Modelling of chemical degradation of blended cement-based materials by leaching cycles with Callovo-Oxfordian porewater

- A thermodynamic model is used to simulate chemical degradation of blended cement by interaction with COx porewater at 25 °C.
- The stepwise evolution of the CEM-V microstructure under COx porewater leaching is described.
- The evolution of major species is compared against experimental data with good results.
- ThermoChimie v.9.0.b database proves to solve with high degree of success complex (cementitious-clayey) systems.
- The model allows predictions on the pore solution of degraded state for any type of cement-based materials.

The present work describes a thermodynamic model based on pore water replacement cycles to simulate the chemical evolution of blended cement (BFS + FA) by interaction with external Callovo-Oxfordian (COx) pore water. In the framework of the radioactive waste management, the characterization of the radionuclide behaviour (solubility/speciation, adsorption) in cementitious materials needs to be done for several chemical degradation states (I to IV). In particular, in the context of the deep geological radioactive waste disposal project (Cigéo), cement-based materials will be chemically evolved with time in contact with the host-rock (COx formation). The objective of this study is to provide an equilibrium solution composition for each degradation state for a CEM-V cement-based material to support the adsorption and diffusion experiments reproducing any state of degradation. Calculations have been performed at 25 °C using the geochemical code PhreeqC and an up-to-date thermodynamic database (ThermoChimie v.9.0.b) coupled to SIT approach for ionic strength correction. The model replicates experimental data with accuracy. The approach followed in this study eases the analysis of the chemical evolution in both aqueous and solid phase to obtain a fast assessment of the geochemical effects associated to an external water intrusion of variable composition on concrete structures.