However, the performance of these materials in different loading conditions, including high temperature exposure, need to be better explored. This paper presents a study on the characterization of the bonding performance of CFRP NSM strengthening technique with cement-based adhesives using innovative surface treated carbon laminates installed into deep grooves. The CFRP laminates used in this study were manufactured specifically with sand-treated surfaces to improve the bonding performance between CFRP and cement-based adhesive by taking advantage of the better grip of the increased roughness surfaces. The results of the pull-out tests in ambient conditions, as well as after the exposure to elevated temperatures, are discussed. Monotonic bond tests results confirmed the effectiveness of the proposed approach for enhancing the bond strength in NSM CFRP system. Thermo-mechanical tests showed that the governing failure mode in the adopted system was slipping the CFRP reinforcements from adhesive medium.