Solid Foams from Geopolymerization of Lunar Regolith Simulants Slurries

Robust, lightweight, and thermally insulating building materials, developed according to the In Situ Resource Utilization (ISRU) paradigm, are essential for enabling Moon settlements. With this aim, we have investigated the formulation and characterization of porous geopolymeric materials based on a lunar regolith simulant, focusing on the influence of surfactants and rheology-modifying additives on pore structure and final material performance. As an optimized procedure, a pre-formed TTAB foam was, in fact, incorporated into the geopolymeric precursor slurries to achieve a suitable porosity. Then, the effects of three thickeners (xanthan gum, bentonite, and Actigel-208) were evaluated in view of the possible utilization for the production of building blocks by 3D printing. Observations of the pore structure after the geopolymeric consolidation of the slurries showed predominantly closed-cell networks across all formulations, with a pore morphology strongly dependent on the thickener used. Xanthan gum promoted high porosity but reduced mechanical integrity, whereas bentonite produced denser structures with higher thermal conductivity. Actigel-208 provided the most balanced performance, combining adequate porosity with improved strength. These findings demonstrate the potential of producing thermally insulating, structurally stable solid foams from lunar regolith simulants via a geopolymerization route.