Natural analogue of interaction between bentonite and concrete

Imai, Jun*

The objective of this research is to understand the 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 32 years. Sample analyses indicated that the original bentonite was Na-type and Ca proportion was increased between the bentonite layers in the range of a few millimeters from the contacting part. On the other hand, the increase of sulfur and the preparation of ettringite (3CaO AlO 3CaSO 32HO) was recognized in the concrete within the depth approximately 20 mm from the contact.