Modelling long-term evolution of cementitious materials used in waste disposal

This report summarizes the latest developments at SCK•CEN in modelling long-term evolution of cementitious materials used as engineered barriers in waste disposal. In a first section chemical degradation of concrete during leaching with rain and soil water types is discussed. Next we show how the leaching model is coupled with a reactive transport module to determine leaching of cement minerals under diffusive or advective boundary conditions. The module also contains a microstructural model from which hydraulic and transport properties of concrete may be calculated dynamically. This coupled model is simplified, i.e. abstracted prior to being applied to large-scale concrete structures typical of a near-surface repository. Characteristic degradation states of concrete are further linked to distribution ratios that describe sorption onto hardened cement via a linear and reversible sorption process. As concrete degrades and pH drops the distribution ratios are continuously updated. We have thus integrated all major chemical and physical concrete degradation processes into one simulator for a particular scale of interest.