Characterization of the Calcium Silicate and Aluminate Phases in Anhydrous and Hydrated Portland Cements by 27Al and 29Si MAS NMR Spectroscopy

Abstract

27Al and 29Si magic-angle spinning (MAS) NMR spectroscopies have proven to be valuable tools for characterization and quantitative analysis of the anhydrous and hydrated calcium silicate and aluminate phases in Portland cements. This paper describes the results obtained in the authors laboratory from the 27Al and 29Si MAS NMR studies of Portland cements during the past few years. A method for quantifying the calcium silicates (alite and belite) in anhydrous and hydrated Portland cements is presented. This employs deconvolution of 29Si MAS NMR spectra combined with the bulk SiO2 content determined from elemental analysis. Direct experimental proof for Al guest-ion substitution in alite and belite and in their hydration products is obtained employing 27A1 MAS NMR. 27A1 quadrupole coupling parameters and isotropic chemical shifts for synthetic samples of the aluminate phase (3CaO Al2O3) and its hydration products (ettringite and monosulphate) are accurately determined from 27Al MAS NMR spectra of the central and satellite transitions. These data are used in 27Al MAS NMR investigations of Portland cements, which provide information about the quantity of the aluminate phase in the anhydrous material, the formation of ettringite during hydration, and the conversion of this phase to monosulphate.