Post-fire compressive performance of basalt fiber recycled aggregate concrete filled steel tube

This study reports the results of post-fire axial compressive tests on 87 basalt fiber recycled aggregate concrete (BFRAC) cubes and 25 basalt fiber recycled aggregate concrete filled steel tube (BF-RACFST) short columns. The variables were temperature (20, 300, 500, and 800 °C), recycled aggregate replacement ratio (0, 50, and 100 %), basalt fiber content (0, 4, and 8 kg/m³), and cooling method. The specimens were firstly heated at constant high temperatures. After cooling to room temperature, the axial compression tests were conducted. The findings revealed that recycled aggregate prevented explosive spalling of BFRAC but reduced the post-fire capacity and stiffness of BF-RACFST. Adding basalt fiber increased the compressive strength of BFRAC cubes, decreased BF-RACFST post-fire capacity, and slightly increased the post-fire compressive stiffness of the short columns. After cooling in water, the load and failure capacity of BF-RACFST were lower than those of natural cooling. Since structures are employed in the elastic phase under normal working conditions, adding basalt fiber can compensate for the compressive stiffness loss caused by recycled aggregate in concrete filled steel tubes after high temperatures. However, the reduction in capacity safety reserves should be considered when designing and post-fire repairing. If circumstances allow, rapid cooling methods, such as water cooling, should be avoided during fire extinguishing to reduce structural strength loss. Eventually, a design model was built to calculate the residual strength, compressive stiffness, and peak strain of the post-fire BF-RACFST short columns.