Development of supplementary cementitious materials from Algerian kaolin: elaboration of metakaolin and assessment of pozzolanicity

Researches on the use of metakaolin, as a supplementary cementitious material (SCM), are growing worldwide due to its environmental and technical benefits. Metakaolin is usually obtained by calcining kaolinitic clay; however, the thermal cycle of calcination should ensure the optimal kaolin to Metakaolin conversion. This experimental investigation aims to examine the effect of calcination parameters on two Algerian kaolins (KT1 and KT2), used to elaborate Metakaolins. The raw ground materials have undergone various thermal cycles, by varying the target temperature (from 500 to 1000 °C) and the holding time (2, 3 and 5 h). The optimal thermal cycle was checked by assessing the pozzolanic reactivity using mechanical, physical and chemical methods. Results of the various tests were in perfect agreement, and they show that the calcination enhanced pozzolanic reactivity and that the thermal cycle of 800 °C–5 h allowed obtaining the highest pozzolanicity. The treatment of KT1 led to a compressive strength slightly better than that of the control mortar and a lime consumption of 767 mg/g. However, results of the treated KT2 were more important, it recorded an improvement of about 6% in compressive strength and a lime consumption of 843 mg/g. It has been concluded, therefore, that both materials have significant pozzolanic potential and deserve to be valued as SCMs and used in environmentally friendly cement.