On the early hydration of cubic ye'elimite: New insights from time-resolved in situ MAS NMR spectroscopy

Two polymorphs of ye'elimite are known to exist in calcium sulfoaluminate cements, namely, orthorhombic (iron free), C4A3$ and cubic/pseudo-cubic (iron incorporated), C4A3-xFx$ forms. The very early hydration behaviour of cubic ye'elimite (nominal composition: Ca3.8Na0.2Al5.6Fe0.2Si0.2O12SO4) has been investigated using a time-resolved in situ multi-nuclear (1H, 27Al, 23Na and 29Si) MAS NMR spectroscopic approach. The study shows that the reaction pathway and the intermediate species formed are substantially different from those that are observed during the hydration of orthorhombic ye'elimite, and the rate as well as the nature of hydration products are dictated by the presence or the absence of limestone (CaCO3). Furthermore, the detection of diverse transient species as well as the uncovering of different kinetic behaviour during the early hydration of cubic ye'elimite illustrate the advantages of time-resolved in situ MAS NMR experimental approach for fingerprinting hydrated phases.