THE INFLUENCE OF SILICA FUME ON THE COMPRESSIVE STRENGTH OF CEMENT PASTE AND MORTAR

The compressive strengths of silica fume cement paste and mortar were evaluated at various water-cementitious ratios. Five different water-c ementitious ratios were used including, 0.22, 0.25, 0.28, 0.31, and 0. 34 and two contents of silica fume, 16% and 25% by weight of cement. S uperplasiticizer content was adjusted for each mix to ensure that no s egregation would occur. The results show that the increase in compress ive strength of mortar containing silica fume, as a partial replacemen t for cement, greatly contributes to strengthening the bond between th e cement paste acid aggregate. Partial replacement of cement by silica fume and the addition of superplasticizer increases the strength of m ortar but has no influence on the strength of cement paste. Results we re verified by statistical analysis using hypothesis testing at a 95% confidence level. It was also demonstrated that superplasticizer in co mbination with silica fume plays a more effective role in mortar mixes than in paste mixes. This can be attributed to a more efficient utili zation of superplasticizer in the mortar mixes due to the better dispe rsion of the silica fume particles. The paper also reviews some of the available literature on the influence of silica fume on cementitious composites and unsettled questions associated with this topic.