A new methodology for thermodynamic data refinement: Bracketing of reactions among cement phases by water activity changes
Résumé
Thermodynarnic data on various types of phases are detemined by calorimetric or ab initio methods and their knowledge is subject to uncertainty. The construction of phase diagrams from this information can lead to very different results depending on the values taken for the data within the uncertainty range. One way to further constrain the data is to make them inter-coherent ("data refinement"), asking them to comply with the addition al constraints provided by phase equilibria. The usual method is to bracket the reactions by temperature and pressure variations. Here, we propose to deterrnine the position of equilibria by varying activities of chemical constituents. The method is applied to reactions between cement phases by varying the water activity; the variation is obtained by adding CaCl2 to the experimental runs. The prediction of reactions and the role of water activity can be visualized by use of "Zen + k" software; the prediction of the values of water activity depending on the amount of added CaCl2 is computed by "Arxim" software. Preliminary data are presented and the new methodology is compared to the standard one.