Investigation of severe lunar environmental conditions on the physical and mechanical properties of lunar regolith geopolymers

3D-printing of geopolymers produced from lunar regolith is an interesting option for space in situ habitats. In this study, the influence of the severe lunar environmental conditions such as extreme temperature variations and vacuum on the physical and mechanical properties of lunar regolith geopolymers were investigated. Additionally, the effect of different amounts of urea as a geopolymer superplasticizer was evaluated. Utilization of urea was found to reduce the water needed to reach the same workability by up to 32%. Extrudability tests showed that mixtures containing 3 wt.% urea could be continuously extruded, and built up into a five layer structure without any noticeable deformation. Addition of urea decreased the compressive strength after exposure to the temperature variations of one lunar dayeandenight cycle during curing. However, urea can prevent concrete degradation after the lunar cycle by increasing the amounts of air voids. X-ray tomography showed that the porosity became higher when urea was added to the samples, and increased markedly when the samples were cured in vacuum.