The effects of silica fume on C3A hydration

Silica fume is a key component of high-performance concrete due to the physicochemical influences on cement hydration and the hardening process. Despite its importance, the effects of silica fume on C(3)A-gypsum systems hydration have been poorly studied. This study was carried out to fill this gap, and results suggested that the hydration was greatly affected by the electrostatic feature of silica fume and the sulfate degree in different systems. In poorly sulfated condition (10 wt% gypsum), silica fume promoted the precipitation of hydrates (monosulfoaluminate and katoite) and chemical shrinkage due to the adsorption of silica fume on the surface of hydrates acting as nucleation seeds. However, in the properly and actually ordinary Portland cement sulfated conditions (30 wt% and 86 wt% gypsum), a delayed precipitation of ettringite was found in silica fume-added samples. An increasing zeta potential result suggested that the negatively-charged silica fume could adsorb the positively-charged Ca-S ion complexes (ascribing to the retardation on C(3)A hydration) and thus weaken the hydration inhibition effect of sulfate on C(3)A and limited the formation of hydrates. It is believed that these findings could fulfill a better understanding of the role of silica fume in modern concrete. (C) 2020 Elsevier Ltd. All rights reserved.