Composition-property relationships of BP-1 lunar regolith simulant geopolymers for in-situ resource utilization

Abstract

In-situ resource utilization (ISRU) to construct environmental protection and critical infrastructure is required for long-term human habitation on the Moon and Mars. Analogous to terrestrial construction materials formed from aluminosilicates, i.e., geopolymers, construction materials formed from lunar aluminosilicate regolith are a promising method to create lunar landing pads and habitats. Building on a previous lateral study across multiple regolith simulants, the effects of composition on one specific regolith simulant, Black Point 1 (BP-1), are investigated with the goal of developing relationships between composition and properties. The effects of overall geopolymer composition, activating solution silica and sodium content, and activating solution water content on seven-day compressive strength, strain to fail, and secant modulus are investigated. Decreasing water content has a positive effect on compressive strength and secant modulus of geopolymers formed at ambient-earth conditions, reaching maximum compressive strength at 75 wt% BP-1. Above a compositional limit of Si/H2O = 0.6, differences in Si and Al coordination result in variations in compressive strength with the elemental composition of the geopolymer. At high solids in formulation, the observed trend in compressive strength is nonmonotonic with varying silicon and aluminum content, emphasizing the need for a mechanistic understanding of the relationship between composition and structure for optimization of geopolymer material properties. This study provides a robust set of data for a widely available lunar regolith simulant that can guide further development of processing strategies for lunar ISRU.