Microstructural Analysis of the Reactivity Parameters of Calcined Clays

Abstract

Four (04) different types of clays from Burkina Faso were studied for their potential applications in the production of calcined clays as substitution materials for Portland cement. The study aimed at analyzing the factors affecting their reactivity. The untreated clays were subjected to various tests to highlight the intrinsic properties that can influence their reactivity. After the treatment by calcination, the clays were subjected to various pozzolanicity tests and microstructural analysis in order to evaluate their influence on the microstructure of the cement paste. The results showed that the reactivity of calcined clays is strongly related to the intrinsic properties of the raw clays, such as the content and the structure of kaolinite: disordered kaolinite reacts better than ordered kaolinite. After the calcination, the reactivity depends on the amorphous phase (amorphous content) of the clays, which influences the strength activity index. This study established a correlation between different parameters to easily identify the main properties of calcined clays that can influence their pozzolanic reactivity. All the results showed that the kaolinite content is a determining factor in the reactivity of clays before calcination. However, the study showed that the amorphous content of kaolinite is the determining parameter of the reactivity of calcined clays, as calcination can lead to the recrystallization of kaolinite.