POZZOLANIC ACTIVITY OF MINERAL ADDITIVE BASED ON THERMOACTIVATED KAOLIN

The research is related to an important topical issue of studying the processes of kaolinite transformation into metakaolin during heating, which allow supplementing the existing provisions and patterns in terms of reducing the energy intensity of the thermal activation process and the pozzolanic activity of the resulting additive, on the other hand. The chemical composition of the original kaolin clay was determined. On the base of the results of laser diffraction, differential thermal and X-ray phase analysis, as well as infrared spectroscopy, the effect of kaolinite firing temperature on the granulometric composition, degree of dehydroxylation and amorphization of metakaolin was established. The authors determined the pozzolanic activity of the metakaolin mineral additive obtained by thermal activation of kaolin clay in the temperature range of 450-900 , when metakaolin was used as a partial replacement of Portland cement. The greatest increase in the compressive strength of the cement paste, both at the early and grade age is achieved by replacing part of the cement with a mineral additive - thermally activated kaolin at a temperature of 650. An increase in the water demand of the composite cement with the addition of the obtained metakaolin is noted. Higher values of the strength index of cement paste with the addition of metakaolin, obtained by heat treatment of kaolin clay at a temperature of 650 , are most likely explained by achieving the optimal temperature regime for firing kaolinite. In this case incomplete dehydroxylation, but the maximum degree of amorphization that determines the pozzolanic activity of the additive in terms of strength is achieved. The results obtained may be of interest for the practical implementation of the problem of reducing carbon dioxide emissions, resource and energy conservation, improving the construction and technical properties of materials obtained on the basis of a composite cement with the addition of metakaolin.