Bond Performance of Near-Surface-Mounted FRP Bars

Near-surface-mounted (NSM) reinforcement has become a well-known method for strengthening existing concrete structures. The bond between the NSM reinforcing bars and concrete is the key factor in the NSM technique. In the NSM technique, there are two bond interfaces: one between the NSM bar and the adhesive, and the other between the adhesive and the concrete. For this technique to perform efficiently, these two interfaces need to be investigated. On the other hand, concrete structures that require rehabilitation are often exposed to aggressive environments. Many of these environments are related to cold-climate conditions as can be found in Canada. Environmental factors including freeze/thaw action, exposure to deicing salts, and sustained low temperatures combine to attack the integrity of repaired structures. Consequently, repair materials for the Canadian infrastructure must be able to withstand these harsh conditions for prolonged periods of time. A total of 80 NSM-fiber-reinforced polymer (FRP) bars installed in C-shaped concrete specimens were tested in pull-out setup to failure. Sixty specimens were tested at normal room temperature, while the remaining 20 specimens were tested after conditioning in an environmentally controlled chamber for 200 freeze/thaw cycles. The dimensions of the specimens were designed, upon a preliminary phase of testing, to ensure that no transverse cracking would occur in the specimen before bond failure of the NSM bar. The results are presented in term of failure load, average bond stress, strains in FRP bar, end slip, and mode of failure. A bond-slip model was proposed for the used FRP bars.