Role of amorphous phase, temperature fluctuations, and vacuum, on the performance of alkali-activated lunar regolith simulants

This study explores the feasibility of using alkali-activated regolith for construction in lunar environment. The composition of the reactive glassy fraction present in lunar regolith simulant is assessed in detail, with the aim of tailoring suitable alkaline activators that can maximise the reactivity of the system without leading to the release of excess alkali in solution or formation of unwanted products such as amorphous silica. The obtained results suggest that the low amount of reactive aluminium present in the regolith can be compensated by either the addition of moderate amounts (< 10 wt%) of metakaolin or the use of a sodium aluminate activator. After ascertaining an adequate mechanical performance in standard terrestrial conditions, we assessed the role of vacuum on the fresh properties, and of combined vacuum and extreme temperature variations (− 50 °C to + 100 °C) on the hardened properties. It was observed that, while the exposure to vacuum and temperature fluctuations after setting did not significantly affect strength and microstructural development, exposure to vacuum when the samples are still in the fresh state leads to significant formation of macropores due to solvent evaporation. This process, however, did not inhibit setting and hardening. Finally, feasibility in a real lunar environment, limitations and future directions are discussed.