Reduction in the permeability of plastic concrete for cut-off walls through utilization of silica fume

Principal requirements for plastic concretes used in construction of cut off walls of dams, are a low enough elastic modulus compatible with the surrounding soil, adequate strength for loads sustained and adequate water tightness. Therefore means of reducing permeability without unduly increasing elastic modulus are important areas of research needed in this field. Considering the effectiveness of silica fume in reducing the permeability of normal and high performance concretes, in this research the extent of improvement in impermeability of plastic concrete through utilization of silica fume was investigated. The results obtained showed the substantial effect of incorporation of silica fume in reducing permeability and at the 15% replacement level of cement by silica fume, the coefficient of permeability was reduced 80 times. The utilization of silica fume also increased the strength and elastic modulus of plastic concretes. However the improvement in impermeability was more dominant and by increasing the water to cementitious materials ratio of plastic concrete containing silica fume it was possible to maintain the strength and elastic modulus at the level of control plastic concrete but achieve a 10 times reduction in permeability.