Bond characteristics of near surface mounted CFRP bars

Near Surface Mounted (NSM) strengthening is an emerging retrofit technique, which involves bonding fibre reinforced polymer (FRP) reinforcement into grooves cut into the surface of a concrete member to be strengthened. This technique offers many advantages over external bonding of FRP reinforcement, for example, an increased bond capacity and protection from external damage. To date, significant research has been conducted into the NSM FRP strengthening technique. However, there are still some areas which need further research in order to fully characterise bond and anchorage of these bars. The particular objectives of this research were: to investigate bond behaviour of NSM FRP bars, to understand the critical failure modes involved, and to predict bond strength and anchorage length requirements. Several significant variables affecting bond, such as bond length, bar shape and groove dimensions have been considered, and the results are presented and discussed in this paper. It is seen that for both circular and square bars with relatively high cross-sectional area/perimeter ratios, concrete cover separation failure is the upper-bound failure mode which limits the load capacity when the other influencing parameters, such as bond length, resin cover thickness and concrete strength, are optimised. For rectangular bars, tensile rupture of the FRP is seen to be a limiting condition.