Bond behaviour of RACFST stub columns after exposure to high temperatures

The bond behaviors of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposure to high temperatures were investigated based on the push-out experimental tests of 36 heated and six unheated RACFST specimens. The influences of five variable parameters, that is, temperature level, replacement ratio of recycled coarse aggregate (RCA), cross-section type, concrete strength and interface length, on the bond strength and bond stress-slip curves were discussed. Results suggest that the bond stress-slip curves of push-out RACFST specimens at high temperature differ from those at ambient temperature. Additionally, the bond strength was found to increase with increasing temperature. The bond strength at a high temperature of 800°C is about 3 times higher than that at room temperature. The bond strength can be increased up to 2.6 times after high temperature with the same RAC replacement ratio. Based on the experimental results, regression analysis was conducted to develop a bond strength model to predict the bond behavior between recycled aggregate concrete and steel tube after exposure to high temperatures.