Changes in fracture energy at FRP-concrete interfaces following indoor and outdoor exposure with sustained loading

Small-scale plain concrete precracked beams strengthened with carbon and glass fiber reinforced polymer (FRP) sheets were tested in 3-point flexure to evaluate changes in the FRP-concrete Mode II interfacial fracture energy following sustained loading for 6 and 13 years in indoor and outdoor environments. Mode II fracture energy of the interfacial region, G_F, was calculated using strain profiles along the length of the FRP sheet, which were measured using digital image correlation and photoelastic techniques. In the post-conditioned experiments, larger G_F values were measured as the debonded zone progressed from the sustained shear stress transfer region to the unstressed portion of the interfacial region far from the notch, particularly in beams with outdoor conditioning. In the interfacial region near the notch, the carbon FRP beams showed no reduction in G_F in the indoor environment but reduction in the outdoor environment, while glass FRP showed reductions in both environments. In outdoor beams with glass FRP sheets, G_F was not additionally degraded when the FRP was exposed to direct sunlight, in comparison to beams with the FRP exposed to indirect sunlight.