Can moon soil be used to construct buildings? • Earth.com
If humanity ever decides it’s time to move to another planet, people will need to build infrastructure there, in the form of buildings, housing, and rocket landing pads. This represents a considerable technical challenge because current construction materials on Earth, such as cement, are far too heavy to be included in the payload of a space rocket. And we don’t even know if they would work under the temperature and pressure conditions encountered by aliens. Future residents of other planets will most likely need to use locally available materials to build their infrastructure.
This has led researchers to explore ways to use clay topsoil from the Moon and Mars as a base for space cement. There is plenty of dirt available on these bodies, but this will need to be bound to form concrete using a binder that works in alien conditions. One of the requirements for such an unusual construction material is that it must be durable enough for the vertical launch pads needed to protect artificial rockets from whirlwinds of rocks, dust and other debris during liftoff or of landing. Most conventional building materials, such as ordinary cement, are not suitable for spatial conditions.
“If we are going to live and work on another planet like Mars or the Moon, we have to make concrete. But we can’t take bags of concrete with us – we have to use local resources,” said Norman Wagner from University of Delaware.
Researchers are exploring ways to use clay-like topsoil materials from the moon or Mars as the basis for an extraterrestrial cement that can be used as a binder to form concrete for construction purposes. Maria Katzarova, a former associate scientist and member of Wagner’s lab at UD, wondered if it would be possible to activate simulated lunar and Martian soils to become concrete-like building materials using the chemistry of geopolymers.
Geopolymers are inorganic polymers formed from aluminosilicate minerals found in common clays all over Earth, as well as in extraterrestrial soils such as those found on the moon and Mars. When mixed with a high pH solvent, such as sodium silicate, the clay dissolves, releasing the aluminum and silicon within to react with other materials and act as a binding, the same way cement does on Earth.
Katzarova pitched the idea to NASA and secured funding through the Delaware Space Grant Consortium to test this idea, with the help and expertise of Jennifer Mills, then a PhD student at UD, who studied Earth geopolymers. for his doctoral thesis. The researchers systematically prepared geopolymer binders from a variety of simulated lunar and Martian soils, then compared the characteristics and performance of the materials, which had never been done before. Their findings were published in the journal Advances in space researchearlier this year, and were also highlighted recently in the review Advances in Engineering.
“It’s not a trivial thing. You can’t just tell me to give me old clay, and I’ll make it work. There are parameters, chemistry that you have to worry about,” said said Wagner.
The researchers mixed various simulated soils with sodium silicate, then poured the geopolymer mixture into ice-cube molds and waited for the reaction to occur. They found that three simulated lunar soil samples and one Martian soil sample were successfully converted into geopolymer binders using this method. After seven days, they measured the size and weight of each cube, then ground it to understand how the material behaves under load. Specifically, they wanted to know if slight differences in chemistry between the simulated soils affected the strength of the material.
“When a rocket lifts off, there’s a lot of weight pressing down on the landing strip and the concrete has to hold, so the compressive strength of the material becomes an important measure,” Wagner said. “At least on Earth, we were able to make materials in small cubes that had the compressive strength to do the job.”
The research team also subjected the samples to environmental conditions commonly found in space, including vacuum and low and high temperatures. They found that, in a vacuum, some of the material samples formed cement, while others were only partially effective. Overall, the compressive strength of geopolymer cement decreased when formed under vacuum, compared to geopolymer cubes hardened at room temperature and pressure.
“There’s going to be a trade-off between whether we have to cast these materials in a pressurized environment to ensure the reaction forms the strongest material or whether we can 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 doctorate in chemical engineering at UD in May 2022 and now works at Dow Chemical Company.
Temperature also played an important role in determining the characteristics of geopolymer cement. At low temperature of about -80ohC, the geopolymer materials did not react at all and did not set.
“This tells us that we might need to use some sort of accelerator to achieve the strength we see at room temperature,” Mills said. “Maybe the geopolymer needs to be heated, or maybe we need to add something else to the mix to trigger the reaction for certain applications or certain environments.”
At high temperatures of about 600ohC, all samples using lunar soils were stronger than at room temperature. This was not surprising, Mills said, given that the reactions were so slow at low temperatures. The research team also found changes in the physical nature of geopolymer cement under conditions of increased temperature.
“The geopolymer bricks became much more brittle when we heated them, shattering instead of compressing or breaking in half,” Mills said. “That could be important if the material is going to be subjected to any kind of external pressure.”
Based on their findings, the researchers said the chemical composition and particle size of soils can play an important role in the strength of these materials. For example, smaller particles increase the surface area available for chemical reactions, which makes soils easier to react and potentially leads to greater overall material strength.
Two of Wagner’s current graduate students are also exploring ways to use geopolymer cements to 3D print homes and activate geopolymer materials using microwave technology. The work is a collaborative project, funded by the National Science Foundation, with researchers from Northeastern and Georgetown universities. Similar to the microwaves you use to heat up your morning coffee, microwave heating can speed up the curing of geopolymers and may one day provide a way for earth builders – or astronauts – to harden geopolymer concrete in a targeted way. .
By Alison Bosman, Terre.com Personal editor