Bond Behavior Between Recycled Concrete and Corroded Ultrahigh-Strength Steel Bars

Forty-five pull-out tests were carried out to investigate the bond behavior between recycled aggregate concrete (RAC) and ultrahigh-strength steel bars (UHSSBs) with spiral grooves. Bond performance influencing factors were taken into account to analyze the ultimate bond stress and slip, bond energy absorption, bond stiffness and residual bond stress, including UHSSB corrosion levels from 0 to 11%, recycled coarse aggregate (RCA) replacement ratios from 0 to 100%, stirrup ratios from 0.51 to 1.03%, UHSSB embedded length from 10d to 20d, concrete cover thickness from 30 to 70 mm, and anti-rust coating. Pull-out failure was observed in all specimens, and the experimental results showed that the bond strength and bond stiffness initially increased when the corrosion level was no more than 1.5% and then decreased with increasing corrosion levels. Corrosion-induced bond degradation decreased with increasing stirrup ratios and concrete cover thickness, and bond strength decreased with increasing embedded length of UHSSB and RCA replacement ratios. The anti-rust coating can effectively prevent UHSSBs from rusting but can lead to a decrease in bond strength by 37.3%. A bond strength model was proposed considering the corrosion levels of UHSSBs and RCA replacement ratios with presented predictions for the bond stress-slip relationship, which provided a reference for engineering design.