Influence of recycled coarse aggregate content on bond strength and invalidation mechanism between steel tube and recycled aggregate concrete

In order to explore the influence of recycled coarse aggregate (RCA) replacement ration on the bond strength and failure mechanism of steel tube and recycled aggregate concrete interface, 15 recycled aggregate concrete-filled circular steel-tube short columns and 9 recycled aggregate concrete-filled square steel-tube short columns were designed for the push-out test. Two parameters of concrete strength grade and length-diameter ratio were grouped so as to analyze the effect of RCA replacement ration. Based on the test, the characteristic point parameters in load-slip curves were obtained and ultimate bond strength calculation formulas were fitted. The influence of RCA replacement rate on the invalidation mechanism was researched in interface energy consumption, bonding shear stiffness and damage. The results show that there is a good agreement between formula calculated values and test measured values. There is no efficient effect of RCA replacement ration changing on the interface energy dissipation during the process of bond failure. The interface elastic bond shear stiffness decreases with the increasing of RCA replace ration, and the rate of stiffness degradation behaves different. Due to the adhesive cement matrix and internal cracks of RCA, they will accelerate the bond damage process on the interfacial between steel tube and RAC.