UC San Diego

Sustainable habitat construction on the Moon and Mars focuses on in situ resource utilization (ISRU) to produce infrastructural materials while minimizing recurring supplies from Earth. The current study first explores uniaxial compaction of the soil simulants JSC-1A and JSC Mars-1a with binders. Solvents, monomer polymerization, and melt-compression are investigated for mixing binders with simulants. Results and challenges pertaining to each method are discussed. The second and main part of the current study investigates uniaxial compaction of Mars-1a and montmorillonite without binders. Experimental parameters include initial particle size, compression pressure, lateral boundary condition, and rate of loading. Mechanical strength of compacts is determined via three-point bending flexural strength. The applied compression pressure and lateral boundary condition strongly influence resultant strengths, while initial particle size and rate of loading exhibit more subtle effects. High compression pressures with reduced lateral boundaries generate ~30MPa flexural strength, stronger than a typical steel-reinforced concrete. A smaller initial particle size achieves higher strength. Impact loading of Mars-1a samples achieves marginally higher flexural strength compared to a given peak pressure in the quasi-static case, while montmorillonite shows no such difference. For the former, enhanced particle motion and phase transformation during impact may account for the higher strength. A given impact energy leads to similar flexural strengths regardless of variations in hammer mass or velocity. Characterization using thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, CHNS/O elemental analysis, and evolved gas analysis corroborates the notion that a high specific surface develops secondary bonding responsible for strength. Characterization also rules out possible roles for trace water or organic matter on compaction strengthening. Compaction of analogue materials points toward nanoparticulate iron oxides as the agent of strengthening in Mars-1a. Measured nitrogen permeability suggests the solids are akin to dense rocks. Volumetric energy efficiency is estimated at 0.3-0.4GJ/m3, or about one order of magnitude lower than thermal processes. The compaction process is expected to be scalable and portable to extant or emergent prototyping technologies.