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Report No.

Natural analogue of alteration of bentonite contacting with concrete

Imai, Jun*

The objective of this research is to make clear long-term alteration processes of bentonite contacting with concrete under a repository condition for radioactive waste. The Uzu tunnel in yamagata prefecture in Japan, constructed during the term of December of 1963 to July 1967, was selected as an appropriate natural analogue: the tunnel wall was made of portland cement and which has been contacting with a bentonite bed during $$geq$$ 32 years. Sample analyses indicated that the original bentonite was Na$$^{+}$$-type and it changed to Ca$$^{2+}$$-type in the range of a few millimeters from the contact. Although a Ca$$^{2+}$$ leaching was also observed from the concrete near the contact, neither transformation to zeolite nor to illite was recognized. On the other hand, sulfur increased and ettringite (3CaO $$cdot$$ Al$$_{2}$$O$$_{3}$$ $$cdot$$ 3CaSO$$_{4}$$4 $$cdot$$ 32H$$_{2}$$O) was recognized in the concrete within the depth about 30 mm from the contact.



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