Interface Shear Capacity of Rough and Smooth Concrete Interfaces with GFRP Shear-Friction Reinforcement

Glass fiber‒reinforced polymer (GFRP) has emerged as a promising alternative to steel reinforcement, owing to its light weight and corrosion resistance. Despite its advantages, research on GFRP as shear-friction reinforcement remains limited. This study investigated the behavior of rough and smooth concrete cold joint interfaces reinforced with GFRP shear-friction reinforcement. Fourteen push-off specimens were tested under monotonic loading, with key parameters including the interface condition (rough/smooth), reinforcement ratio (0.26%–1.57%), and reinforcement material (steel, GFRP). The findings demonstrated that GFRP reinforcement significantly enhanced the load-carrying capacity and reduced the likelihood of sudden failure, as observed in unreinforced specimens. In roughened cold joint interfaces, GFRP reinforcement ratios of 0.53%, 1.05%, and 1.53% led to shear capacity increases of 11%, 80%, and 97%, respectively, compared with unreinforced specimens. For smooth cold joint interfaces, GFRP reinforcement enhanced the shear stress at failure up to 4.7 MPa, compared with the negligible resistance of unreinforced specimens. Roughening the interface notably enhanced the load-carrying capacity of the specimens. For smooth cold joint interfaces, dowel action primarily governed the shear transfer, with GFRP-RC specimens performing comparably to the steel‒RC specimen. However, the steel‒RC specimen outperformed the GFRP-RC specimens with rough interfaces. The Canadian Standards Association Group’s highway bridge design code provided conservative predictions for GFRP-RC specimens, whereas AASHTO’s equation for GFRP-RC overestimated the interface shear capacity. A modified equation for predicting the interface shear capacity of GFRP-RC cold joints was proposed in this study, offering more accurate yet conservative predictions based on both experimental results and literature data.