Borate retardation of cement set and phase relations in the system Na₂O—CaO—B₂O₃—H₂O

The CaO-rich portions of this system have been determined at 25° and 55°C. Twenty-one closely spaced compositions were prepared from analytical reagent-grade materials and reacted in sealed containers for up to 6 months. Solid phases were characterized mainly by X-ray diffraction and the aqueous phase was analysed chemically for Ca, Na and B. Solubility data were also obtained from singlephase preparations of selected hydrates; in conjunction with data in the literature, extensive thermodynamic modelling of solubility relations was undertaken. The combination of calculation and experimental determinations enabled the equilibrium features to be determined rapidly; cross-checks between calculated and experimental data are presented.