Monotonic and cyclic loading tests of reinforced concrete beam strengthened with bond-improved carbon fiber reinforced polymer (CFRP) rods of ultra-high modulus

Abstract

Abstract The present study focuses on a near-surface-mounted (NSM) strengthening technique for cantilevered-reinforced concrete (RC) bridge-deck slabs subjected to wheel loads. A carbon-fiber-reinforced polymer (CFRP) rod of ultra-high modulus (455 GPa) is used in the NSM technique adopted in this study. In particular, the fatigue durability of the RC member strengthened with the NSM CFRP rods was examined. Notably, the ultra-high modulus CFRP rod has no shear-resistant ribs because of the pultrusion manufacturing process. Hence, the greatest concern in the strengthening of the NSM is the significant low-bonding property of the CFRP rod embedded in covering/filling materials, such as concrete, mortar, and epoxy-resin. The study uses the CFRP-rod attaching glass-fiber-reinforced polymer (GFRP) ribs to improve bond strength. The bond-improved CFRP rod, with a small diameter of 8–14 mm, can be embedded in the high-strength mortar replacing the upper-cover thickness of general RC slabs. In this study, 15 RC beam specimens of 160 mm thickness were prepared, which is the minimum thickness of a Japanese highway slab. Thirteen beams strengthened with NSM-CFRP rods were tested by monotonic and cyclic loadings, respectively. The flexural fatigue test confirmed that the strengthened beams endured 2 million cycle loadings, and the CFRP rods were firmly bonded in concrete, even under a repeated load. The study reveals the excellent load-carrying capacity and fatigue durability of the RC member, strengthened by NSM-CFRP rods of ultra-high modulus.