Phase equilibria of hydrated Portland cement

A model is described for predicting the equilibrium phase assemblage in hydrated Portland cement and for calculating the relative contents and composition of phases present in the assemblage, from the chemical composition of the cement and the water/cement ratio. The method is also used to calculate the content of capillary pores using the best available data for the densities for each of the phases. These calculations were carried out on three different Portland cements (two white Portland cements and one grey) at water/cement ratios of 0.70. Energy dispersive spectroscopy (EDS) analysis on the SEM was used to verify the presence of all phases predicted by the model. A density for the C-S-H phase of approximately 2.10 g/cm3 and an evaporable water content in the C-S-H of approximately 19% provided the best agreement between the predicted values of chemical shrinkage, loss of ignition and content of evaporable water, and experimental data. Other results included compositional data on the C-S-H phase corresponding to molar ratios of Al/Ca=0.04 and S/Ca=0.03 in all cements investigated, and Fe/Ca=0.02 in the grey Portland cement.