Experimental Study on the Bond Behavior of the CFRP Bar–UHPC Interface in Composite Anchorage

The bond performance at the interface between carbon-fiber-reinforced polymer (CFRP) bar and ultrahigh-performance concrete (UHPC) in composite anchorage was experimentally studied, and a suitable bar surface configuration was proposed. Pullout testing was performed on 36 specimens to evaluate the influence of surface treatment and anchorage length. Based on the results of the tensile testing, a formula for predicting the material properties of CFRP bar was proposed. Bar pullout is caused by the shearing off of the surface treatments, and the rupture is governed by the breaking load of the CFRP bar. The average bond strength improved with the increase in the depth–spacing ratio of rib, and decreased with the increase in anchorage length. The effect of the depth–spacing ratio on average bond strength was more remarkable in the specimens with a longer bonded length. The average bond strengths of smooth specimens were 13%–17% of that of the indented specimens. Additionally, the rib depth, groove width, rib spacing, and rib width were recommended as 0.03, 0.6, 1–1.2, and 0.4–0.6 times the bar diameter, respectively. Finally, formulas for calculating the average bond strength and critical anchorage length of the CFRP bar in the composite anchorage using UHPC as the bond medium were proposed.