Analyzing bond characteristics between composites and quasi-brittle substrates in the repair of bridges and other concrete structures

During the last two decades, externally bonded fiber-reinforced polymer (FRP) composites have been widely used for strengthening, repairing, and rehabilitating reinforced concrete (RC) structural members. The bond characteristics contribute to the effectiveness of the stress transfer achieved between the FRP composite and the concrete substrate. Debonding of the FRP composite reinforcement is the most critical concern in this type of application. Under monotonic and fatigue-loading conditions, FRP-concrete shear debonding has been idealized as a Mode-II fracture problem along the bi-material interface. A cohesive material law is used to describe the interfacial stress transfer at the macroscopic level. The area under the entire curve represents the fracture energy, and is related to the load-carrying capacity of the interface. In this chapter, previous experimental results published by the author are discussed to show how the fracture energy can be considered a true fracture parameter. The results are instrumental in discussing the strain limits provided in international codes and guidelines. Future research needed and newly developed composites are introduced at the end of the chapter.