Influence of Calcining Temperature on the Mineralogical and Mechanical Performance of Calcined Impure Kaolinitic Clays in Portland Cement Mortars

In this work, the effects of calcination temperatures ranging from 600°C to 1,000°C on the changes in mineralogical phases and mechanical characteristics of calcined impure kaolinite clay blended cement mortars were investigated. The impact of calcining temperature on pozzolanic activity of impure kaolinite clay was evaluated using direct and indirect methods. The findings demonstrated that at 700°C, kaolinite changed from a crystalline to an amorphous metakaolin phase. Specific surface, water demand, and setting time of the blended cements decreased as calcining temperature increased. The compressive strengths of blended cement mortar containing low-grade clay calcined at 700°C, 800°C, and 900°C were found to be greater than that of 600°C and 1,000°C. Based on the results of pozzolanic reactivity evaluations and compressive strength development, the most effective calcining temperature was shown to be between 800°C and 900°C.