Ternary blending with metakaolin and silica fume to improve packing density and performance of binder paste

Abstract

In theory, ternary blending of cement with metakaolin (MK), which is of finer size, and silica fume (SF), which is even finer, would improve the packing density (PD) by successively filling the voids between cement grains. This should release more excess water (water in excess of that filled into voids) for fresh properties improvement and densify the microstructure for hardened properties improvement. To verify this postulation and reveal how and why (cement + MK + SF) ternary blending improves the fresh and hardened properties, 21 binder pastes with various MK and SF contents and a constant water/binder ratio were produced for flowability, adhesiveness, strength, sorptivity and porosity testing and microstructure observation, and the corresponding binder mixes were produced for PD measurement. The results showed that such ternary blending could improve the PD and both the fresh and hardened properties. In-depth analysis proved that the additions of MK and/or SF exerted influence through the eventual changes in PD and water film thickness (WFT). Lastly, plots depicting the concurrent flowability-strength and flowability-durability performances are produced to help find the optimum MK and SF contents for best overall performance.