Mäder, UrsUrsMäderJenni, AndreasAndreasJenni0000-0001-7362-5691Lerouge, CathérineCathérineLerougeGaboreau, StephaneStephaneGaboreauMiyoshi, SatoruSatoruMiyoshiKimura, YukinobuYukinobuKimuraCloet, VeerleVeerleCloetFukaya, MasaakiMasaakiFukayaClaret, FrancisFrancisClaretOtake, TsubasaTsubasaOtakeShibata, MasahitoMasahitoShibataLothenbach, BabaraBabaraLothenbach2025-01-082025-01-082017https://boris-portal.unibe.ch/handle/20.500.12422/198923The Cement–Opalinus Clay Interaction (CI) Experiment at the Mont Terri rock laboratory is a long-term passive diffusion–reaction experiment between contrasting materials of relevance to engineered barrier systems/near-field for deep disposal of radioactive waste in claystone (Opalinus Clay). Reaction zones at interfaces of Opalinus Clay with two different types of concrete (OPC and “low-pH”/ESDRED) were examined by sampling after 2.2 and 4.9 years. Analytical methods included element mapping (SEM, EPMA), select spot analysis (EDAX), 14C-MMA impregnation for radiography, and powder methods (IR, XRD, clay-exchanger characterisation) on carefully extracted miniature samples (mm). The presence of aggregate grains in concrete made the application of all methods difficult. Common features are a very limited extent of reaction within claystone, and a distinct and regularly zoned reaction zone within the cement matrix that is more extensive in the low-alkali cement (ESDRED). Both interfaces feature a de-calcification zone and overprinted a carbonate alteration zone thought to be mainly responsible for the observed porosity reduction. While OPC shows a distinct sulphate enrichment zone (indicative of ingress from Opalinus Clay), ESDRED displays a wide Mg-enriched zone, also with claystone pore-water as a source. A conclusion is that substitution of OPC by low-alkali cementitious products is not advantageous or necessary solely for the purpose of minimizing the extent of reaction between claystone and cementitious materials. Implications for reactive transport modelling are discussed.en500 - Science::550 - Earth sciences & geologyarticle10.7892/boris.9608710.1007/s00015-016-0240-5