Bond Strength between Recycled Concrete and Rebar under Stirrup Constraint after Freeze-thaw Cycles

In cold regions, freeze-thaw (F-T) damage is the main detriment to the durability of reinforced concrete structures, which will reduce the bond performance between concrete and rebar, and then adversely affect the bearing capacity and stiffness of structures. In this study, 21 groups of tests were performed to analyze the effects of the number of F-T cycles, volume stirrup ratio, and replacement percentage of recycled aggregate on the bond performance between recycled aggregate concrete and deformed rebar. The stirrup stress during the pulling process was measured using strain gauges attached to the stirrup surface, and the contribution of the stirrup to the bond strength was analyzed. The results showed that the F-T damage and stirrup constraints could affect the failure mode, the bond strength and the peak slip of pullout specimen. The failure mode of specimen with stirrups could be determined by splitting angle index. The indirect contribution of stirrup accounts for 14-25% of the bond strength and increases with the increase in F-T damage. The full bond-slip curve was obtained by fitting four parameters including splitting tensile strength, constraint coefficient, splitting angle index and brittleness index.