CALPHAD formalism for Portland clinker: thermodynamic models and databases

The so-called CALPHADmethod is widely used in metallurgy to predict phase diagramsof multi-component systems. The application of the method to oxide systems is much more recent, mainly because of the difficulty of modelling the ionic liquid phase. Since the 1980s, several models have been proposed by various communities. Thermodynamic databases for oxides are available and still under development. The purpose of this article is to discuss the distinct approaches of the method for the calculation of multi-component systems for Portland cement elaboration. The article gives a state of the art of the most recent experimental data and the various calculations for the CaO–Al2O3–SiO2 phase diagram. A literature review of the three binary sub-systems leads to main conclusions: (i) discrepancies are found in the literature for the selected experimental data, (ii) the phase diagramdata in the reference books are not complete and up to date and (iii) the two-sublattices model and the modified quasichemical model can be equally used for the modelling of the aluminates liquid. The predictive feature of the CALPHADmethod is illustrated using the CaO–Al2O3–SiO2 system with the two-sublattices model: extrapolated (predicted) and fully-assessed phase diagramsare compared in the clinkering zone of interest. The recent application of the predictive method for the calculations of high-order systems (taking into account Fe2O3, SO3, CaF2, P2O5,…) shows that the databases developed with the two-sublattices model and the modified quasichemical model are no longer equivalent.