Preparation and Properties of Sulfur-Modified Alite Calcium Sulfoaluminate Cement

Alite calcium sulfoaluminate (ACSA) cement is an innovative and environmentally friendly cement compared to ordinary Portland cement (OPC). The synthesis and hydration of ACSA clinkers doped with gradient sulfur were investigated. The clinker compositions and hydrated pastes were characterized by X-ray diffraction (XRD), isothermal calorimetry, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) to analyze its mineral contents, hydration products, heat release, pore structure, and microstructure. The compressive strength and linear expansion of ACSA mortars were tested for their mechanical properties. Results showed that clinkers doped with 2 wt.% MgO can offset the hurdle that SO3 caused to the formation of C3S (tricalcium silicate). Clinkers with varying ratios of C3S and C(4)A(3)$ (calcium sulfoaluminate) were obtained, achieving 58-70% C3S and 2.0-5.6% C(4)A(3)$ in ACSA through adjusting the KH (lime saturation factor) values and SO3 dosage. ACSA cement showed better early mechanical properties. The 0.93 KH value with 3% SO3 dosage in the raw meal, which contains 63.9% C3S and 2.98% C(4)A(3)$ in the clinker, reached an optimal compressive strength level at 1d (26.35 MPa) and at 3d (39.41 MPa), marking 30.45% and 18.70% increases compared to PII 52.5. The excellent early strength of ACSA cement may offer promising applications t increasing the incorporation of supplementary cementitious materials, thereby reduce pollution and carbon emissions.