Pozzolanicity of the material obtained in the simultaneous calcination of biomass and kaolinitic clay

• Kaolinitic clay was thermally treated in presence of rice husk.
• Calorimetry, X Ray Diffraction and thermogravimetric measures on blended cement pastes were performed.
• Compressive strength was determined on blended cement mortars.
• Pozzolanic activity of metakaolin obtained by calcinations in presence of rice husk was evaluated.

The scope of this paper is to study the pozzolanic activity of metakaolin obtained in simultaneous calcinations with rice husk. Isolated calcinations of kaolinitic clay and rice husk were also performed for comparison. The raw materials were subjected to thermal treatments in a gas furnace at 670, 700 and 750 °C for 2.0, 2.5 and 3.0 h. Based on the loss of crystallinity of the materials obtained, two of them were selected and ground in a ceramic ball mill to prepare pastes with ordinary Portland cement (OPC) with levels of substitution of 10% and 20%, with a water/binder ratio of 0.4 and mortars with a water/binder ratio of 0.5 in order to evaluate the pozzolanic activity of the materials by X Ray Diffraction analysis, isothermal calorimetry, thermogravimetric analysis and compressive strength measurements. The curing ages were 1, 3, 7 and 28 days at normal curing conditions. Based on the results it was concluded that, the cement mixed with the supplementary cementitious materials (SCMs) obtained in simultaneous calcinations, present a slow pozzolanic activity with an improvement in compressive strength of up to 20.1% in relation to the OPC and of 5.5%, at 28 days of normal curing, in relation to the highest value found for the cement substituted with materials obtained in isolated calcinations. In general, good linear correlations were found between compressive strength values in mortars and fixed lime in cement pastes suggesting a strong dependence of compressive strength on the amount of fixed lime by the pozzolans.