Metakaolin addition to improve geopolymerization process and properties of waste clay-based materials

The exploitation of different kind of clayey waste (halloysitic, smectitic/illitic, kaolinitic) for the production of geopolymers in the view of a circular economy of mines is the main goal of this study. In particular, the addition of low percentages of metakaolin (5-15%) was evaluated to improve the chemical-physical properties and the consolidation degree of geopolymeric formulations produced with clays classified as mine’s by-products. In fact, these secondary raw materials are often not sufficient alone to obtain chemically stable formulations with acceptable mechanical properties but require the addition of reactive fillers. All samples contained thermally treated clays (600°C-700°C) and metakaolin as aluminosilicate precursors, alkaline solution of NaOH and Na2SiO3, and were cured at room temperature. The influence on the final products with MK addition was monitored with the evaluation of the chemical stability in water (pH and ionic conductivity measures), the comparison of setting times (Vicat needle) and mechanical performance.