New hybrid cement-based composite material externally bonded to control RC beam cracking

This paper concerns the development of a new strengthening system for reinforced concrete beams that employs an externally bonded plate composed of composite fibre cement reinforced with fibre-reinforced polymer (FRP) rebars. The proposed approach involves preloading of a FRP rod and a precasting process. The paper deals with large-scale beams strengthened with an externally bonded carbon fibre-reinforced polymer (CFRP) plate or by using the near surface mounted (NSM) technique. These well-known techniques are compared with the proposed approach through four-point bending tests. The results are analysed with regard to the load–displacement curve, bending stiffness, cracking load, yield strength and failure load. It appears that the externally bonded reinforcement improves significantly the mechanical performance of the reinforced concrete beams both in service and at failure and compares favourably with the more usual techniques (CFRP, NSM) regardless the criterion retained. The bearing load is significantly increased (up to 63%). The bending stiffness of the strengthened specimen is improved due to an increase in inertia resulting from the strengthening plate. Also, except for the preloading beam, the kinematic of the crack width evolution is similar and the opening crack is significantly reduced in the same proportions than traditional solutions (CFRP, NSM). Finally, in order to integrate the crack opening as part of a design of the substitution proposed solution, an analytical model, although improved, is proposed and results are very encouraging.