Experimental study on the bond behaviour of the concrete-CFRP interface

FRP materials have been widely used to either strengthen or rehabilitate many concrete structures in numerous applications. Since epoxy is usually used for bonding, the tensile stresses are being transferred from the FRP to concrete by means of the bonding interface. Effort is still being made to fully understand the conditions at the concrete-FRP interface in order to improve the design of concrete structures externally strengthened with FRP. Various studies have been pursued to define and correlate the parameters that can influence the bond behaviour. Another significant issue is that high shear stress concentrations are generated at the end of the externally bonded reinforcement where the forces have to be transferred between FRP and concrete. Therefore, it is of great importance to determine the effective bond length of FRP materials. Researchers have come up with a many estimations for the effective bond length needed to achieve the bond strength capacity. A reliable value must be achieved in order to have a safe design. The present research was to study the effect of the parameters that are believed to influence the behaviour of the concrete-CFRP interface the most. The effective length required to achieve the bond strength capacity was also determined. The behaviour of thirty two specimens and two control specimens has been reported in details. This study concludes that the maximum load carrying capacity and bond strength increases when cross wraps are located on both halves of the specimen, the specimen has rough surface, or the bond length increases. However, the maximum load carrying capacity increases but bond strength decreases when the bond width increases or CFRP stiffness increases. Finally, the effective length obtained was less than 100 mm in most cases