Bond behavior between recycled aggregate concrete and deformed rebar after Freeze-thaw damage

In this study, the internal cracks and residual deformation, as well as the damage mechanism of both natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) after different freeze-thaw cycles (0, 50, 100, 150, 200, 250, and 300) were firstly investigated. After that, 51 axial pull-out tests were carried out to analyze the influence of two comprehensive orthogonal parameters, the replacement percentage of recycled coarse aggregate (0, 50%, and 100%) and the number of freeze-thaw cycles (0, 50, 100, 150, 200, 250, and 300) on the peak bond strength and peak slip between RAC and deformed rebar. A bond strength degradation model with splitting tensile strength as the damage factor was established. The "softened inner layer + elastic outer cylinder" theory was modified, and the theoretical calculation equations of peak bond strength and yield bond strength between deformed rebar and RAC after freeze-thaw damage were also proposed. The results showed that as the number of freeze-thaw cycles increased, the bond behavior between RAC and deformed rebar gradually degenerated, the peak bond strength decreased gradually, while the peak slip decreased first and subsequently increased. The replacement percentage of recycled coarse aggregate affected the bond behavior differently for different freeze-thaw cycles. When the number of freeze-thaw cycles was small, the bond strength between RAC and deformed rebar was poorer than that between NAC with the same compressive strength and deformed rebar. However, with the increase of the number of freeze-thaw cycles, the bond strength between RAC and deformed rebar was superior to that between NAC and deformed rebar. The fitting and theoretical equations of bond strength proposed in this study were in good agreement with the experimental results. (C) 2020 Elsevier Ltd. All rights reserved.