THE EFFECT OF THE CALCIUM LEACHING ON CAPACITY FOR CHLORIDE ION BINDING OF THE HARDENED CEMENT PASTE

Cement based materials such as the concrete are used as barriers of the radioactive waste disposal facilities. As for the cement based materials, the capacity for binding of the radionuclide is required in facilities, and the ability to control the leak of the nuclide to the external environment is also expected by the low diffusivity of cement based materials. The transport of radionuclide has to be controlled leakage to the external environment in the radioactive waste disposal facilities during 10,000 years. Therefore, the appropriate design of the radioactive disposal facilities is necessary, and the accurate mass transfer prediction model that considered the calcium leaching of cement based materials with the order for tens of thousands of years to evaluate it safely is necessary. In the current model, there is a difference between measurement and predicted value of chloride ion ingress as simulated a nuclide movement in the calcium leaching region of hardened cement paste. It is considered that the input parameter for the capacity for binding of the chloride ion of the hardened cement paste in calcium leaching region is not appropriate. The purpose of this study is to clarify the capacity for the binding of the hardened cement paste that calcium leaching occurred quantitatively. In the experiment, ammonium nitrate solution was used to accelerate calcium leaching of the hardened cement paste. The hardened cement paste with different composition by changing the immersion period was produced. The capacity for binding of the chloride ion by immersing the sample in NaCl solution was determined. In addition, the mineral composition of hardened cement paste was determined by the powder X-ray diffraction with Rietveld method, and the chemical bonding state of the silica chain of calcium silicate hydrate (C-S-H) was measured by a solid nuclear magnetic resonance device (NMR) to clarify the mechanism that quantity of chloride ion adsorption changed. The results in this study are followings. As immersion period became long, the CaO/SiO₂ ratio of C-S-H in sample which immersed in ammonium nitrate solution decreased, and the capacity for chloride ion binding of leached sample also decreased. As for this reason, the decrease of the adsorption site by the polymerization of silica chains in C-S-H was suggested by the results obtained from NMR measurement, and monosulfate which was one of the hydrates in hardened cement paste was disappeared by calcium leaching. The capacity for chloride ion binding of hardened cement paste was formulated by the results of experiments, and it was able to estimate the predicted value with less than 25％ of errors.硬化セメントペーストからのカルシウム溶脱に伴うC-S-Hの劣化を考慮した物質移動特性変化について基礎的な知見を得ることを目的とし、促進溶脱試料を用いセメントペーストのカルシウム溶脱に伴うC-S-HのCaO/SiO₂の変化、Si鎖の化学状態及びC-S-Hの塩化物イオン吸着能力の変化について検討を行った。この結果、溶脱に伴うC-S-HのCaO/SiO₂の低下と吸着能力には相関関係があることが確認できた。また、この相関関係を用い、異なるCaO/SiO₂のC-S-Hの塩化物イオン吸着量を推定できる式を提案した。