Bond behavior between geopolymer recycled brick aggregate concrete and steel bars after exposure to high temperatures

Abstract

The use of recycled brick aggregate (RBA) as the replacement for natural coarse aggregate in geopolymer concrete is an effective method for waste recycling. When the formed geopolymer recycled brick aggregate concrete (GRBC) is employed in structures, it may encounter the risk of fire. Whether the steel bars and GRBC can work together after a fire is the basis for structural safety and analysis. However, previous research on the bond behavior between GRBC and steel bars after exposure to high temperatures is still lacking. In this paper, pull-out tests on 50 GRBC and 50 ordinary recycled brick aggregate concrete (ORBC) were conducted to investigate the effects of temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C), and RBA replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The test results show that the failure pattern of GRBC specimens changes from splitting-pull-out failure to pull-out failure as the heating temperature increases. The bond strength decreases with the increase of temperature or RBA replacement ratio. When the temperature rises from 200 °C to 800 °C, the bond strength of GRBC pull-out specimens decreases by 11.54 %–72.33 % compared with the specimens at room temperature, and the decrease rate is lower than that of ORBC. The bond strength of GRBC specimens with a 100 % replacement ratio decreases by 46.34 %–53.74 % compared with those without replacement. The peak slip of GRBC specimens generally increases with increasing temperature or decreasing RBA replacement ratio. Based on the post-temperature test results and the room temperature model, suitable models for the bond strength and peak slip of GRBC after high temperatures were established. The predicted results of bond stress−relative slip curves were in good agreement with the test results. The findings of this study can provide a foundation for the application of GRBC, and provide a basis for its structural analysis after high temperatures.