Si NMR Study of the Hydration of Ca3SiO5 and ß‐Ca2SiO4 in the Presence of Silica Fume

Abstract

29 Si magic‐angle spinning nuclear magnetic resonance (MASNMR) was used to study the room‐temperature hydration of C 3 S, ß‐C 2 S, and reactive ß‐C 2 S mixed with different amounts of silica fume (SF) that had been hydrated up to nine months and longer. The overall CaO:SiO 2 molar ratios of the mixes were 0.12, 0.20, 0.35, 0.50, and 0.80. NMR spectroscopy was used to quantify the remaining starting materials and the resulting hydration products of different species. A broad peak assigned to Q 3 , appearing in both the fourier transform (FT) and the cross‐polarization (CP) modes, increased in intensity with increased SF content and with age. This Q 3 species was attributed to two sources: (1) the surface hydroxylation of SF and (2) the cross‐linking of dreierketten (chains of silicate tetrahedra arranged in a repeating three‐unit conformation) in the calcium silicate hydrate (C‐S‐H) structure. A Q 4 species also appeared in the CP spectra of samples with large SF additions after extended hydration and was attributed to cross‐polarization by adjacent hydroxylated Q 3 species at the surface of amorphous SiO 2 .