An experimental study of different factors affecting the bond of NSM FRP bars in concrete

Near-surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement has proven to be an efficient technique for strengthening concrete members. The bond behavior of the NSM system depends on the bond in the two existing interfaces, while the response in terms of load–slip curves and load capacity may be strongly affected by many other parameters. As a consequence of the variety of factors affecting the bond, different studies into the behavior of NSM FRP reinforcement have been carried out in recent years. In this paper, an experimental study is performed in which the effect of adhesive properties, bar type, bar size, FRP properties, groove geometry and the use of mechanical interlocking on the capacity and bond behavior of a NSM joint is investigated. The failure load, average bond stress, loaded end slip, free end slip, transverse strains (on adhesive and concrete), and the mode of failure for the tested joints are reported and discussed. The results show that the adhesive properties, FRP bar size and bar surface treatment were critical factors in the capacity and mode of failure of the specimens tested.