Flexural Strengthening of Reinforced Concrete Beams Using Externally Bonded Polyurethane Carbon Fiber-Reinforced Polymer Composite Systems

Externally bolded carbon fiber-reinforced polymer (CFRP) composites air an effective method for flexural and shear strengthening and repair of reinforced concrete (RC) beams. In externally bonded CFRP strengthening, epoxy-based CFRP wet layup systems are predominately used. CFRP composites pre-impregnated with polyurethane (PU) resin and PU primers were demonstrated as an effective alternative in previous studies yet have seen limited applications. Due to the broad range of PU primer and laminate properties, bond between PU-CFRP system and concrete substrate can be potentially promoted. This paper experimentally characterizes the performance of six different PU-CFRP systems for external flexural strengthening of RC beams and investigates the relationship between bond-slip properties and the target flexural responses. Twenty-one lap shear specimens, 30 concrete flexural beams, and seven RC flexural girders were tested and compared with a conventional epoxy-based wet layup system and non-CFRP control specimens. Results indicated that PU adhesive and laminate can be tailored to obtain desired flexural performance, with bond cohesive enemy and shear slip being the parameters that best predict the flexural beam strength, deformability, and failure modes. Comparable flexural capacity improvement was also observed between the PU-CFRP and the epoxy-based CFRP wet layup systems.