Stress Transfer between FRP Laminates and Concrete through Deteriorated Concrete Surfaces

This study investigated the mechanism of stress transfer between glass and carbon fiber-reinforced polymer (FRP) laminates and concrete beams with deteriorated surfaces. Thirty-six beams were prepared with either a solid concrete cross section, or with a weak concrete layer at the surface, simulating the state of a deteriorated surface. The beams were reinforced with glass or carbon FRP sheets and tested in flexure. Strain development in the laminate and in the concrete layers was recorded and analyzed. The mode of failure changed from shear within the deteriorated layer of concrete to delamination at the interface between the resin and the concrete in the solid high-strength concrete. A significant amount of stress was transferred between the FRP laminates and the concrete surface probably by residual frictional stresses after shear cracks developed in the deteriorated layer, leading to a remarkable load bearing capacity of these beams.