Development of geopolymeric inks for direct ink writing based on lunar regolith simulants

In recent years, renewed interest in Lunar exploration has motivated research into strategies to achieve a permanent human presence on the Moon. In-Situ Resource Utilization (ISRU) approaches have been widely recognized as a promising option to mitigate the high costs associated with the transport of construction material from Earth to build long-term structures on the Moon. In particular, Lunar regolith is mostly composed of aluminosilicate minerals with a substantial amorphous fraction which can be converted into a geopolymer by alkali activation, providing materials suitable for construction applications. Thus, this project aims to develop and optimize geopolymer slurries for in-situ Additive Manufacturing in a Lunar environment, utilizing a regolith simulant that closely replicates the composition and properties of real soil found on the Moon. The optimization of slurry formulation for 3D Printing, using the Direct Ink Writing (DIW) method, primarily focused on the selection and incorporation of suitable additives to enhance printability. This aspect is part of the larger GLAMS project (Geopolymers for Lunar Additive Manufacturing and Sensing), funded and supervised by the Italian Space Agency (ASI), aiming to develop technologies and strategies for large-scale Lunar construction using regolith-derived geopolymeric materials. Two additives were tested: cellulose and bentonite clay. The use of cellulose was unsuccessful, and formulation of a printable slurry was not achieved despite several attempts. In contrast, three successful compositions were optimized using bentonite clay as a additive, displaying good printability and excellent mechanical properties after consolidation: despite the need to transport this type of additive from Earth, printable formulations were achieved in all cases using mass fractions lower than 5%. Once a reliable slurry formulation was achieved, the curing of the samples was tested under “Lunar” conditions, which involved exposing them to cold and hot temperatures that simulate the extreme temperature fluctuations on the Moon. Various characterization methods were used to gain better insight into the specific properties of the materials, including porosity measurements, mechanical tests, and microscopy. These characterizations provide valuable insights into the feasibility of such materials and whether they would be able to withstand the harsh conditions of the Lunar environment.