The 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).

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In this report, X-ray photoelectron spectroscopy (XPS) and 29 Si-MAS-NMR was used for the evaluation of deteriorated hardened cement pastes. The deterioration by ammonium 2 nitrate solution was accompanied by changes in the pore structure as well as by structural changes in the C-S-H in the hardened cement paste. The CaO/SiO2 ratio of the C-S-H decreased with the progress of deterioration, there was also polymerization of the silicate in the C-S-H. It was confirmed that the degree of polymerization of silicate of the C-S-H in hardened cement paste can be determined by XPS. It was also shown that the polymerization depends on the structure of the C-S-H.Keywords: Calcium-Silicate-Hydrate (C-S-H)(B); Degradation(C); 29 Si NMR; X-ray photoelectron spectroscopy; CaO/SiO2 ratio 3

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The 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).

There are concerns about the possible increase in the solubility of radionuclides due to the presence of superplasticizers proposed to be added to cementitious materials in a radioactive waste repository. The concentration and molecular weight of a polycarboxylate type SP in hardened cement pastes has been investigated experimentally in this work. The measurement of total organic carbon in both the pore water extracted from hardened cement pastes by compression and the curing water was performed. Organic substances present in pore solution were analyzed to investigate the type and molecular weight of the chemicals. It was found that most SP (more than 90%) remained in the solid phase. Organic substance of a low molecular weight was detected in the pore water by gel permeation chromatography, possibly due to selective adsorption of a high molecular weight part of SP.

High pH conditions of aqueous solutions in a radioactive waste repository can be brought about by dissolution of cementitious materials. In order to clarify the mechanisms involved in maintaining this high pH for long time, we investigated the dissolution phenomena of OPC hydrate.In the present research, leaching tests on powdered cement hydrates were conducted by changing the ratio of mass of leaching water to mass of OPC hydrate (liquid/solid ratio) from 10∼2, 000 (wt/wt). Ordinary Portland Cement hydrate was contacted with deionized water and placed in a sealed bottle. After a predetermined period, the solid was separated from the solution.From the results of XRD analysis on the solid phase and the Ca concentration in the aqueous phase, it was confirmed that Ca(OH) 2 was preferentially dissolved when the liquid/solid ratio was 10 or 100 (wt/wt), and that C-S-H gel as well as Ca(OH) 2 were dissolved when the liquid/solid ratio was 500 (wt/wt) or larger.29 Si-NMR results showed that the silicate anion chain of the C-S-H gel became longer when the liquid/solid ratio was 500 (wt/wt) or greater. This indicates that leaching of OPC hydrate results in a structural change of C-S-H gel.