Influence of calcination temperature in the pozzolanic reactivity of a low grade kaolinitic clay

The influence of thermal activation temperature in the pozzolanic reactivity of low grade kaolinitic clay is assessed in this paper. The raw material, with approximately 40% kaolinite and 40% of 2:1 clay minerals, was calcined to temperatures ranging between 500-1000 °C. Mortars with a 30% replacement of OPC by the clay calcined at 800 °C, a temperature representing the best compromise between structural disorder of the clay fraction and its specific surface, show values of compressive strength from seven days on similar or higher than the reference 100% OPC mortars. Pozzolanic reactivity assessed by cumulative heat of lime-pozzolan pastes are in correspondence with these results. The increase in compressive strength with calcination temperature up to 800 °C could be associated to a more complete thermal activation of the multicomponent clay fraction. The experimental results indicate that low grade kaolinitic clay deposits with moderate contents of kaolinite constitute a potential source of high reactivity pozzolanic materials.