Synergistic effects of CuO and CaF2 additives in facilitating low-temperature tricalcium silicate formation and stabilization

• CaF₂ promotes M 1 alite formation, while CuO shifts alite to the M 3 polymorph. • Significant alite content achieved at 1200°C with combined CuO-CaF₂ additives. • CuO and CaF₂ co-addition enhances alite formation at low firing temperatures. • Co-addition of CuO and CaF₂ lowers energy demands in clinker production. This study investigates the effects of CuO, CaF₂, and their combination on phase formation in C₃S (alite) clinkers at different firing temperatures, aiming to reduce energy consumption in clinker production. Clinker samples with 0.1 wt.% CuO, 0.8 wt.% CaF₂, and a combination of 0.1 wt.% CuO and 0.8 wt.% CaF₂ were synthesized and fired at temperatures between 1200°C and 1350°C. The mineralogical composition of the clinkers was analyzed using X-ray diffraction patterns with Rietveld refinement technique. The results showed that alite formation was absent below 1350°C in clinkers without additives. The addition of CuO promoted belite (C₂S) formation and reduced free lime content but did not significantly induce alite formation. In contrast, CaF₂ significantly enhanced alite formation, yielding monoclinic M 1 and M 3 polymorphs, with M 1 being the dominant phase. The addition of 0.8 wt.% CaF₂ accelerated alite phase content of 18.96 wt.% at 1200°C, which further increased to 73.54 wt.% at 1350°C. The combined addition of CuO and CaF₂ further improved alite formation at lower temperatures, with alite content higher than 50 wt.% at 1250°C. These findings demonstrate that CuO and CaF₂ act synergistically to facilitate alite formation at reduced firing temperatures, providing a potential pathway for energy-efficient clinker production.