High Temperature Resistance of High-Content Limestone-Modified Sulfoaluminate Cement

The high temperature resistance of ordinary portland cement concrete has obvious limitations and is an important issue affecting the safety of concrete structures. A kind of high temperature resistant cement was obtained by modifying sulfoaluminate cement with a large amount of limestone in this paper, which can better cope with the high temperature cracking of concrete caused by fire. After high temperature treatment at 200°C, 400°C, 600°C, 700°C, and 800°C, the macroscopic properties such as mass loss and strength of cement specimens were tested, respectively, and the microscopic characteristics of cement specimens were analyzed by XRD, SEM, DSC-TG, and MIP. The results show that with the increase of temperature, the strength of the new cement can maintain a relatively stable state in the temperature range of 600°C, because its phase composition is primarily composed of calcium carbonate, and the hydration products of the multicomponent system supplemented by ettringite, AH3, and calcium carboaluminate are gradually transformed into calcium carbonate during the heating process; Calcium carbonate slowly decomposes after 650°C, forming CaO and discharging a large amount of CO2. The mass and strength of the cement specimen are significantly reduced. The strength is only 43% of the initial strength at 800°C, but it can be self-repaired in the environment of appropriate amount of water and high concentration of carbon dioxide; MIP and SEM results show that there are a large number of through holes inside cement specimen, which can timely discharge water vapor in the high temperature environment to avoid cracking caused by excessive vapor pressure. Therefore, this kind of cement with calcium carbonate as the main internal component, its internal calcium carbonate performance is closer to the thermal properties of concrete aggregates, which helps to improve the high temperature resistance of cement.