Long-term Moon bases would represent a giant leap in space exploration. However, building permanent structures on the Moon would be astronomically expensive if made from terrestrial materials. A solution could consist in building a local concrete composed mainly or entirely of lunar soil (regolith). Previous ideas: Regolith can be melted, cast and cooled down to produce building blocks, or they can be pressed and sintered to the required shape. Instead, the use of heat or UV cured solvent-free polymers can be used to bind regolith (polymer concrete). The binding function of the polymers can be obtained also by triggering chemical reactions. The feasibility of using ordinary concrete as the main construction material on the Moon was demonstrated, but such a process requires a large amount of water and energy. More recently, the so-called geopolymerization process has been considered as an interesting alternative to ordinary cement. Through geopolymerization, lunar dust simulant was shown to produce rock-like material with higher mechanical strength than ordinary cements. New ideas: Producing foamed materials from regolith. The great advantage of foams is that only a small proportion of their final volume is needed to produce them from liquid matter, while their mechanical strength may be compatible with construction requirements, especially on the Moon, where the gravity force is divided by 6. Moreover, thermal insulation properties of foams are also to be considered as an advantage. In this project two strategies are proposed: (1) Solid geopolymer foam will be produced from the controlled foaming of regolith (simulant). (2) Thanks to specific bacteria colonies, biocementation will be induced in foamed suspension of regolith. The underlying mechanism is the precipitation of calcite by the bacteria in order to consolidate the packing of regolith particles embedded by bubbles in the precursor liquid foams.
