A review of lunar regolith based alkali activated materials and sintered regolith for use as a construction material

Over the last decade there have been numerous studies that propose regolith-based materials, such as regolith based geopolymers and sintered blocks, for permanent manned missions on the lunar surface, like those proposed by space agencies like the National Aeronautics and Space Administration in the US. In this review paper the current state of research was investigated for both of the materials described above, providing an overview of the methods of manufacture for their deployment as well as the mix designs used to meet the harsh environmental conditions of the lunar surface. For regolith based geopolymers, the primary methods of deposition are cast parts and large-scale 3D extrusion printing. For this application researchers have been focused on finding the relationship between water content, extreme temperature curing, and vacuum curing on the final mechanical performance and morphology. Because of the wide range of activation solutions and regolith simulants available to researchers, the main concern has been placed on optimizing the process methods for deposition and simulant chemistry. A similar situation is seen in regolith sintering where the heating method, configuration, and pretreatment limit the shape of the parts and the final properties. These sintered blocks were shown to have a high compressive strength but are limited by the part size and have high variability in performance due to inconsistent powder compositions. Based on our review, the research discussed in this paper on the curing conditions, testing, and manufacturing methods for lunar construction materials, a research gap was seen in providing large scale mechanical and degradation datasets on these materials for construction applications. This gap was also paired with a lack of standardization in regolith simulants and curing methods that accurately predict the conditions expected by lunar mission planners.