Research paperThe influence of alkali activator type, curing temperature and gibbsite on the geopolymerization of an interstratified illite-smectite rich clay from Friedland

- Geopolymers are formed by alkaline activation of an interstratified illite-smectite clay.
- KOH-activation at 50 °C forms geopolymers with compressive strength of 38 to 45 N/mm2.
- Gibbsite addition enhances KOH-activation by increased aluminosilicate gel formation.
- NaOH-activation at 75 °C forms geopolymers with lower strength of ~ 30 N/mm2.
- NaOH-activation is characterized by phillipsite (zeolite) crystallization.

Illitic clays, such as the interstratified illite-smectite clays, are one of the most abundant aluminosilicates on Earth's surface and are widely available for geopolymer production. Geopolymers are a group of alkali-activated materials, which are gaining increasing attention as low-CO2 binders with some advantageous properties compared to ordinary Portland cement. In this study, high strength geopolymers were formed from a calcined and ground interstratified illite-smectite clay, which was mixed with 6 M NaOH or KOH and cured at 25, 50 and 75 °C. We furthermore tested the effect of increasing Al content of the precursor by adding gibbsite to the metaclay. The temperature dependent reactivity of the precursor, i.e. the Si and Al solubility of the metaclay and gibbsite is shown. It is revealed that the geopolymerization of the meta-illite-smectite clay was favored by KOH-activation at 50 °C. Adding 10 wt% gibbsite by solid mass increased the strength of the geopolymers by ~ 20% from 38 to 45 N/mm2, which is partly attributed to increased formation of an amorphous aluminosilicate gel. NaOH-activation was not affected by gibbsite addition and increased strength only at 75 °C, which was related to phillipsite (zeolite) crystallization. Na-geopolymers showed lower strength of ~ 30 N/mm2 and abundant capillary pores.