Synthesizing lunar regolith-geopolymer emulating lunar positive temperature regime

The development of lunar habitat using lunar regolith is a captivating research area for constructing lunar bases, especially after the discovery of polar ice, and molecular water on the lunar south pole. The aim of this research is to synthesize a robust lunar regolith geopolymer by fine-tuning the concentration and ratios of alkaline activators while implementing curing under lunar positive thermal regime. The geopolymer was synthesized containing lunar highlands simulant (LHS-1) and mare regolith simulant (LMS-1) at the lowest water content using sodium (Na) and potassium (K) based alkaline activators emulating positive temperature regime collected by Diviner Lunar Radiometer Experiment (DLRE). The maximum compressive strength of 41.23 MPa was achieved for highlands regolith simulant-based geopolymer containing a Na-activator with the lowest water-to-precursor ratio of 0.23. The surplus alkali cations in the geopolymer paste matrix resulted in the formation of carbonation products after reacting with atmospheric carbon dioxide. K-activator geopolymer resulted in Kalicinite which has lower thermal stability and dissolution in water, whereas sodium carbonate formed in Na-activator-based geopolymer engrained and embedded precursor particles alongside sodium-calcium aluminosilicate hydrate (N-(C)-A-S-H) gel forming more densified microstructure. Conclusively, lunar regolith geopolymer has the potential for the construction of lunar habitat. However, this study recommends synthesizing geopolymer in vacuum conditions, emulating freeze-thaw cycles for a more precise estimation of microstructural developments and evaluating other critical properties.