Lunar regolith simulant-based geopolymer products prepared by the cold-sintering process: Evolution of pore water distribution, reaction products, microstructure and performance

This study proposes a cold sintering process (CSP) for fabricating lunar regolith simulant-based geopolymer products, addressing the constraints of limited energy resources and launch payload efficiency on the lunar surface. The investigation systematically examines how controlled variations in water addition (3–11 wt%) and alkali content (0.01–0.04) influence pore water distribution, reaction products, microstructural evolution, and macroscopic properties of the geopolymer. Through optimization of the sintering liquid phase composition, the compressive strength was enhanced from 54.56 MPa to 205.87 MPa while achieving a density increase from 2.23 g/cm³ to 2.54 g/cm³ . LF NMR analysis coupled with thermogravimetric measurements confirms the progressive conversion of capillary water into gel-bound nanopore water, while both alkali content and water addition demonstrate significant correlations with CSP process efficiency. Increasing the alkali content from 0.01 to 0.04 resulted in a notable enhancement of gel water content from 0.616 wt% to 1.404 wt%, accompanied by a 26.7 % reduction in total porosity (0.056 → 0.041 ml/g). The densification process is primarily governed by pressure-solution creep mechanisms, wherein preferential dissolution at high-stress particle contacts facilitates solute diffusion through the liquid phase followed by reprecipitation in low-stress regions, enabling the preparation of high-performance geopolymer blocks within 60 minutes. The CSP achieves a 70–90 % reduction in water consumption compared to conventional casting methods (30–45 wt%) while completely eliminating the multi-day curing requirements (3–28 days) typically associated with mold-casting processes. This study establishes an energy-efficient rapid manufacturing strategy for high-performance lunar construction materials that satisfies the critical requirements for extreme environmental adaptability.