investigation of the effect of high temperature on the microstructure of conventional concrete containing high grade of portland cement

In this laboratory study, a mixed concrete design containing 500 kg/m3 portland cement was prepared, and elastic modulus testing, x-ray diffraction (xrd) analysis, and scanning electron microscope (sem) image analysis were performed on concrete samples at 21 and 600 °c after a curing age of 90 days to investigate and evaluate the microstructure of concrete at room temperature and under high temperature. the results of the tests indicate that high temperature causes a decrease in the results, so that the elastic modulus of concrete experienced a decrease of 71.63% from 73.33 gpa at 21°c to 24.12 gpa at 600 °c, and in the xrd analysis, a decrease in the height of the peaks of hydrated elements is observed. the low peak height of calcium hydroxide in the xrd spectrum indicates a proper polymerization process in conventional concrete. in sem analysis, at a temperature of 21 °c, due to the completion of a large part of the polymerization process, the tree structure, pores and unhydrated particles are seen in their minimum amount, but after applying a temperature of 600 °c to the concrete sample, with damage to the microstructure of the concrete and the hydrated calcium aluminum sulfate (c-a-s-h) and hydrated calcium silicate (c-s-h) gels, an increase in the tree structure, pores and cracks is evident in the concrete sample.