Addition of low reactive clay into metakaolin-based geopolymer formulation: Synthesis, existence domains and properties

• Low reactive Tunisian clay was added into metakaolin-based geopolymer.
• Consolidated materials existing domains were determined.
• The associated minerals reinforce the geopolymer material.
• The polycondensation rate depends on the amount of reactive aluminosilicate species.
• The mechanical properties depend on the extent of depolymerization of the solution.

This paper investigates the addition of low reactive Tunisian clay into metakaolin-based geopolymer as a valorization way in alkaline media. To conduct this investigation, the aluminosilicate precursors used were primarily characterized. Then, several samples were prepared by varying the amounts of metakaolin and clay in the mixture as well as the Si/K molar ratio of the alkaline solution. Correlations between (i) the polycondensation rate of the synthesized mixtures, followed by FTIR spectroscopy; (ii) the working properties, evaluated by the compression test; and (iii) the chemical composition were established, and a model of reactivity was proposed to elucidate the different networks formed for each sample. It appears that the Tunisian clay, after heat treatment, exhibits some reactivity that allows for the formation of consolidated materials. The associated minerals present in the clay seem not to participate in the polycondensation reaction and are simply agglomerated by the alkaline solution. However, the increase of the proportion of metakaolin in the mixture and the depolymerized species in the alkaline solution may improve the polycondensation rate and the working properties of the final materials. The optimal properties were obtained for a mixture of 50% low reactive Tunisian clay and 50% metakaolin and a Si/K ratio of the alkaline solution of 0.50.

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