Stress-strain Constitutive Relation and Residual Strength Evaluation of Concrete After Being Subjected to High Temperatures and Spray Cooling

In order to further reveal the influence of aggregate type on the performance of concrete under axial compression after being subjected to high temperatures and spray cooling, uniaxial compressive strength tests of concrete after being subjected to different fire temperatures and spray cooling were carried out on standard prismatic specimens of ordinary concrete, high-strength concrete, and recycled aggregate concrete. The stress-strain curves during the whole axial compression process were obtained. The effects on the peak stress, peak strain, elastic modulus of three kinds of concrete specimens and their damage process after being subjected to high temperatures and spray cooling were compared and analyzed. The test results showed that:after being subjected to high temperatures and spray cooling, the cracks of high strength concrete surface developed earlier and faster; the peak point of recycled aggregate concrete curve moved to the right most obviously as temperature increased, and the peak point of high strength concrete curve decreased the least; with the increase of temperature, the peak stress of ordinary concrete decreased most obviously, the peak strain of recycled aggregate concrete increased the most; the elastic modulus of high-strength concrete decreased least after being subjected to high temperatures and spray cooling. With the increase of temperature, the difference of damage development of recycled aggregate concrete was the most significant, while the energy consumption was the lowest. Based on the test results, the strength evaluation formulas and uniaxial stress-strain constitutive equation of different concrete after being subjected to different fire temperatures and spray cooling were put forward, and the calculated values were in good agreement with the actual values.