Evolution of a concrete-claystone interface during 17 years of an in-situ experiment (CI): characterisation by high-resolution chemical and mineralogical analysis

Designs for deep storage of radioactive waste foresee cementitious materials as structural elements, backfill or for waste conditioning. Interactions will take place at interfaces of contrasting materials driven by chemical gradients in porewater causing diffusive fluxes of dissolved species. This may lead to mineralogical alterations in the barrier system, which in turn locally influence properties like permeability, swelling pressure or specific retention properties in the case of concrete in contact with claystone or compacted bentonite. The CI experiment (Cement-Clay Interaction) implemented in 2007 in the Mont Terri rock laboratory aims at reducing uncertainties in process understanding related to cement-clay interfaces by providing a detailed analysis of mineralogical changes over relatively long time periods and under realistic boundary conditions. Whereas different types of concrete were examined in contact with Opalinus Clay and compacted MX-80 bentonite, we focus only on the interface between Opalinus Clay and ordinary Portland cement concrete (OPC) and its evolution with time over a period of 17 years. The CI experiment provides a framework for 20 years and is still ongoing.