Review of near-surface mounted FRP plates in the strengthening of continuous flexural members and bond behaviour

Bonding carbon fibre-reinforced polymers (FRP) to reinforced concrete (RC) flexural members has become a popular means to enhance load carrying capacity and prolong service life. Considering the type of FRP strengthening system, the near-surface mounting (NSM) technique of embedding FRP strips in saw-cut grooves within the concrete cover of RC members to flexurally strengthen beams and slabs is known to have desirable bond behaviour benefits over external bonded FRP plates. Further the NSM technique has attracted growing attention in strengthening of statically indeterminate RC members. However, little is known about the durability of the critical bond between the embedded FRP and the concrete when installed using this technique. In this paper, experimental results of continuous flexural members strengthened with NSM FRP is collated and reviewed to investigate failure modes, ductility and moment redistribution capability. Ductility and moment redistribution characteristics of strengthened RC members relies on the bond performance of reinforcement to concrete and hence this paper also reviews durability testing of NSM joints. Regression analysis shows that concrete compressive strength and steel reinforcement ratios are paramount to maintaining ductility under all strengthening schemes.