Experimental and theoretical studies on bond behavior between concrete and FRP bars with different surface conditions

Design of bond length of over-crowded rebar becomes a remarkable challenge in the critical loaded structure members. Enhancing bond strength between concrete and rebar is a feasible way to improve this situation, which can be realized by improving the bar surface condition (i.e., rib height and rib space). However, effect of these two parameters on the bond performance are not comprehensively studied. In this paper, 16 groups including 48 samples were tested, in which three types of bars (i.e., steel bar, glass fiber-reinforced polymer (GFRP) bars and basalt fiber-reinforced polymer (BFRP) bars) with different surface conditions were considered. To study the adhesion and friction effect, Scanning-Electron-Microscope (SEM) observations were performed. When the rib effect on the bond performance was investigated, the bond strength caused by adhesion and friction effect was excluded from the bond strength of ribbed bars. Experimental results indicate that bond strength can be enhanced if bars with larger rib height is used. To predict the bond strength that can consider the effect of rib height, a theoretical model is developed.