Influence of low-pozzolanic activity calcined mica clay on hydration and hardening of Portland cement

Abstract

This study investigated the possibility of using artificial materials obtained during combustion of mica clay as an additive for Portland cement. The mica clay granules were burned at 700–1100°C for 1 h. It was considered that the pozzolanic activity of the investigated mica clay would depend on the combustion temperature. The highest pozzolanic activity (134 mg calcium oxide (CaO)/g) was observed in the samples calcined at a temperature of 900°C. In the samples, 5, 10, 15 and 25% (by weight) of the Portland cement was replaced with calcined additive at the temperature of 900°C. The samples were then hardened for 28 d under normal conditions. Owing to relatively low pozzolanic activity, the pozzolanic reaction in the samples with the additive up to 28 d of hydration was not noticeable. However, calcined mica clay additive acted as a microfiller and significantly increased the rate of hydration of Portland cement clinker minerals. The calcined mica clay additive had a positive effect on the compressive strength of samples cured for 28 d under normal conditions because up to 15 wt% of ordinary Portland cement can be replaced with the additive being investigated without impairing the strength class of the cement.