A study of the hydration of aluminate minerals based on the measurements of the mean and the variance of the proton magnetic resonance relaxation rate

Mean longitudinal proton relaxation rates and their variances were measured in hydrated mono- and tricalcium aluminates. The results were analysed using a two-site model of bulk and adsorbed water. A formalism for the calculation of the fractions of water in these states and of the relaxation rate in adsorbed state was developed. A significant release of water from the adsorption layer occurred at about 400-500 min after hydration of the monocalcium aluminate. The relaxation rate of water protons in the adsorbed state increased continuously during the cement hydration (up to 1200 min). During the induction period this increase is attributed to the growing viscosity of the bulk liquid and to the nucleation. During the later stages of hydration the rate increase is explained by the diminishing number of adsorption layers. The maximal values of the relaxation rate in the adsorption layer of monocalcium aluminate indicated the monomolecular adsorption. The hydration of tricalcium aluminate was characterised by higher initial and lower final (t(hydr) = 1100 min) values of the relaxation rate in the adsorbed state, After about 500 min of hydration the fraction of adsorbed water molecules and the relaxation rate in the adsorbed state reach a maximum.