Fingerprinting the hydration products of hydraulic binders using snapshots from time-resolved in situ multinuclear mas nmr spectroscopy

The very early hydration behavior of a hydraulic binder phase, ye'elimite, Ca4Al6O12SO4, in the absence and in the presence of calcium sulfate, has been investigated. A time-resolved in situ multinuclear magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic suite involving 1H and 27Al MAS as well as two-dimensional 27Al multiple quantum MAS (MQMAS) experiments has been employed to detect the transient species and to govern the sequence of hydration reactions and the subsequent formation of the hydration products. The results of the study show that the rates of formation of ye'elimite hydration products vary substantially according to the absence or the presence of calcium sulfate. Hydrated calcium sulfoaluminate phases such as ettringite and monosulfate as well as aluminum hydroxide gel have been detected during the various stages of hydration. The direct observation of various transient species during the hydration stages of calcium aluminates and calcium sulfoaluminates illustrates the potential of a newly designed time-resolved in situ 1H MAS NMR experimental approach for fingerprinting phases and offers significant advantages over other established techniques in detecting transient species.