Towards Extraterrestrial Construction: Lunar Concrete for In-Situ Infrastructure on the Moon
Restricted (Penn State Only)
- Author:
- Collins, Peter
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 31, 2023
- Committee Members:
- Farshad Rajabipour, Major Field Member
Sven Bilén, Outside Unit & Field Member
Barry Earl Scheetz, Special Member
Gordon Warn, Major Field Member
Aleksandra Radli¿ska, Chair & Dissertation Advisor
Patrick Fox, Program Head/Chair - Keywords:
- Geopolymer Lunar Concrete
Moon
Concrete
Durability
Lunar Simulant
Gravity - Abstract:
- Concrete materials are a plausible option for constructing various types of infrastructure required on the lunar surface to successfully maintain a human presence. The National Aeronautics and Space Administration (NASA) will embark on the next era of human space exploration with the Artemis program, which seeks to maintain a human presence on the Moon and one day proceed to Mars. A priority for constructing infrastructure on the Moon is to minimize the reliance on supplies from Earth and use the resources available on the lunar surface. While a traditional portland cement concrete material is not feasible on the lunar surface due to a lack of required calcium, alternative concrete material options, such as geopolymer concrete, have advantageous properties for the lunar surface. However, geopolymer lunar concrete has not been heavily researched, and much still needs to be understood and addressed to progress the material toward implementation. Geopolymer lunar concrete uses the lunar regolith in the as-found condition and can be mixed with an alkaline solution (typically a combination of sodium silicate and sodium hydroxide) to create the material. A challenge for all concrete materials on the Moon is the extreme environmental conditions, which include extreme temperature ranges, a hard vacuum, reduced gravity, and solar radiation. To address the environmental condition of reduced gravity, an experiment was conducted on the International Space Station (ISS) to progress the use of concrete materials focused on in-situ resource utilization. The experiment concentrated on understanding gravity’s influence on the microstructure and micromechanical properties of a portland cement and lunar regolith simulant composite. Samples were prepared on Earth and by astronauts on the ISS to allow for hydration at microgravity, lunar gravity, Martian gravity, a statistical point at 70% of terrestrial gravity, and Earth’s gravity. A centrifuge was used on the ISS to create the partial gravity levels, and the samples were analyzed on Earth by statistical nanoindentation to understand the micromechanical properties. Whereas portland cement will not be used on the lunar surface, understanding differences induced by various gravitational forces is likely transferable to other concrete-like materials. The micromechanical properties showed no differences, but other microstructural differences may transfer to the macroscale properties of the material and alter its performance. One of the limitations in progressing the use of geopolymer lunar concrete is the inability to use actual lunar regolith. For research applications, lunar regolith simulants have been created. There have been over 50 manufactured simulants from various parts of the world. As such, there are variations in the fidelity of the material that influence research applications. To that end, five lunar regolith simulants were acquired, with four representing the mare regolith and one representing the highlands regolith. The simulants were characterized in detail through laser particle size distribution, X-ray fluorescence, X-ray diffraction, and reactivity testing. The characterization data were compared to compiled Apollo data. Geopolymer lunar concrete samples were created with all five lunar regolith simulants for compressive strength testing, mercury intrusion porosimetry, and Fourier-transform infrared spectroscopy. Results of the experimental program note that no lunar regolith simulant is a perfect match to the actual lunar regolith and conclusions should be met with caution when performing research with simulants. One of the steps in developing geopolymer lunar concrete was understanding how the curing environment and mixture design influence the material’s compressive strength and microstructural development. Building in the hard vacuum environment of the lunar surface is not feasible for concrete materials with an aqueous solution, so conditions suitable for curing could be maintained through a temporary environmental enclosure. Infrastructure would be constructed autonomously through additive manufacturing (3D printing) techniques. Samples were cast to understand how reduced pressures, different temperatures, and different solution-to-simulant ratios influence the compressive strength development of the material. Furthermore, samples were cast to understand the importance of cure time in the environmental enclosure and what happens to them once exposed to a vacuum environment. The results of the reduced pressure curing showed trends in the material’s compressive strength, which was further investigated through a central composite design study. The results of the study are an essential step towards setting benchmark conditions needed within the environmental enclosure and for additive manufacturing with the material. The printability of the geopolymer lunar concrete must be kept in mind in efforts to scale up towards 3D printing with it. Printability refers to the material’s pumpability, extrudability, and buildability; some essential characteristics are quick strength development and setting after deposition. Admixtures are often used within concrete mixtures to achieve desired mixture characteristics. However, such admixtures would not readily be available on the lunar surface and, thus, alternative methods to promote curing are needed. A novel study was performed on providing an initial rapid cure of the geopolymer lunar concrete mixture through microwave radiation. Variations of supplemental curing techniques were tested following the microwave curing regime. Lastly, the material’s durability under relevant exposure conditions is of interest. Geopolymer lunar concrete samples were exposed outside the ISS in the zenith direction for approximately six months to understand the material’s durability in a space environment. Furthermore, one of the pieces of infrastructure that will be required on the lunar surface is landing pads. A set of geopolymer lunar concrete samples were exposed to a subscale simulated rocket engine at the Plasma Torch Test Facility at NASA Marshall Space Flight Center. Overall, these studies provide needed knowledge on geopolymer lunar concrete and help progress the material’s potential use on the lunar surface.