Preparation of High-Belite Calcium Sulfoaluminate Cement and Calcium Sulfoaluminate Cement from Industrial Solid Waste: A Review

To address the high carbon emissions and resource dependency associated with conventional ordinary Portland cement (OPC) production, this study systematically investigated the preparation processes, hydration mechanisms, and chemical properties of high-belite calcium sulfoaluminate (HBCSA) and calcium sulfoaluminate (CSA) cements based from industrial solid wastes. The results demonstrate that substituting natural raw materials (e.g., limestone and gypsum) with industrial solid wastes—including fly ash, phosphogypsum, steel slag, and red mud—not only reduces raw material costs but also mitigates land occupation and pollution caused by waste accumulation. Under optimized calcination regimes, clinkers containing key mineral phases (C 4 A 3 S − and C 2 S) were successfully synthesized. Hydration products, such as ettringite (AFt), aluminum hydroxide (AH 3 ), and C-S-H gel, were identified, where AFt crystals form a three-dimensional framework through disordered growth, whereas AH 3 and C-S-H fill the matrix to create a dense interfacial transition zone (ITZ), thereby increasing the mechanical strength. The incorporation of steel slag and granulated blast furnace slag was found to increase the setting time, with low reactivity contributing to reduced strength development in the hardened paste. In contrast, Solid-waste gypsum did not significantly differ from natural gypsum in stabilizing ettringite (AFt). Furthermore, this study clarified key roles of components in HBCSA/CSA systems; Fe 2 O 3 serves as a flux but substitutes some Al 2 O 3 , reducing C 4 A 3 S − content. CaSO 4 retards hydration while stabilizing strength via sustained AFt formation. CaCO 3 provides nucleation sites and CaO but risks AFt expansion, degrading strength. These insights enable optimized clinker designs balancing reactivity, stability, and strength.