Bond Behavior between Reinforcing Steel and Recycled Coarse Aggregate Concrete after Carbonation

There is a noticeable research gap concerning the durability of recycled concrete, a pivotal resource for fostering urban sustainable development. This paper presents the results of an investigation into the bonding characteristics between complete carbonation recycled aggregate concrete (RAC) and reinforcing steel. Test specimens were meticulously prepared, incorporating five distinct replacement ratios (0%, 30%, 50%, 70%, and 100%) of recycled coarse aggregate (RCA). These specimens were subsequently categorized into two groups: one featuring stirrup reinforcement and the other devoid of it. Following accelerated carbonation, pull-out tests were diligently conducted. The outcomes of these tests revealed that specimens with stirrup reinforcement exhibited pull-out failure, whereas those without stirrup reinforcement underwent splitting failure. As the replacement ratio of RCA increased in complete carbonation pull-out specimens, there was an observed decrease in bond strength, slip value, and steel strain. Relative to natural concrete (NC), RAC70 exhibited a decrease in ultimate bond strength of 1.46 MPa, whereas RAC100 showed a decrease of 1.63 MPa. Additionally, the bond-slip curve displayed a diminished slope with higher replacement ratios. Furthermore, the peak value of the bond stress distribution curve shifted toward the free end with an increasing RCA replacement ratio. Complete carbonation recycled concrete exhibited heightened compressive strength, improved bond strength, and a steeper ascending segment in the bond-slip curve. The ultimate bond strength of NC-confined specimens increased by 26.76%. Conversely, for specimens with 70% and 100% replacement rates, the ultimate bond strength only increased by 9.55% and 3.89%, respectively. Furthermore, a constitutive relationship model for the bond slip between complete carbonation recycled concrete and reinforcing steel was formulated based on the empirical findings. Ultimately, the bond stress distribution curve reveals two peak points, observed near the loading end and the free end, respectively, with a more pronounced gap between the two peaks after complete carbonation. As the replacement rate of recycled aggregates increased, the maximum bond stress tended to shift toward the free end. When the replacement rate reached 100%, the gap between the two peak points significantly diminished.