Debonding Mitigation of Carbon Fiber-Reinforced Polymer- Strengthened Reinforced Concrete Beams with Grooved Bonding

This paper presents the potential and feasibility of an alternative bonding method for strengthening reinforced concrete beams with carbon fiber-reinforced polymer (CFRP) sheets. Periodic grooves are cut along the tensile soffit of the beams, in the transverse direction, on which CFRP is banded, and filled with an epoxy adhesive to lessen interfacial stresses. The tested bonding schemes comprise three grooves in the vicinity of CFRP termination (the CG3 series) and uniformly distributed grooves in the beam span (the CGD series). The behavior of these beams is investigated in comparison with that of unstrengthened and conventional CFRP-bonded beams with plain substrates. The grooved beams exhibit an over 46% higher load-carrying capacity relative to their conventional counterparts, dependent on a distance from the CFRP termination to the nearest groove. Despite the occurrence of CFRP delamination in the CG3 beams, the epoxy:filled grooves impede the propagation and thus improve the beams' failure loads. For the CGD beams, CFRP delamination is not observed until the beams fail by shear cracking and concrete crushing. The pre-yield stiffness of the grooved beams is enhanced due to the constrained concrete deformation and controlled cracking in tension. The CGD beams show a stable growth in CFRP strain compared with the CG3 beams that experience an irregular stress interaction between the CFRP and substrate. According to analytical modeling, the presence of the grooves at the CFRP termination decreases interfacial stresses by up to 78%. The energy release rate of the grooved interface is examined to account for the delamination mechanisms of the proposed bonding approach.