Effect of calcium source on the phase evolution and hydration of belite-ye’elimite-ferrite clinker: Replacing CaCO3 with CaSO4

Belite-ye’elimite-ferrite (BYF) cement is regarded as a low-carbon alternative to ordinary portland cement. However, the feasibility of using CaSO 4 based industrial waste as the main calcium source to prepare BYF cement is still unclear. The feasibility of synthesizing BYF cement using CaSO 4 instead of CaCO 3 as a calcium source, and its effects on the mineral phase composition and hydration behavior of clinker were explored in this study. Results show that replacing CaCO 3 with CaSO 4 significantly affects the mineral phase transformation, structure, and activity of the target mineral phase in the clinker calcination process. As the CaSO 4 substitution ratio increases, the formation of the C 2 S and ferrite phases are inhibited. The ferrite phases undergo a transformation of C 4 AF → C 2 F → amorphous Fe 2 O 3 .When the substitution ratio is lower than 30 %, the formation of the C 4 A 3 $, C 4 A 3 $-c, and α′- C 2 S is enhanced. This change has a positive impact on the hydration performance of clinker, which is optimal at a substitution ratio of 10 %, with 3d and 28d compressive strengths reaching 45 and 70 MPa, respectively. However, when the substitution ratio exceeds 30 %, excess CaSO 4 fails to fully decompose into CaO, causing insufficient CaO supply, hindering active mineral phase formation and ultimately leading to a marked drop in hydration reactivity. This work demonstrates the feasibility boundaries and reaction mechanism of using CaSO 4 -based industrial wastes as the calcium source for BYF clinker preparation, providing a theoretical basis for high-value utilization of industrial CaSO 4 wastes in low-carbon cement production. • CaSO 4 replaces CaCO 3 as a calcium source were used to prepare BYF cement. • Effects of CaSO 4 on the mineral transformation during clinker calcation were revealed. • Hydaration activity of BYF cement are enhanced when the substitution ratio of CaSO 4 is below 30 %. • Theoretical support is provided for the preparation of BYF cement by utilizing solid waste containing CaSO 4 as raw materials.