Thermodynamic properties of Portland cement hydrates in the system CaO–Al2O3–SiO2–CaSO4–CaCO3–H2O

A database is presented for commonly-encountered cement substances including C–S–H, Ca(OH)2, selected AFm, AFt and hydrogarnet compositions as well as solid solutions. The AFm compositions include strätlingite. The data were obtained for the most part from experiment and many of the predicted reactions were confirmed by focussed experiments. The temperature-dependence of the thermodynamic data for the above phases, determined partly from experiment and partly from thermodynamic estimations, are also tabulated in the range 1 °C to 99 °C. Relative to previous databases, sulfate AFm is shown to have a definite range of stability range at 25 °C thus removing long-standing doubts about its stability in normal hydrated cement pastes. Carbonate is shown to interact strongly with stabilisation of AFm across a broad range of temperatures and, at low temperatures, to substitute into AFt. The new database enables the ultimate hydrate mineralogy to be calculated from chemistry: most solid assemblages, the persistence of C–S–H apart, correspond closely to equilibrium. This realisation means that hydrate assemblages can be controlled. The development of a thermodynamic approach also enables a fresh look at how mineralogical changes occur in response to environmentally-conditioned reactions; several papers showing applications are cited.