Interaction of Silica Fume and Water Content on Strength and Permeability of Concrete

Two critical factors for improved concrete performance are matrix (cementitious material) and water content. Pozzolanic materials such as silica fume and fly ash are now commonly being added to concrete mixtures to improve performance. This results in complex interaction of pozzolan type/content and water-to-cementitious material ratio on performance. While a relatively small number of data points may be sufficient to arrive at general conclusions, a comprehensive experimental design with sufficient data points and strong statistical tools is needed for development of accurate models to quantify the effect of individual responses. In this experimental investigation, cement was partially replaced with pozzolanic admixture silica fume to achieve improvement in strength and reduced permeability of concrete. Plain Portland cement matrix was partially replaced with silica fume at 5, 10, and 15% by weight. For each silica fume replacement, four different water-to-binder ratios (0.35, 0.3, 0.25, and 0.2) were selected to study their effect and interaction at various levels on compressive strength and permeability. Statistical regression analysis was then performed on the comprehensive experimental data generated in this investigation to develop an empirical model for compressive strength as a function of water and silica fume content. The results indicate that the optimum percentage of silica fume to achieve maximum compressive strength varies with the water content. Also, permeability decreases with increased silica fume content and reduced water. This paper presents the outcome of the comprehensive experimental investigation and statistical analysis to achieve increased strength and reduced permeability in concrete with silica fume.