Experimental and theoretical issues in FRP-concrete bonding

Delamination phenomena between fiber reinforced polymer (FRP) strips and concrete support are investigated on the basis of single lap shear tests. To capture a stable post-peak response of the FRP-concrete joint, the slip between the concrete support and the reinforcement strip using a clip gauge mounted at the end of the reinforcement was the control signal during the tests. This allowed stable fracture propagation in the descending branch until complete load relaxation and debonding. In addition, a formation of a concrete bulb at the end of the reinforcement was observed, and the concrete bulb has a not negligible influence on the maximum load transmitted by the joint. The problem of predicting the ultimate interfacial load and the corresponding bond length is generalized considering reinforcements having a non-linear constitutive behavior, and expressions for both ultimate interfacial load and the corresponding anchorage length are proposed. The model was applied to an external reinforcement bonded to a concrete substrate. In this case, it is shown that a minimum value for the anchorage length must be identified as a solution of a variational problem. In the case of external reinforcement with a bonded length equal to the minimum value, the bond resistance at failure is comparable with bond strengths of longer adhesive joints.