Influence of Iron on the Structure, Stability, and Hydration of Ye'elimite (Calcium Sulfoaluminate Phase)

ABSTRACT Calcium sulfoaluminate (CSA) cement is a low CO 2 cement having rapid hardening and shrinkage‐compensating characteristics. This study investigates the influence of iron content in the raw mix (5%–20% by weight) on the formation of ye'elimite, the primary phase of CSA cement. Iron is unavoidably present in the raw materials used for CSA clinker production, and its content is increased even more when iron‐rich industrial by‐products are used in the raw mix. While previous studies have reported that iron promotes the stabilization of cubic ye'elimite at the expense of its orthorhombic form, the underlying mechanism remains unclear. In this study, the structural changes in the crystal structure transformation of the ye'elimite phase from orthorhombic to cubic due to the addition of iron are elucidated using density functional theory. Additionally, the effects of iron incorporation on the composition, microstructure, thermal stability, and hydration of ye'elimite are examined. While iron promotes the cubic ye'elimite polymorph, the hydration of iron‐incorporated ye'elimite is influenced by multiple intertwined mechanisms involving structural substitution, proportion of ye'elimite, presence of sulfates, and secondary phases.