Synthesis and hydration of alite-calcium sulfoaluminate cement

An alite-calcium sulfoaluminate (ACSA) clinker containing approximately 50% alite and 10% ye'elimite was synthesised at 1300°C using a laboratory furnace and 1% calcium fluoride (CaF₂) as a mineraliser, ground and blended with 5% anhydrite. The hydration mechanism of the resulting ACSA cement was investigated experimentally using quantitative X-ray diffraction and thermogravimetry, as well as by thermodynamic modelling. During the first hours, mainly alite reacts. Ye'elimite starts to dissolve significantly after 2 d, as it is predominately present as inclusions within the alite matrix and thus reacts only after sufficient alite has dissolved to expose the ye'elimite domains within the clinker particles. The main hydration products are calcium–silicate–hydrates (C–S–H), ettringite, monosulfate and portlandite. Mortars prepared using the ACSA cement rapidly develop compressive and flexural strength at early ages corresponding to the fast hydration reactions. It was estimated that the manufacture of this ACSA clinker releases about 11–12% less carbon dioxide than the production of Portland cement clinker.