Behaviour of NSM FRP masonry bond under elevated temperatures

Fibre-reinforced polymers (FRPs) have become increasingly popular as reinforcement to strengthen unreinforced masonry (URM) walls due to their high strength/stiffness to weight ratios, corrosion resistance and low on site handling costs. However, the strengthening systems suffer potential limitations 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 tests, used to characterise the behaviour of the FRP to masonry bond, was conducted. Some tests were conducted at elevated temperatures to determine the surface temperature at which the reinforcing becomes ineffective. Further tests were conducted after first heating beyond the glass transition temperature for the epoxy adhesive and then cooling the specimens to determine whether the damaging effect of elevated temperatures is reversible. The study considered one arrangement of near surface mounted 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 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 reported glass transition temperature. For specimens which were heated to temperatures of 150°C and 200°C and then cooled prior to loading, the original bond strength was restored and the failure mode and displacement capacity also matched that of the control specimens