Mechanical activation of metakaolin through milling: Impact on the geopolymerization process

There is a limited understanding of the mechanical activation mechanisms that enhance the geopolymerization reactivity of aluminosilicate materials. For this purpose, this paper systematically investigates the microstructures of metakaolin with varying reactivities, along with the geopolymers prepared from them. The findings indicate that the mechanical activation mechanism of metakaolin encompasses several processes: a reduction in particle size, an increase in specific surface area, the transformation of multilayer lamellar stacked structures into monolayer lamellar structures, the amorphization of potassium mica crystals, the dissociation of the aluminosilicate network structure on the particle surface, and the enrichment of Al at the particle surface. In comparison to geopolymers prepared with untreated metakaolin, those made with metakaolin mechanically activated for 4 h exhibited a 28.7 % increase in compressive strength after a setting time of 7 days, and a 53.0 % increase in early compressive strength after a setting time of 8 h.