Effect of different material and construction details on the bond behaviour of NSM FRP bars in concrete

The use of FRP bars and strips as near-surface mounted (NSM) reinforcement has become an emerging technique for the strengthening of reinforced concrete (RC) members. The bond between NSM FRP reinforcements and concrete is a crucial factor affecting the efficiency of this technique. Many factors involving the interaction between FRP reinforcement, adhesive and concrete can affect the bond behaviour and failure load of the NSM strengthening system. In this paper, the modified pullout test (adapted to NSM reinforcement) is used to study the effect of groove surface (pre-formed and saw cut), groove geometry (dimensions and shapes), FRP bar type (material and surface treatment), bond length; and also of the incorporation, in the groove–concrete system, of different construction details that modify the NSM–concrete interaction (transverse interlocking with or without shear connectors, covering plate with shear connectors and confinement of surrounding concrete). The tested specimens had different bond behaviours and modes of failure: bar–epoxy interface failure, epoxy failure with concrete splitting, concrete–epoxy interface failure and tensile failure of the concrete specimen. The effects of the introduced variables on the response of the specimens are presented and discussed.