Optimized Mix Design and 3D Printing Application of Magnesium Oxysulfate-Based Martian Concrete Using 100% In-Situ Resources (2026-02)¶

3D printing construction technology is one of the core technical approaches for habitat construction in the extreme environment of Mars. However, existing 3D printing-based Martian concrete technical schemes still face key technical challenges, such as significant difficulties in acquiring in-situ building materials, complex preparation processes, lack of suitable setting properties, and insufficient mechanical performance. This study develops and optimizes a magnesium-oxysulfate-based Martian concrete formulated entirely from in-situ resources (ISRU). The effects of the α-MgO/MgSO₄ molar ratio, water-to-material ratio, and phosphoric acid content on setting characteristics and mechanical performance were systematically investigated. Through XRD and SEM analyses combined with 3D printing trials, an optimal mix design was identified. The results show that the material achieves superior overall performance at an α-MgO/MgSO₄ molar ratio of 8:1, a water-to-material ratio of 0.19, and zero phosphoric acid content. The initial setting time stabilizes at approximately 5 min, suitable for rapid construction under extreme environments. The 3-day and 28-day compressive strengths reach 15.34 MPa and 22.13 MPa, respectively, with the early-age strength reaching nearly 70% of the long-term strength. Microstructural observations reveal petal-like Mg(OH)₂ as the primary hydration product, while the inert regolith analog particles retain their original phases and contribute to matrix densification. 3D printing tests demonstrated continuous material extrusion without clogging or collapse. The printed components exhibited an overall deviation of 2.4% in diameter and height, and a wall thickness deviation of 2.6%, which meets the construction precision requirements. This study provides key technical support for ISRU-based 3D printing construction on Mars.