Ettringite instability analysis in the hydration process of the supersulfated cement

The search for new materials to replace Portland cement (PC) has increased due to the high release of carbon dioxide (CO2) and the exploration of raw materials for its production. In this case, supersulfated cement (SSC) appears as an option. SSC consists of up to 90% blast furnace slag and small percentages of calcium sulfate and alkaline activator. This cement has some characteristics similar to PC with the advantage of using less raw material. However, some studies have identified the instability of the ettringite formed in the hydration of SSC although this phenomenon has not been studied in detail in previous research. Therefore, this study aimed to evaluate the behavior of different supersulfated cement compositions, comparing the hydration processes, and identifying the influence of their chemical composition on the instability of ettringite. Microstructural analyses of XRD, TGA, and SEM showed instability of the phases formed from all SSC compositions at 49 days of curing. Mechanical strength and calorimetry analyses showed the best behavior using gypsum as a source of calcium sulfate. Also, the SSC with the highest calcium sulfate content showed lower instability of ettringite and greater compressive strength.