Improvement of the Pozzolanic Properties of Calcined Mica Clay

This study focused on the enhancement of the pozzolanic properties of thermally activated (calcined) mica clay (MC) by mixing it with smectite clay waste (SCW) from oil bleaching. Mica clay consists of small amounts of kaolinite, montmorillonite, illite, quartz, and carbonates, whereas smectite clay contains montmorillonite, an amorphous phase, and organic impurities. Samples were prepared by adding 10%, 30%, and 50% by weight SCW to the mica clay, followed by thermal activation at $600°\mathrm{C}–800°\mathrm{C}$ for 1 h, and finally milling after cooling. The obtained product was used as supplementary cementitious materials (SCMs). It was determined that the increase of calcination temperature and the amount of SCW additive improved the pozzolanic activity of the mixtures. The addition of 30% by weight SCW to the mixture calcined at 800°C increased the pozzolanic activity by 40%, whereas the addition of 50% by weight SCW increased the activity of the mixture by more than 1.5 times compared with that of the simple mica clay. The increase in the pozzolanic activity of the mixture was associated with the partial decomposition of the clay minerals throughout the combustion process and the presence of an amorphous phase from SCW. The obtained results show that combustion at 800°C of the mica clay mixture containing 30% SCW accelerated the early hydration of portland cement, and the samples containing the additive clearly exhibited signs of pozzolanic reaction after 28 days of hydration. The replacement of up to 15% by weight portland cement with the investigated additive increased the compressive strength of the samples.