Ceramics-Silikáty 64, (2) 145 - 154 (2020)

This study estimates the influence of the different pozzolanic activity micro-fillers on the hydration of Portland cement. Cements with binary blends of ordinary Portland cement and different micro-fillers (15% by mass) were developed and their characteristics were investigated in terms of the fineness, chemical composition, mineral composition, setting time, particle distribution, hydration heat, water demand, changes in the mineral composition during the hydration, and the compressive strength. All the specific properties of the blended cement pastes were compared with the pure Portland cement paste. The study showed that the investigated micro-fillers (except for quartz sand) increase the initial hydration of the Portland cement. In addition to this, the inert limestone micro-filler mainly affects the initial hydration of the calcium silicates, whereas the pozzolanic active micro-fillers (calcined mica and kaolinitic clay and its mixture) affect both processes: the initial hydration of the calcium silicates and the reaction of the aluminate-bearing phase with the gypsum. The inert micro-fillers (especially limestone) are more effective at the early stage of hardening (up to 7 days), but later, after 28 days, the compressive strength of the samples directly depends on the activity of the micro-fillers. All investigated pozzolanic active micro-fillers promote the formation of the calcium silicate hydrates, however, only in the samples with the most active (kaolinitic clay) micro-filler after 28 days of hardening clearly identifies the pozzolanic reaction. In contrast to the active micro-fillers, the inert micro-fillers increase the amount of portlandite in the hardened cement paste.