¹H — ²⁹Si CPMAS NMR study of the structure of calcium silicate hydrate

This paper presents the results of a systematic ¹H—²⁹Si cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance spectroscopic investigation of single-phase calcium silicate hydrate (C-S-H), and includes variable temperature data. The T^H_1p (< 16 ms on average) and T_cp (<0·6 ms on average) values of both the Q¹ and the Q² Si-sites of C-S-H are much smaller than those of 1·1 nm tobermorite and silica gel. The signal-noise ratios of the CPMAS spectra of C-S-H are also quite low. The T^H_1p values of protons associated with Q₁ (6·48 ms on average) and Q² sites (15·89 ms on average) are significantly different for samples with C/S > 1, and the difference increases with increasing CIS ratio. These results indicate that the protons or proton-bearing species such as OH^- groups and H₂O molecules are in motion at room temperature at frequencies of 10⁴—10⁵ Hz. The different TT^H_1p values are interpreted as indicating that the silicate chain length distribution in the C-S-H samples with CIS > 1 is not unimodal. There are probably many dimers and relatively long chains in the structure.