Study on construction method of concrete in the underground research laboratory (III)

Iriya, Keishiro*; Mikami, Tetsuji*; Takeda, Nobufumi*; Akiyoshi, Kenji*

The Horonobe underground research laboratory project doesn't carry on only safety assessment study but also demonstration of construction technique upon nuclear waste repositories. Low alkalinity cement is one of candidates for engineered barrier in order to prevent alteration of bentonite and rock by hyper alkaline solution. JNC has developed low alkalinity cement (HFSC) which contains a lot of fly ash, and has studied the physical and chemical properties by laboratory test.Effect on variety of quality of fly ash and monitoring corrosion of rebars in off-shore condition has been studied. In-situ test for actual use of HFSC in constructing the facility was planned. The results are summarized as below. Effects of variety of fly ash upon lower pH are relatively small by testing two type of fly ash and several fly ash content. Variety of fly ash effects properties of fresh concrete but its effect is not significant. And it little effects on mechanical behavior. However, it doesn't effect on properties of shotcrete. Although rebars corrode in HFSC in spite of no intrusion of chloride, increment of corrosion is not significant in half a year until a year. Applicability for structural members is demonstrated by loading test of tunnel concrete segments of HSFC. Pre-mixed HFSC can be supplied by mixing fly ash and silica fume in Sapporo and carry to Horonobe by cement truck.