Evaluating the Suitability of Clayey and Siliceous Limestone for the Synthesis of High-Ye’elimite Calcium Sulfoaluminate-Belite Cement

Calcium sulfoaluminate-belite (CSAB) cement has gained interest as an alternative low-CO2 cement to conventional portland cement (PC) for various applications, offering beneficial properties such as reduced setting time, rapid strength development, and shrinkage compensation. CSAB cement production requires less limestone, lower clinkering temperature, and lower clinker grinding energy compared to PC. The reduced limestone requirement is attributed to the chemical composition of CSAB cement—having lower CaO and higher Al2O3 contents. The surplus limestone rejected by PC plants due to low CaO content presents an opportunity for its use in CSAB clinker production, potentially offering a sustainable approach to alleviate the strain on limestone reserves for future cement manufacturing. This study investigates the suitability of limestones having clayey and siliceous impurities with less than 40% CaO content (by weight) for producing high ye’elimite CSAB cement. The chemical compatibility and scale of utilization of limestone are discussed by comparing the performance of produced cements with a commercial CSAB cement having similar composition. The amount of gehlenite phase was dependent on the free-CaO available for clinkering reactions, restricting the utilization of low-grade limestone to 15%–20%. The experimentally observed phase compositions were found to be in reasonable agreement with the phase assemblage predicted by FactSage modeling. A modified formula for the lime saturation factor was proposed for raw mix proportioning of CSAB clinkers. This study reports the development of laboratory-synthesized CSAB cements of optimal compositions exhibiting similar heat of hydration, microstructure evolution, and strength development as that of commercial CSAB cement.