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 ۵۰۰ kg/m۳ 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 ۲۱ and ۶۰۰ °C after a curing age of ۹۰ 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 ۷۱.۶۳% from ۷۳.۳۳ GPa at ۲۱°C to ۲۴.۱۲ GPa at ۶۰۰ °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 ۲۱ °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 ۶۰۰ °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.In this laboratory study, a mixed concrete design containing ۵۰۰ kg/m۳ 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 ۲۱ and ۶۰۰ °C after a curing age of ۹۰ 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 ۷۱.۶۳% from ۷۳.۳۳ GPa at ۲۱°C to ۲۴.۱۲ GPa at ۶۰۰ °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 ۲۱ °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 ۶۰۰ °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.

Keywords:

Ordinary Concrete , Heat , Modulus of Elasticity , Hydrated Calcium Silicate (C-S-H) , Calcium Hydroxide (Ca(OH)۲)