Deterioration of FRP/concrete bond system under variable moisture conditions quantified by fracture mechanics

Fiber reinforced polymer (FRP) retrofit systems for concrete structures have been widely used, and studies on their short-term debonding behavior have been extensively conducted. Nevertheless, long-term performance and durability issues regarding debonding behavior in such strengthening systems still remain largely uncertain and unanswered. Due to its composite nature, the effectiveness of the strengthening system largely depends on the properties of the interface between the three constituent materials, namely concrete, epoxy, and FRP. Many factors can cause degradation of the interface properties, especially environmental exposure during service life. In this study, effects of moisture on concrete/epoxy/FRP bond system is characterized by means of the tri-layer fracture toughness, which can be obtained experimentally from peel and shear fracture tests. An irreversible weakening in bond strength has been observed in fracture specimens under moisture cyclic condition. Based on the experimental results of fracture specimens under variable moisture conditions, an empirical model can be developed to predict service life of FRP-strengthening system.