Physico-chemical investigation of clayey/cement-based materials interaction in the context of geological waste disposal: Experimental approach and results

Within the concepts under study for the geological disposal of intermediate-level long-lived waste, cement-based materials are considered as candidate materials. The clayey surrounding rock and the cement-based material being considered differ greatly in their porewater composition. Experiments are conducted on the diffusion of solutes constituting those porewaters in a confined clay/cement composite system using cells. The test temperature was set at 25 °C and 2, 6 and 12 months. Results supply new information: carbonation is low and not clog the interface. Such absence of carbonation allows for the diffusion of aqueous species and, thus, for the degradation of the cement paste and the illitisation of illite/smectite interstratifications. The cement material is subjected to a decalcification: portlandite dissolution and a CaO/SiO₂ reduction in the calcium silicate hydrate. The sulphate in diffusion induces non-destructive ettringite precipitation in the largest pores. After 12 months, about 800 µm of cement material is concerned by decalcification.