Si-29 NMR study of the hydration of Ca3SiO5 and beta-Ca2SiO4 in the presence of silica fume

Si-29 magic-angle spinning nuclear magnetic resonance (MASNMR) nas used to study the room-temperature hydration of C3S, beta-C2S, and reactive beta-C2 S mixed with different amounts of silica fume (SF) that had been hydrated u p to nine months and longer, The overall CaO:SiO2 molar ratios of the mixes were 0.12, 0.20, 0.35, 0.50, and 0.80, NMR spectroscopy was used to quanti fy the remaining starting materials and the resulting hydration products of different species. A broad peak assigned to Q(3), appearing in both the fo urier transform (FT) and the cross-polarization (CP) modes, increased in in tensity with increased SF content and with age. This Q(3) species was attri buted to two sources: (1) the surface hydroxylation of SF and (2) the cross -linking of dreierketten (chains of silicate tetrahedra arranged in a repea ting three-unit conformation) in the calcium silicate hydrate (C-S-H) struc ture. A Q(4) species also appeared in the CP spectra of samples with large SF additions after extended hydration and was attributed to cross-polarizat ion by adjacent hydroxylated Q(3) species at the surface of amorphous SiO2.