Ceramics-Silikáty 50 (1) 15-21 (2006)

The effect of pozzolana on the properties of the finest fraction of separated Portland cement - Part 1

R. Kaminskas, J. Mituzas, A. Kaminskas

This study deals with compressive strength of the fine Portland cement fraction being collected in the sleeve filters during clinker milling. This fraction has much higher amount of gypsum (12.1 wt. %) and specific surface area 1340 m²/kg, when comparing it with ordinary Portland cement (OPC). The compressive strength of the fine fraction after 24 hours of hydration is three times higher than that of OPC. This tendency persists also after 7 days. However, after 28 days of hardening, the compressive strength of the fine fraction decreases down to 27 MPa being 1.5 times lower than that of OPC (43 MPa). This decrease is affected by high growth rate of ettringite crystal, which is initiated by elevated content of gypsum. Carbonated pozzolana additive does not change the course of hydration process. The compressive strength of the fine fraction samples with pozzolana additive is after 28 and 180 days of hardening two times lower than that of OPC samples.

Keywords: Finest cement fraction, Carbonated pozzolana, Ettringite