Research on chloride ion permeability resistance of concretes bonded with CFRP sheets under dry-wet cycles

Considering the widespread application of carbon fibre-reinforced polymer (CFRP) as a protective material for reinforced concrete (RC) structures, this study focuses on the ability of CFRP laminates with different numbers of layers bonded to the concrete surface to reduce the ingress of chloride ions. Variations in the free chloride concentration distribution in concrete before and after CFRP bonding were explored systematically. Nonlinear fitting was applied to the experimental data to establish a calculation model for the diffusion of free chloride ions in concrete with CFRP bonded to the surface, which was subsequently validated. Based on the proposed model, the reduction in the surface chloride concentration of concrete after bonding different numbers of CFRP layers was quantified as the reduction value. Moreover, recommendations for the durable design of RC structures bonded with CFRP in wet-dry cyclic environments are provided. The results indicate that the surface chloride concentration in concrete increases continuously with increasing wet-dry cycles, eventually reaching a steady state. Compared with the concrete specimens without CFRP bonding, the bonding of one, two, or three layers of CFRP led to reductions in the stable surface chloride concentration of concrete by 70.8%, 82.6%, and 84.9%, respectively. And no obvious convection zone was observed in the concrete after CFRP bonding. The validation results of the proposed calculation model demonstrated its high accuracy, making it suitable for durable design and service life prediction.