Thermal activation of kaolinite through potassium acetate intercalation: A structural and reactivity study

Abstract

Calcined clays have emerged as a suitable alternative to partially replace conventional cement due to their highpozzolanic activity. This study explores a novel activation methodology for kaolinite, aiming to obtain metakaolinat lower temperatures than conventional thermal activation. This methodology involves a prior intercalationstage with potassium acetate (KAc) before thermal activation. The effectiveness of KAc intercalation wasassessed through X-ray diffraction (XRD), indicating an intercalation ratio of approximately 90%. Severalcalcined temperatures were tested in accordance with the thermal behaviour analyzed through thermogravimetricanalysis (TGA). Once calcined, the intercalated kaolinites exhibited enhanced reactivity compared toconventional calcined clays in the range between 400 ◦C to 550 ◦C, as demonstrated by modified Chapelle andSi/Al availability tests. A comprehensive structural characterization was conducted to facilitate a better understandingof the novel KAc-based metakaolin reactivity through various techniques (XRD, 27Al - 1H MAS NMR,and TGA). This focused on the crystalline changes in the kaolinite structure, the evolution of Al atoms conformation,and the OH behaviour at different thermal activation temperatures. Overall, this study highlights thepotential of KAc intercalation as a strategy to obtain higher metakaolin content at lower temperatures thanthrough conventional thermal treatments, offering insights into the development of its potential use as supplementarycementitious materials or alternative cementitious materials precursor.