Mineralogical characteristics influence the structure and pozzolanic reactivity of thermally and mechano-chemically activated meta-kaolinites

Increasing early age reactivity of cement replacements is a barrier to reducing the embodied carbon of blended Portland cements. Mechano-chemical activation is an emerging alternative to conventional thermal activation for clays, which can accelerate early age reactivity. Knowledge gaps on the structure and reactivity of mechano-chemically activated kaolinitic clays include the influence of Fe-bearing phases and the mineralogical characteristics of kaolinites from different sources. This study evaluated the effectiveness of mechano-chemical vs. thermal activation for an Fe-rich clay containing disordered kaolinite and 24 wt% goethite, and a low-Fe clay containing highly ordered kaolinite. In the Fe-rich clay, mechano-chemical activation simultaneously caused dehydroxylation of kaolinite to form meta-kaolinite, and dehydration of goethite to form hematite. Agglomerates of intermixed meta-kaolinite and goethite/hematite nanoparticles were shown to have similar Al and Si environments after thermal or mechano-chemical activation (as determined by STEM-EDX, 27 Al and 29 Si MAS nuclear magnetic resonance and electron energy loss spectroscopy). Mechano-chemical activation enhanced early age (