THERMODYNAMIC AND GEOCHEMICAL MODELLING OF THE ALTERATION OF TWO CEMENT MATRICES

Abstract

The alteration of cernent based materials is a phenomenon of great importance for various radwaste disposal problems, such as the durability of low level waste matrices or engineered barriers.Our approach to the durability of cement is developed along two lines of research: (1) a detailed study of solid-solution interactions by leach tests carried out with two different cement matrices (based on an Ordinary Portland cement and a fly-ash cement). (2) A thermodynamic control and modelling of the alteration processes.An important part of this study has been the selection and the calculation of reliable thermodynamic data for the different compounds constituting such materials. The predictions of geochemical modelling are compared with results of alteration experiments. Fairly good agreement between the geochemical model and experiment is obtained.