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Extraterrestrial cement [udel.edu]:

Sustained space exploration will require infrastructure that doesn't currently exist: buildings, housing, rocket landing pads.

[...] "If we're going to live and work on another planet like Mars or the moon, we need to make concrete. But we can't take bags of concrete with us — we need to use local resources," said Norman Wagner, Unidel Robert L. Pigford Chair of Chemical and Biomolecular Engineering at the University of Delaware.

Researchers are exploring ways to use clay-like topsoil materials from the moon or Mars as the basis for extraterrestrial cement. To succeed will require a binder to glue the extraterrestrial starting materials together through chemistry. One requirement for this out-of-this-world construction material is that it must be durable enough for the vertical launch pads needed to protect man-made rockets from swirling rocks, dust and other debris during liftoff or landing. Most conventional construction materials, such as ordinary cement, are not suitable under space conditions.

UD's Wagner and colleagues are working on this problem and successfully converted simulated lunar and Martian soils into geopolymer cement, which is considered a good substitute for conventional cement. [...]

Geopolymers are inorganic polymers formed from aluminosilicate minerals found in common clays everywhere from Newark, Delaware's White Clay Creek to Africa. When mixed with a solvent that has a high pH, such as sodium silicate, the clay can be dissolved, freeing the aluminum and silicon inside to react with other materials and form new structures — like cement.

[...] The researchers mixed various simulated soils with sodium silicate then cast the geopolymer mixture into ice-cube-like molds and waited for the reaction to occur. After seven days, they measured each cube's size and weight, then crushed it to understand how the material behaves under load. Specifically, they wanted to know if slight differences in chemistry between simulated soils affected the material's strength.

"When a rocket takes off there's a lot of weight pushing down on the landing pad and the concrete needs to hold, so the material's compressive strength becomes an important metric," Wagner said. "At least on Earth, we were able to make materials in little cubes that had the compressive strength necessary to do the job."

Under vacuum, some of the material samples did form cement, while others were only partially successful. However, overall, the geopolymer cement's compressive strength decreased under vacuum, compared to geopolymer cubes cured at room temperature and pressure. This raises new considerations depending on the material's purpose.

"There's going to be a tradeoff between whether we need to cast these materials in a pressurized environment to ensure the reaction forms the strongest material or whether can we get away with forming them under vacuum, the normal environment on the moon or Mars, and achieve something that's good enough," said Mills, who earned her doctoral degree in chemical engineering at UD in May 2022 and now works at Dow Chemical Company.

Journal Reference:
Jennifer N.Mills, MariaKatzarova, and Norman J.Wagner, Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization, Adv Sp Res, 69, 1, 2022. DOI: 10.1016/j.asr.2021.10.045 [doi.org]

Original Submission