Axial compressive behavior of basalt fiber reinforced polymer-confined damaged concrete after exposed to elevated temperatures

An experimental study on the axial compressive behavior of 36 elevated temperature damaged and 15 unheated concrete cylinders wrapped with basalt fiber reinforced polymer(BFRP) sheets was conducted. The test results show that confinement can significantly change failure mode, improve the strength and ductility of elevated temperature damaged concrete cylinders. After confined with two layers of BFRP sheets, the strength of the cylinders damaged by 200℃, 400℃, 600℃ and 800℃ increases by 56%, 82%, 234% and 250%, respectively; And the axial deformation increases by 328%, 198%, 232% and 136%, respectively. The typical ultimate stress models and ultimate strain models for FRP-confined undamaged concrete are not suitable for confined elevated temperature damaged concrete cylinders. Based on the test results, variables for calculation of ultimate stress and ultimate strain are determined, and ultimate stress model and ultimate strain model of confined elevated temperature damaged concrete cylinders are proposed.