Effect of reactivity of different metakaolin mixtures on geopolymer extrudability

Abstract

Additive manufacturing of geopolymers is an innovative technology for research and development This work highlights effect of different metakaolin of mixtures reactivity on geopolymer extrudability. Extrudability tests were carried out on geopolymer pastes from different metakaolin ternaries diagrams using two alkaline (potassium silicates K and sodium silicate KNa) solutions. Extrudable areas were delimited. To understand the differences, the reactivity of the different metakaolin mixtures was evaluated. The results showed that for the extrudable areas, the zeta potential values of the metakaolin mixtures ranged from −50 to −60 mV with K solution and were around −60 mV with the change of solution (KNa). Moreover, the extrudable area corresponds to an energy of oligomer formation (determined by thermal analysis) determined between 1.67 and 1.85 kJ mol−1 with metakaolin ternary diagram M1-MI-M5 and 1.58 and 1.76 kJ mol−1 for metakaolin ternary diagram M1-M2-M5. Whatever the alkaline solution used, the alkaline cation concentration of the extrudable domains is greater than or equal to 2.80 mol. L−1. Mechanical strengths increase around 10 % from solution K to KNa. All these results are confirmed by using other aluminosilicate sources, such as argillite (clay calcined at 650 °C) and mixture of several clays (A65030-M170 and A65050-M150).