Hydrate Phase Assemblages in Calcium Sulfoaluminate – Metakaolin – Limestone Blends

The combination of a commercial calcium sulfoaluminate (CSA) cement with metakaolin (MK) and limestone (LS) as supplementary cementitious materials (SCMs) is investigated for a CSA replacement level of 20 wt%. In addition to a pure CSA cement, paste samples have been prepared for three blends with MK to LS ratios of MK/(MK + LS) = 0, 0.5 and 1. All blends used a molar gypsum/ye’elimite ratio of 0.5 and a water to binder ratio of w/b = 0.7. The hydration for the four series has been followed from 1 day to 182 days and the hydrate phase assemblages have been identified using XRD, TGA as well as 27Al and 29Si NMR and compared with predictions from thermodynamic modelling. The results show almost full degrees of reaction for ye’elimite in all blends and that the degrees of reaction for belite and MK have an important impact on the hydrate phases and their quantities formed in the ternary systems.