Effect of mixing metakaolins: Methodological approach to estimate metakaolin reactivity

Geopolymers are obtained from an alkali silicate solution and aluminosilicate sources. The source commonly used geopolymer is metakaolin. The chemical composition, extraction site or calcination process of metakaolin influence its reactivity and thus the properties of the consolidated samples. This work focused on clarifying how the properties of aluminosilicate-based raw materials evolve when different metakaolin sources are mixed. The study involved mixing different metakaolins to evaluate their physico-chemical properties. The different samples were characterized by measuring their granulometry, wettability and zeta potential. Structural data were obtained from X-ray diffraction and 27Al nuclear magnetic resonance spectroscopy. It appears that the properties of the mixtures can be expressed as a function of different parameters. Granulometric properties directly depend on the quantity of each source, wettability is related to the amount of available amorphous aluminum in the sources, and zeta potential is strongly influenced by the source with the highest amount of siliceous-based impurities. This methodological approach can be applied to geopolymer synthesis.