Determining the structuration of biopolymer-bound soil composite

Engineers and scientists are in search of new construction materials to advance exploration in space and to reduce our CO2 emissions on Earth. Biopolymer-bound Soil Composite (BSC), a promising novel construction material, is being investigated for extrusion-based 3D printing applications that could both assist in lunar habitat construction and reduce earth-based CO2 emissions. For extrusion-based 3D printing applications, knowledge of BSC structuration is required. In this study, we evaluated the formation of a crust on the outer surface of BSC test specimens at various desiccation levels and the effect of the crust on the strength of the specimens. We measured the crust depth, determined the crust moisture content, and performed uniaxial compressive strength testing for selected specimens. We found that the depth of the BSC crust develops linearly with overall desiccation level and is the source of the specimen’s initial strength and stiffness. Additionally, we found that the crust begins to form when the biopolymer solution concentration at the specimen surface reaches a critical value and then moves inward with moisture loss. A methodology for modeling BSC structuration is developed based on knowledge of the BSC mixture design, the level of BSC desiccation, and the crust-forming biopolymer solution concentration.