Effect of fibers on the bonds between FRP reinforcing bars and high-strength concrete

This study evaluated the effects of synthetic and steel fibers on the bond properties of high-strength concrete and fiber-reinforced polymer (FRP) reinforcing bars. Direct bond tests were performed to evaluate the bond performance of 9-mm-∅ carbon fiber-reinforced polymer (CFRP) and 13-mm-∅ glass fiber-reinforced polymer (GFRP) reinforcing bars in three types of high-strength concrete with varying amounts of steel (20 and 40 kg/m3) or synthetic (4.55 and 9.1 kg/m3) fiber. The bond strength increased with the compressive strength of the high-strength concrete. The type and amount of fiber also affected the bond strength. The specimens with 40 kg/m3 steel fiber had the highest bond strength. The larger FRP bars tended to have stronger bonds, regardless of the strength of the concrete and type or amount of fiber. The relative bond strength was determined to analyze the effect of the type and amount of fiber; it increased as more fiber was added. Overall, the specimens with 40 kg/m3 steel fiber had the best bond performance.