Ultrasonication and synergistic effects of silica fume and colloidal nanosilica on the C–S–H microstructure

Abstract

This study reports on the effect of ultrasonicating silica fume (SF) and colloidal nanosilica (NS) to fabricate 4 binary (90% cement + 10% SF or 98% cement + 2% NS) and 2 ternary (90% cement + 8% SF + 2% NS) pastes in replacement to Portland cement. The calcium-silicate-hydrate (C–S–H) microstructure is investigated whereas the compressive strength (CS) and porosity data are assessed and discussed. Up to 28 days of hydration the time (t) dependence of the compressive strength (CS vs. t) is fitted using an exponential-like model based on the first order kinetics approximation, from which one extracts the asymptotic C–value and the half-life aging time (th). A significant increase in the asymptotic C–value of the paste while combining ultrasonicated SF and NS is observed at 1 and 3 days, besides presenting the lowest Ca/Si ratio, the highest C–S–H mean chain length and the highest porous structure refinement among all the evaluated pastes at 28 days.