Activity of silica fume and dealuminated kaolin at different temperatures

Abstract

Silica fume (SF) and dealuminated kaolin (DK) were investigated for their pozzolanic activities. The kinetics of the SF–lime and DK–lime reactions were investigated in pastes at room temperature, 100°C, and 180°C by the determination of unreacted lime and combined water. The hydration products were identified by X-ray diffraction (XRD). The variations in mechanical properties were correlated with the reaction kinetics and the hydration products formed. DK exhibited higher reactivity than SF at all temperatures studied. Tobermorite was formed at 100°C in the high-lime DK mix at 14 days and extensively formed by autoclaving at 180°C curing due to the presence of Al and sulfate in the DK. The very low C/S ratios of SF mixes and low-lime DK mix prevent tobermorite formation and promote the formation of poorly crystalline C-S-H with a higher surface area.