NMR characterization of hydrates formed in calcium aluminate– silica fume mixtures

Partially deuterated Ca3Al2(SiO4)y(OH)12 4y–Al(OH)3 mixtures, prepared by hydration of Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7) and CaAl2O4 (CA) phases in the presence of silica fume, have been characterized by Si and Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca3Al2(OH)12 and Al(OH)3 phases were detected. From the quantitative analysis of Al NMR signals, the Al(OH)3/Ca3Al2(OH)12 ratio was deduced. The incorporation of Si into the katoite structure, Ca3Al2(SiO4)3 x(OH)4x, was followed by Al and Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of Al MAS–NMR components associated with Al(OH)6 and Al(OSi)(OH)5 environments. The Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C–S–H and C–A–S–H for short. From Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures. & 2008 Elsevier Inc. All rights reserved.