Calcined clays present an economically and ecologically interesting perspective as supplementary cementitious materials with a high potential for technological optimization of blended binders. In order to describe the complex reactions of calcined natural occurring mixed clays, it is necessary to understand the influence of the individual components with different alumina/silica ratio in their chemical composition. The study investigates the reaction kinetics of three components of natural mixed calcined clays: metakaolin, illite (contains 10% by mass kaolinite and 12% by mass calcite) and muscovite at their optimized calcination temperatures. An artificial alkaline pore solution was adapted for leaching of the calcined clays. Two test series were performed with and without sulfate being present. The composition of the calcined clay-portlandite (CH)-alkaline solution pastes were prepared with a ratio 1:1:2. The hydration kinetics were determined by means of isothermal calorimetry and quantitative x-ray-diffraction for 48 hours (in-situ) and at 7, 14, and 28 days by means of the external standard G-factor method and additionally for not or less crystalline phases using the PONKCS method. Peaks-phase or hkl-phase models were used to account for the kapton-film and to quantify the free water, the C-S-H phase and the calcined clay. Thermal analysis is used to review the results of the XRD quantification. Further investigations revealed an improved alumina and silicon ion solubility with increasing alkali content. While metakaolin exhibits a significant concentration of dissolved alumina and silicon ions after six hours, the influences of illite and muscovite are less pronounced and start at later times of hydration. The formation of C-S-H and in presence of sulfate and calcite the formation of AFm- and AFt-phases can be quantified. C-A-S-H and strätlingite are formed in alumina rich clay compositions. In conclusion the investigation shows the quantitative contribution to the pozzolanic reaction in model pore solutions of different calcined clay components.    «

Calcined clays present an economically and ecologically interesting perspective as supplementary cementitious materials with a high potential for technological optimization of blended binders. In order to describe the complex reactions of calcined natural occurring mixed clays, it is necessary to understand the influence of the individual components with different alumina/silica ratio in their chemical composition. The study investigates the reaction kinetics of three components of natural mix...    »