To ensure safety and efficiency of construction and operation of repositories, rock fractures need to be grouted where they intersect the facility. Cement-based grouting materials that have been used extensively in the past may, however, react with the groundwater and produce hyperalkaline leachate. A possible solution for this issue is use of alternative material.

Ethanol/Bentonite Slurry Grouting is another approach to minimize the long-term permeability of rock fractures. The slurry has high fluidity for the case of the ethanol concentration in the liquid phase being 60%. The viscosity of the slurry with bentonite content of 0.4 Mg/m3 was measured for conditions of the shear rate ranging from 0.1 to 1000 1/s. The viscosity of the slurry changed dramatically between the ethanol concentrations of 60 to 40 %, behaving as a non-Newtonian fluid. In order to investigate when the ethanol content of the slurry becomes low enough to achieve sufficient viscosity in rock fractures, an Ethanol Diffusion Test with experimental openings was carried out in the laboratory. Extrapolation of the measured minimum time for the filled slurry to reach the desirable low concentration of ethanol lead to the estimated minimum time ranging from 0.1 hours to 0.7 hours for a 0.2 mm aperture. These facts suggest that the injected slurry flows through the openings of fractures during the early period of injection and, later, as its ethanol content decreases, slurry's viscosity increases sufficiently so that the openings can be blocked.