A cement-based grout (90% Type 50, 10% silica fume, 0.4 < water-to-cement ratio, w/c < 0.6) has been used in field trials at AECL's Underground Research Laboratory in Canada and at the OECD/NEA Stripa Mine in Sweden, to evaluate suitable grouts and grouting techniques that could be used for sealing a nuclear fuel waste disposal vault mined deep in granite. Laboratory studies have been carried out to determine the following grout properties: hydraulic conductivity (k); resistance to piping and erosion during setting; influence of grout on the pH and chemical composition of water permeating grouted rock; and the ability of the grout to self-seal after fracturing.
Laboratory tests have confirmed the low intrinsic k of these cement mixtures (10−14 m/s). Using a specially developed cone-in-cone apparatus, we have studied the effect of fracture dilation and temperature changes on the k of thin films of cement. If fractured, the grout has an ability to self-seal and the rate of self-sealing increases with increasing temperature.
The pH and ionic composition of the water permeating grouted fractured granite rock were found to vary with grouted fracture aperture and grout/rock volume ratio. The field tests demonstrated that grout can penetrate and seal very fine fissures (apertures less than 50 μm).