Abstract: Provided are a water-blocking filler, the swelling properties of which do not decrease easily even when in contact with water containing calcium ions, and a filler for engineered multi-barriers with said water-blocking filler as the engineered multi-barrier filler. A water-blocking filler mainly comprising sodium bentonite obtained by mixing 30 weight % or less, in terms of inner percentage, of a pozzolan substance such as fly ash or silica fume with said bentonite, and a filler using said water-blocking filler that is used for engineered multi-barriers in radioactive waste disposal facilities.

Abstract: A concrete pit containing radioactive waste is surrounded by a low diffusion layer of cement-based material, which in turn, is surrounded by a low water permeability layer of sodium-type bentonite and the leaching out of calcium ions from the low water permeability layer is inhibited by mixing sodium bicarbonate or sodium carbonate with the sodium-type bentonite/sand mixture of the low water-permeability layer so that leached calcium ions form a barrier layer having calcium carbonate as the main component in the vicinity of the interface between the layers.

Abstract: Provided are a water-blocking filler, the swelling properties of which do not decrease easily even when in contact with water containing calcium ions, and a filler for engineered multi-barriers with said water-blocking filler as the engineered multi-barrier filler. A water-blocking filler mainly comprising sodium bentonite obtained by mixing 30 weight % or less, in terms of inner percentage, of a pozzolan substance such as fly ash or silica fume with said bentonite, and a filler using said water-blocking filler that is used for engineered multi-barriers in radioactive waste disposal facilities.

Abstract: A cement additive contains industrial waste and has the effect of inhibiting formation of monosulfate in a hardened cementitious material. The cement additive contains specifically calcium carbonate, gypsum and coal ash and/or blast-furnace slag powder. This enables efficient use of industrial waste, allows inhibiting monosulfate formation in the hardened cementitious material, and allows producing a hardened cementitious material having good durability (sulfate resistance).

Abstract: A concrete pit containing radioactive waste is surrounded by a low diffusion layer of cement-based material, which in turn, is surrounded by a low water permeability layer of sodium-type bentonite and the leaching out of calcium ions from the low water permeability layer is inhibited by mixing sodium bicarbonate or sodium carbonate with the sodium-type bentonite/sand mixture of the low water-permeability layer so that leached calcium ions form a barrier layer having calcium carbonate as the main component in the vicinity of the interface between the layers.