While research on debonding of FRP (fiber reinforced polymer) retrofitted concrete systems have been conducted extensively for short-term mechanical characterization, long-term performance and durability issues regarding such debonding behavior remain largely uncertain and unanswered. In particular, little is known with regard to the effect of moisture on bond properties and integrity of FRP retrofitted concrete that would govern the effectiveness and life cycle of these systems. The objective of this research is to develop an in-depth mechanistic understanding of moisture affected debonding in CFRP (carbon fiber reinforced polymer) plated concrete using an interface fracture approach, which rigorously quantifies the debonding problem by means of interface fracture toughness of the bonded system. While the strength approach is capable of quantifying and analyzing material decohesion type of debonding, it intrinsically lacks the ability to describe adhesion related phenomena. Interface fracture toughness is, on the other hand, considered a bond property of the multi-layer material system, and is a quantification parameter central to this proposed research. We propose to conduct the investigation by means of a synergistic effort that consists of systematic and hierarchical material and interface fracture testing and analytical investigation. Analytical modeling of debonding under moisture cyclic and viscoelastic effects, numerical studies that consist of three-dimensional moisture diffusion simulation, interface fracture analysis that consists of kink criterion implementation and mode-mix characterization will be performed, as well as correlation studies to draw links between local fracture energy and external load configurations at the beam scale. The toughness parameter, which will be used throughout the study, will be computed from a model recently developed from prior NSF-funded research by the research group of the PI, that is capable of describing the tri-layer material problem consisting of FRP, epoxy, and concrete. It is expected that the fundamental knowledge to be developed from this research will form the basis for augmenting existing design specifications for FRP retrofitted concrete structures by accounting for moisture effects in such systems.
