Effect of alkaline conditions in rocks contacted with shotcrete for 15 years

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  • 15年間吹付コンクリートに接した軽石凝灰岩のアルカリ影響

Abstract

<p>  In radioactive waste disposal facilities, there is concern about the alteration of bentonite in an alkaline condition derived from cementitious materials. In this study, the interaction between shotcrete and pumice tuff for 15 years was investigated in order to understand the formation of secondary phases in alkaline conditions. The results showed that amorphous C-(A-)S-H with a Ca/Si ratio of about 0.7 or slightly richer in Ca and Al was formed in the range of a few mm or a few cm in contact with shotcrete, due to the dissolution of initial amorphous phases such as volcanic glass. The alkali-affected zone of pore water in the rock extends at least 9 cm from the interface, and the porosity and permeability were not changed at depths deeper than a few mm from the interface with shotcrete. It was inferred that the alkali-affected zone was determined by some factors, including groundwater advection. Based on previous findings, it is necessary to consider a transition from C-(A-)S-H to tobermorite in the alkaline alteration reaction of bentonite materials. This study suggested that the transition may take place after a decade under low-temperature conditions such as those in this study site.</p>

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