Deterioration of the FRP-to-concrete interface subject to moisture ingress: Effects of conditioning methods and silane treatment

Fiber reinforced plastics (FRP) composites have emerged as one popular material in retrofitting/rehabilitation of concrete structural members in last decades. The long-term durability of the FRP-to-concrete interface in aggressive environments plays a critical role in the success of this technique. An experimental program has been carried out in this study to examine the effect of moisture on the deterioration of the FRP-to-concrete interface. In addition to conditioning the specimens through fully submerging the specimens in water, a new method to condition the specimen through submerging only the bottom half of the specimen in water was used in this study. Testing results suggest that the fracture toughness of the FRP-to-concrete interface conditioned through half immersion is significantly higher than that of the interface conditioned through full immersion. Three possible responsible mechanisms have been identified: different moisture distributions along the epoxy-concrete interface induced by conditioning methods, faster moisture diffusion through the epoxy-concrete interface, and hygroscopic swelling stress induced by the swelling of the epoxy after absorbing moisture. The significant effect of the conditioning method on the durability of the FRP-to-concrete interface makes us postulate that the laboratory testing based on full immersion of the specimen in water could exaggerate the deterioration of the interface induced by the moisture in real applications, in which the interface is exposed to air, rather than water. In such a case, neither the moisture diffusion along the epoxy-concrete interface nor the swelling of the interface is as significant as in the case of full immersion in water used in the laboratory testing. In addition, this study also evaluated the potential of silane coupling agent on enhancing the durability of the FRP-to-concrete interface in moisture conditions.