The objective of this study is to assess the performance of sludge mixed with the commercial grade Portland cement type I for use in minimizing permeability of fractures in rock. The fractures are artificially made in 3 rectangular blocks of sandstone by applying a line load to induce a splitting tensile crack. The water treatment sludge tested comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C) of 1:10, 3:10, 5:10 are suitable with water:cement ratio (W:C) of 1:1 by weight. For S:C = 3:10, the compressive strength and elastic modulus are 1.22 MPa and 224 MPa which are similar to those of bentonite mixed with cement. The shear strengths between the grouts and fractures surfaces are from 0.22 to 0.90 MPa under normal stresses from 0.25 to 1.25 MPa. The S:C ratio of 5:10 gives the lowest permeability. The permeability of grouted fractures with apertures of 2, 10 and 20 mm range from 10–16 to 10–14 m2 and decrease with curing time.

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