Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization

Significance 

Building infrastructure for space exploration and habitation pose tremendous engineering challenges. Characterized by extreme temperatures in the lunar environmental cycles at the poles (the proposed landing for Project Artemis), the vacuum of space, and very limited access to water, most conventional construction materials, such as ordinary Portland cement (OPC, are not suitable as construction materials under space conditions. Not only does OPC require a significant amount of water, it is prohibitively costly to transport from Earth to the Moon or Mars. These limitations present a significant challenge for traditional approaches to manufacturing construction materials, suggesting fundamentally new, innovative approaches are necessary

Space exploration, therefore requires in-situ resource utilization (ISRU) developing construction materials using Martian/Lunar regolith instead of terrestrial resources. Lunar regolith is the topsoil layer on the lunar surface and it consists of mainly anorthosite and basaltic rocks. Consequently, in addition to the lunar regolith samples returned by the Apollo astronauts, significant research by NASA and other nations study regolith properties using rover missions as well as instrumented satellites, resulting in simulant soils consisting of terrestrial volcanic ash and other natural minerals that mimic the geochemistry and morphology of a variety of lunar and Martian regoliths for earth-based research.

Several strategies have been proposed for extra-terrestrial construction, including solar-sintered regolith and sorel cement. Extra-terrestrial cement is mainly required for developing vertical takeoff/landing pads for Martian and lunar surfaces to protect against secondary ejecta consisting of debris and dust kicked up by landings and take-offs, as well as habitats to protect humans and equipment against the harsh environmental conditions, including radiation. Compared with other strategies, the geopolymer binder has several advantages. It can serve as a bulk binder because it is rich in aluminosilicate minerals, and it requires less energy and water to prepare. Interestingly, the feasibility of producing geopolymer binders using Martian and lunar regolith simulants has been demonstrated. However, more studies are still needed to understand geopolymer binders fabricated from different regolith simulants and methods.

In their research efforts to provide cutting-edge technology that will support such long-term exploration and inhabitation of space, Dr. Jennifer Mills, Dr. Maria Katzarova and Professor Norman Wagner from the University of Delaware created a framework for comparing lunar and Martian regolith simulant-based geopolymer binders fabricated via alkali activation for ISRU. The authors also studied the environmental exposure effects (sub-freezing temperatures, vacuum and high temperatures) on the strength of the binder cement. They commenced by formulating geopolymer binders using lunar and Martian regolith simulants. Finally, they measured the material properties and characterized the microstructural evolution of the geopolymer binders under different environmental conditions. Their work is currently published in the journal, Advances in Space Research.

The researchers reported the successful conversion of one Martian regolith simulant and three lunar regolith simulants to geopolymer binders via alkali activation with sodium silicate. They recommended decreasing the solid content and increasing amorphous aluminosilicate content for effective activation of Martian simulant because small particles and aluminosilicate enhance the comprehensive strength of the binders under ambient curing. The comprehensive strength of all the three lunar simulant binders was decreased in vacuum and low-temperature conditions but increased in high temperatures (600 °C). A reduction in the comprehensive strength of Martian binders after heating was attributed to the high content of magnesium and iron.

Overall, variability in minerology, morphology and chemical composition of the regolith simulants exhibited different impacts on the mechanical properties of the final binders. The comparison of the strength properties of the binders with those in literature also emphasized the effects of these parameters on the comprehensive strength despite the differences in formulation and processing procedures. Furthermore, it was noted that extreme conditions could enhance the effects of chemical differences on reaction time and binder conversion due to the close link between reaction kinetics and chemical compositions.

In summary, the authors explored the application of lunar and Martian regoliths to fabricate high-performance construction materials suitable for use as landing pad structures for rockets. The findings support the need to further develop geopolymer binders for ISRU construction. It also provided a framework for understanding the possible differences between regolith simulants across literature research and under different environmental exposures. In a statement to Advances in Engineering, the team explained that the findings of their study will enable the development of a landing pad within the current payload limitations by sending activators to the lunar surface. Prof. Wagner’s research group includes significant efforts to develop geopolymers for earth-based sustainable construction materials, showing the dual use of this advanced space technology development to improve the human condition here on Earth.

Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization - Advances in Engineering

About the author

Norman J. Wagner is an Alison Professor of the University of Delaware and holds the distinguished Unidel Robert L. Pigford Chair in Chemical Engineering, with affiliated faculty appointments in Physics and Astronomy, Biomechanics and Movement Science, and Biomedical Engineering. He leads an interdisciplinary research team at the University of Delaware. He was President of the Society of Rheology (American Institute of Physics Member Society), is the co-founder and director of the Center for Neutron Science www.cns.che.udel.edu, and served as Chair of the CBE Department from 2007-2012. He was elected to the National Academy of Inventors in 2016 and the National Academy of Engineering in 2015, and is a fellow of both the AAAS and NSSA. He leads an active research group with focus on the rheology of complex fluids, neutron scattering, colloid and polymer science, applied statistical mechanics, nanotechnology and particle technology. He is also the PI on a mid-range infrastructure project funded by the National Science Foundation to build a world-class neutron spin echo instrument at the NIST Center for Neutron Research. Prof. Wagner co-founded STF Technologies LLC in 2003 to commercialize his inventions for applications in personal protective equipment and astronaut protection for NASA, as well as new scientific instruments. More about Professor Wagner, including his three textbooks, many patents and research publications can be found at www.cbe.udel.edu/wagner.

About the author

Jennifer N. Mills is a recent PhD graduate from the Chemical and Biomolecular Engineering Department at the University of Delaware. Her PhD research focused on the chemistry and structure-property relationships of sustainable alternatives to traditional cements, including geopolymers and other alkali-actiavted materials. She has also been involved with the Society of Rheology, serving as the first ever Student Representative to the Executive Committee from 2020-2022. She is currently employed by the Dow Chemical Company in Collegeville, PA.

About the author

Maria Katzarova is a polymer rheologist in the Lubrizol Advanced Materials segment for engineered materials. She holds a doctoral degree in chemical engineering from the Illinois Institute of Technology where she modeled the bulk rheolgical response of dense polymeric systems to deformation. Prior to joining Lubrizol, she leveraged her expertise in theoretical and experimental rheology of rate-responsive materials at the University of Delaware in collaboration with NASA for the design and characterization of mechanically resilient spacesuit materials and in situ regolith utilization for extraterrestrial construction.

Reference

Mills, J., Katzarova, M., & Wagner, N. (2022). Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilizationAdvances In Space Research, 69(1), 761-777.

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