Evaluation of diffusion coefficients of chloride ion in hardened high-volume fly ash silica fume cement pastes

Mihara, Morihiro  ; Torii, Kazuyuki*

In order to evaluate a long-term behavior of hardened high-volume fly ash silica fume cement paste, HFSC, which is considered to be used as filling and structural materials in a repository for the radioactive waste disposal, apparent diffusion coefficients of chloride ion were obtained which might diffused from the surrounded groundwater into the cementitous material. The profiles of chloride concentration in hardened cement paste after the immersion of sodium chloride and calcium chloride solution were measured by electron probe microscopy analysis and apparent diffusion coefficients were calculated fitting these profiles. And, effects of mixture proportion of fly ash content, 40%, 30% and 20%, in HFSC and period of diffusion experiment, 28days and 91days, on the apparent diffusion coefficient were studied from the view point of the pore structure and immobilization ability of chloride ions in HFSC. It was found that the diffusion coefficient of HFSC using 40% of fly ash, HFSC424, was the smallest value in the cement pastes used and the apparent diffusion coefficient degreased as the experimental period. Although HFSC424 had a larger porosity and lower immobilization ability of chloride ion than ordinary Portland cement, it was concluded that the smallest diffusion coefficient was caused by the fine and discontinuous pore structure of HFSC424.