Synthesis of α′H-belite calcium sulfoaluminate cement from lithium slag: Raw mix design for tailoring clinker mineral phase composition and hydration kinetics

Based on the chemical composition of lithium slag (LMS), a high-belite calcium sulfoaluminate (HB-CSA) clinker containing 18.45% α′ H -C 2 S was synthesized by tailoring the raw mix design. The effects of the basicity coefficient and Al/S̄ ratio on clinker phase assemblage and the subsequent hydration performance of the cement were systematically investigated. The results indicated that adjusting the basicity coefficient and Al/S̄ ratio effectively regulated the phase assemblage and polymorphic composition of the LMS-derived HB-CSA clinkers. Specifically, increasing the basicity coefficient decreased the content of cubic ye'elimite, whereas increasing the Al/S̄ ratio reduced the contents of α′ H -C 2 S and over-burned anhydrite (f-CaSO 4 ). In HB-CSA cement, α′ H -C 2 S and cubic ye'elimite exhibited faster hydration rate than β-C 2 S and orthorhombic ye'elimite, respectively. The enhanced degree of belite hydration promoted the participation of amorphous AH 3 in AFt formation, while the later formation of C-S(A)-H gel and strätlingite progressively filled the capillary pores in the paste, resulting in a steady increase in compressive strength from 43.30 MPa at 1 d to 93.50 MPa at 28 d. Although f-CaSO 4 accelerated the early hydration of HB-CSA cement, excessive amounts inhibited belite hydration and retarded subsequent strength development. These findings provide a new strategy for optimizing the performance of HB-CSA cement and achieving the high-value utilization of LMS.