Behaviour under elevated temperatures of the bond between near surface mounted fibre reinforced polymer reinforcement and clay brick masonry

Over the past two decades researchers have investigated the use of fibre reinforced polymers (FRPs) as reinforcement to strengthen deteriorated or understrength unreinforced masonry (URM) walls. FRPs are attractive due to their high strength/stiffness to weight ratios, corrosion resistance and low on site handling costs. However, there are limitations regarding the durability of the systems particularly when subjected to elevated temperatures because the epoxy resins used to bond the FRP to the masonry lose strength and stiffness at relatively low temperatures. To explore this effect, a series of pull off tests, used to characterise the behaviour of the bond between the FRP reinforcement and the masonry substrate, were conducted. Some tests were conducted at elevated temperatures, and some after first heating beyond the glass transition temperature for the epoxy adhesive and then cooling the specimens. The former were used to determine the surface temperature at which the reinforcing becomes ineffective and the latter to determine whether the damaging effect of elevated temperatures is reversible. The study considered one arrangement of near surface mounted (NSM) carbon FRP strip reinforcement and epoxy adhesive. It was found that under sustained load, relative movement between the reinforcement and masonry initiated at temperatures close to the manufacturer’s reported glass transition temperature for the epoxy adhesive used. However, loss of strength and subsequent complete debonding did not occur until the surface temperature reached 140°C (mean value), some 80°C higher than the manufacturer’s reported glass transition temperature for the epoxy adhesive tested. For specimens which were heated and then cooled prior to loading, the original bond strength was restored but the ductility of the bond-slip relationship was reduced compared to control specimens