Si-29 isotopic enrichment was used for acquisition of multiple Si-29 magic-angle spinning (MAS) and cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra, in situ in an NMR probe, from a single sample of hydrating Ca3SiO5 (C3S). Data with excellent signal-to-noise ratios were obtained at 20, 50 and 75-degrees-C, with minimal use of spectrometer time, and without the need for the quenching of multiple samples. Spectral line widths and polymer-chain lengths derived from the spectra had no detectable differences from experiments in which the quenching was carried out with propan-2-ol. Furthermore, the effects of the MAS technique on the hydration reaction appeared to be minimal. At 20-degrees-C, the bulk hydrate initially produced was dimeric; at later stages of the reaction, polymerization occurred. Arrhenius energies of 35 and 100 kJ mol-1, respectively, were calculated for these two reactions. The cross-polarization (CP) spectra acquired throughout the hydration showed that at 20-degrees-C, 2% of the hydrated monomeric Q(O)(H) Species persisted from after the induction period through to the late stages of the hydration reaction; this indicates that this species is unlikely to result from surface hydroxylation of C3S; an upfield shift of this species occurred with increasing hydration, indicating a possible change of environment for the silicate species. The amount of Q(O)(H) produced was found to increase at higher temperatures. Potential mechanisms for polymerization were assessed and a model in which dimeric-silicate units are linked together by insertion of monomers (dimer --> pentamer --> octomer) was found to give the best fit to the observed data; these results support a dreierketten model for the structure of the hydrate.
