Deterioration mechanism of concrete under long-term elevated temperature in a metallurgic environment: A case study of the Baosteel company

A long-term elevated temperature environment is typically found in the metallurgy industry, which has adverse effects on the properties and microstructure of concrete structures. A few studies investigated the effect of short-time high temperature on the properties and microstructure of concrete, but the effect of long-term elevated temperature is seldom analysed. In this study, the deterioration mechanism of concrete under long-term elevated temperature was investigated by determining the thermal stresses on basis of finite element model (FEM) and analyzing the changes in its chemical composition and microstructure through X-ray diffraction (XRD), pore structure analysis (PSA) and scanning electron microscope (SEM). The results indicated that the maximum temperature stress of surface concrete could exceed 4 MPa, which was close to the ultimate tensile strength of normal concrete. The results also showed that calcium hydroxide (CH) could decompose at less than 200 ℃ because of the crystallization of tiny CH crystals, doping with other ions, extended heating time, and xonotlite (α-C2SH), which was formed on the internal surface of the concrete and decomposed on its external surface. Owing to these reasons, cracks and holes were generated, resulting in severe deterioration of the concrete structure.