Infrastructure that isn't currently exist are needed for sustained space exploration.
When construction materials are too large to fit in your carry-on, where do you turn?
We need to make concrete if we want to live and work on other planets. We need to use local resources, but we can't take bags of concrete with us.
The basis for extraterrestrial cement could be derived from clay-like materials from the moon or Mars. The extraterrestrial starting materials need to be glued together through chemistry. One requirement for this out-of-this-world construction material is that it must bedurable enough for the vertical launch pads needed to protect man-made rockets from swirling rocks, dust and other debris. Ordinary cement can't be used under space conditions.
A group of people from the University of Dayton are working on a project to convert lunar and Mars soils into cement that is good for the environment. The results of the research team's work were reported in Advances in Space Research. The work was highlighted in an article.
The cement is made of geopolymer cement.
From Newark, Delaware's White Clay Creek to Africa, aluminosilicate minerals are used to make geopolymers. When mixed with a solvent that has a high pH, the clay can be dissolved, freeing the aluminum and Silicon inside to react with other materials.
Common clays can be found in the soil on the moon.
Maria Katzarova wondered if it was possible to make concrete-like building materials out of moon and Martian soils. She got funding from the Delaware Space Grant Consortium to try and get the help and expertise of a University of Delaware graduate student in the field. The researchers prepared binders from different soils in the same way and compared them to each other.
This is a big deal. I will make it work if you give me any old clay. "Chemistry is something that you have to worry about."
The researchers waited for the reaction to occur after mixing various soils with sodium silicate and casting the mixture into ice cube-like molds. They measured each cube and then crushed it to understand how it behaves under load. They wanted to know if there were differences in chemistry between the simulations.
When a rocket takes off there's a lot of weight pushing down on the landing pad and the concrete needs to hold. We were able to make materials in small cubes that were strong enough to do the job.
The amount of material astronauts would need to take with them to land on the moon or Mars was calculated by the researchers. The estimated amount is within the range of a rocket's total weight.
Space conditions are imagined.
The samples were subjected to a number of different environments in space. The information they found was useful.
Some of the material samples formed cement, while others were only partially successful. The compression strength of the cement decreased when it was vacuumed, compared to when it was cured at room temperature and pressure. New considerations are raised based on the material's purpose.
There is a tradeoff between whether we need 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.
The materials didn't react at all under low temperatures.
"This tells us that we might need to use something to achieve the strength we see at room temperature." Maybe we need to add something else to the mix to get the reaction we want.
The researchers found that the samples got stronger at high temperatures. Mills said that it was not surprising given how low the temperatures were. Changes in the physical nature of the cement were seen by the research team.
Mills said that the bricks became brittle when they were heated up. It's important if the material is going to be subjected to external pressures.
The researchers said that chemical composition and particle size may have an effect on material strength. Smaller particles make them easier to react and could lead to greater material strength. It can be difficult to estimate the amount of aluminosilicate in the starting materials when there are small concentrations of these materials in the solution.
What is the meaning of it all?
Amazon doesn't offer two-day delivery to space, so it's up to the designers to come up with the right formula. It's important that astronauts understand what affects material strength since they'll be using different materials on different planets.
The results can be used to makegeopolymer cements that are better for the environment and can be obtained from a wider variety of local materials. The water used to make traditional cement is not used in the reaction. Water can be recovered and reused in water limited environments.
Two current graduate students are looking at ways to use microwave technology to create 3D-print houses and usegeopolymer cements to do so. Researchers at Northeastern and Georgetown universities collaborated on the project. Microwave heating may one day provide a way for astronauts to curegeopolymer concrete in a targeted way, similar to the way microwaves speed up coffee.
More information: Jennifer N. Mills et al, Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization, Advances in Space Research (2021). DOI: 10.1016/j.asr.2021.10.045
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