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

Abstract

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 TH1p (< 16 ms on average) and Tcp (<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 TH1p 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 TTH1p 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.