Durability and Failure Modes of Concrete Beams Strengthened with Polyurethane or Epoxy CFRP

Externally bonded carbon-fiber-reinforced polymer (CFRP) composites are increasingly being used for repair of concrete infrastructure. Both the mechanical performance and the long-term durability of such a repair have resulted in a significant body of research. However, polyurethane-based composites for concrete repair have seen only limited treatment to date. This paper investigates the effect of seven different environments on the durability and failure modes of two different wet lay-up CFRP systems applied to flexural reinforcement of concrete: a two-part epoxy and a preimpregnated, water catalyzed polyurethane with aromatic chemistry as a matrix. Durability of concrete, CFRP laminates, and small-scale CFRP-strengthened concrete flexural beams was investigated for each duration (125, 250, and 365 days) and accelerated conditioning environment. Inverse analysis with a numerical model was used to develop conditioned bond–slip models for each composite system. Results and failure modes of control and conditioned specimens showed that degradation of CFRP-strengthened beams was controlled by the conditioned concrete tensile strength and bond cohesive energy in the epoxy and polyurethane systems, respectively.