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In situ experiments at Atomic Energy of Canada Limited’s Underground Research Laboratory have demonstrated that a specially developed high-performance cement-based grout, called the reference grout, consisting of 90% sulphate-resistant cement (Canadian Type 50), 10% silica fume (SF) and superplasticizer can seal very fine fissures in granitic rock. Studies are now in progress to determine the longevity of these materials. This paper describes progress in studies of the hydraulic conductivity (i.e. coefficient of permeability), K, of the grout at water/cementitious materials ratios, w/c, between 0.4 and 0.8. The K was assessed with the grouts under compressive and tensile stress using specially designed radial flow permeameters. The results confirm that the K of the reference grout is two to three orders of magnitude lower than that typically observed for intact granite rock (10−12 m/s). Moreover, the data show that adding silica fume and reducing the w/c decreases K. The hydraulic conductivity data coupled with field work and other laboratory data strongly suggest that the reference grout can be successfully used to seal finely fractured rock in the vicinity of a nuclear fuel waste disposal vault.

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