Comparison of Two Metakaolins and a Silica Fume Used as Supplementary Cementitious Materials

Synopsis: The performance of two metakaolins as supplementary cementitious materials (SCMs) was evaluated at 8 % by weight cement replacement. The metakaolins varied by their surface area (11.1 vs. 25.4 m2/g). Performance of metakaolin mixtures was compared to control mixtures at water-to-cement ratios of 0.40, 0.50, and 0.60 where no SCM had been used and to mixtures where silica fume had been used as partial replacement for cement. In both mixtures containing metakaolins, compressive, splitting tensile, and flexural strengths increased, as well as elastic modulus, as compared to control mixtures. Setting time was reduced in the pastes with both metakaolins. Additionally, considering durability, both metakaolins reduced rapid chloride ion permeability and expansion due to alkali-silica reaction when compared to control and silica fume mixtures. In general, the finer of the two metakaolins proved more effectiv