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Mineralogical Changes of Cement and Bentonite Accompanied ith Their Interactions

Published online by Cambridge University Press:  15 February 2011

Seiichi Hoshino ,
Tetsuji Yamaguchi ,
Toshikatsu Maeda ,
Masayuki Mukai ,
Tadao Tanaka  and
Shinichi Nakayama
Seiichi Hoshino
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Tetsuji Yamaguchi
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Toshikatsu Maeda
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Masayuki Mukai
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Tadao Tanaka
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Shinichi Nakayama
Affiliation:
Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
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Abstract

Mineralogical changes of cement and bentonite accompanied with their interaction wereexperimentally studied by mixing granulated hardened cement paste and bentonite, and aging the mixture for91 days at 50° C. Mineralogical changes of cement and bentonite were identified by XRD. Hydratedcalcium-silicate phases (C-S-H), Ca(OH)2, ettringite and monosulfate were identified in the unalteredhardened cement. While Ca(OH)2 and monosulfate decreased with aging and disappeared after 91 days,calcite and katoite (Ca3Al2(SiO4)(OH)8) were formed concurrently. Montmorillonite, quartz (and/orchalcedony), clinoptilolite, plagioclase, calcite, analcime and pyrite were identified in the unaltered bentonite.The XRD pattern showed that diffraction intensities of these minerals decreased with aging. It seems thatthese primary minerals dissolved in the course of the alteration. C-S-H appeared in bentonite during the agingas secondary phases, indicating the participation of silicon dissolved from the bentonite and calcium from thecement formed the C-S-H. The formation of C-S-H that had been predicted by previous modeling studieswas confirmed by the present experiments.

In addition, diffusivity of tritiated water in mixed specimen with granulated hardened cement andbentonite was determined by a through-diffusion method. The effective diffusivity of tritiated water decreasedwith aging. The result suggests that the mass diffusivity in the interface of cement-bentonite system willdecrease with their interactions. The results of the diffusion experiments are qualitatively consistent with thediffusivity change in cement-bentonite systems predicted by some computational studies.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1193: Scientific Basis for Nuclear Waste Management XXXIII , 2009 , 445
Copyright
Copyright © Materials Research Society 2009

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