How does cement affect the swelling pressure of bentonite? A modelling approach (CI experiment)

The Mont Terri CI experiment (Cement-Clay Interaction) contains interfaces between concrete and MX-80 bentonite, which were sampled after 5 and 10 years of interaction and characterised. Chemical zonations in the hardened cement matrix indicated mineral reactions found in comparable studies (portlandite, calcium silicate hydrate C-S-H, and ettringite dissolution/precipitation). Cristobalite dissolved in the bentonite at the interface, and Mg increased within 1 cm (possible precipitation of a Mg hydroxide high-pH phase). Although pH likely increased in the bentonite, and montmorillonite is unstable at high pH, no indications of montmorillonite dissolution or alterations of its structure was found. The inherently slow dissolution kinetics of clay minerals require unrealistic experimental timeframes and calls for a modelling approach to assess the impact of cement on the bentonite buffer or backfill in a radioactive waste repository.