NSM CFRP composites for effective tension zone of reinforced concrete members subjected to wet-dry cycling

Abstract

This article presents an experimental study concerning near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) composites for the effective tension zone of a reinforced concrete beam. The test specimen consists of a concrete prism with one No. 3 reinforcing steel bar, representing the effective tension zone, and is preloaded to 50% of the cracking load of the specimens to simulate existing concrete structures in service conditions. A total of 16 specimens, 11 of which are retrofitted with NSM CFRP strips, are monotonically loaded in axial tension until failure takes place. Of particular interest is the interaction between the concrete and the reinforcement at service load levels when exposed to wet—dry environment. Test parameters include the effect of wet—dry cycles, the type of bonding agents (epoxy adhesive and cement-grout), the number of CFRP strips, and the size of groove for the composite. The specimens with epoxy adhesive show better performance than those with cement-grout, while the contribution of the geometrical properties (e.g., groove size and number of CFRP strips) to the behavior of the retrofitted specimens is not significant. The variation of a tension stiffening index and the effective axial stiffness is studied to examine the effects of wet—dry cycles on the serviceability of the retrofitted specimens.