High temperature behaviour of basalt fibre-steel tube reinforced concrete columns with recycled aggregates under monotonous and fatigue loading

Experimental and numerical investigations were carried out to evaluate the effects of incorporating recycled coarse aggregates (RCA) on the mechanical behaviour of inner steel-tube reinforced concrete columns exposed to high temperature. The specimens were reinforced with basalt fibres (BF) and strengthened by carbon fibre reinforced polymer (CFRP) sheets, which were subjected to mechanical loading in monotonous and cyclic arrangements. Test results show that at room temperature (RT), incorporation of the chopped BF has reduced both the tensile strength and flexural strength of concrete specimens prepared with recycled aggregate concrete (RAC) but not their static elastic modulus. On the other hand, the BF has improved crack resistance of the steel tube reinforced RAC (STRC) column specimens. Also, the reduction in mass and dynamic elastic modulus of BF reinforced STRC specimens are lower than those of STRC at a given RCA replacement ratio and exposure temperature. Furthermore, improvements in mechanical performance under monotonous and fatigue loading was observed for STRC columns reinforced with BF and externally bonded CFRP sheets with high-temperature exposure (HTE). Therefore, it is possible that BF reinforced STRC columns could be used to reduce risk of brittle structural collapse when exposed to fire or elevated temperature.