Step-by-step observation of the hydration of C3S by magic-angle spinning 29Si nuclear magnetic resonance: the masking effect of D2O

High-resolution solid-state ²⁹Si nuclear magnetic resonance (NMR) characterization of hydrated C₃S provides a means of selectively observing the hydrogen-containing phases. In particular, by applying the cross-polarization (CP) technique, we demonstrated that a contrast can be obtained, not only for hydrated against anhydrous phases, but also for hydrogen-hydrated against deuterium-hydrated phases. Selectively deuterated samples were thus prepared by a H₂O/D₂O alternated hydration procedure. The progress of the polycondensation of orthosilicates as derived by H₂O was followed, demonstrating that a separate microphase of anhydrous C₃S prevailingly reacted at any step. An induction period, showing a low reactivity and mainly formation of Q^o hydrated was observed during the first hydration steps of selectively deuterated samples. The efficiency of the masking effect of D₂O was also indirectly proven by comparison with calorimetric measurements.