Mechanics of Bond Fatigue Behavior of Concrete Beams Strengthened with NSM CFRP Rods

Abstract

Bond tests were conducted on 28 concrete beams strengthened with near-surface mounted (NSM) carbon-fiber-reinforced polymer (CFRP) rods under different fatigue load levels. In the NSM technique, the CFRP rods are placed inside precut grooves and bonded to the concrete with epoxy adhesive. The test variables included: presence of internal tension steel reinforcement (unreinforced or reinforced), type of CFRP rod (spirally wound or sandblasted), and the fatigue load level. The beams were tested in four-point bending. Bond failure was by debonding between the CFRP rod and the epoxy that started at sections close to the beam midspan. As the load was cycled further, debonding propagated toward the supports. At failure, the beams strengthened with a given rod type (sandblasted or spirally wound) showed the same CFRP strain at sections close to the support. The sandblasted rods showed a better bond fatigue performance than the spirally wound rods, which, at a given load level, failed at a higher number of cycles.