So, compared to ground-mixed cement, space-mixed cement is more uniform in density (which makes it stronger), but it's also more porous (which makes it weaker). Or, as Radlinska explained it, "we have opposite effects occurring concurrently!"
In order to determine whether the more-uniform-yet-more-fluffy space cement is stronger than its ground-mixed sibling, Radlinska says they'll need to destroy the samples later in 2019, after concluding their microstructural analysis. This will let them determine whether uniformity or porosity plays a bigger role in the cement's overall strength.
Making cement on other worlds
The obvious benefit of learning how Earth-made and space-made cements differ is that it can help researchers identify and address exactly how gravity impacts the cement manufacturing process. Though this hasn't been a concern during the past five millennia, considering the dramatic advances we've seen in human spaceflight in just the past 50 years, we'll want to know these things before we start using cement on other worlds.
"On missions to the Moon and Mars, humans and equipment will need to be protected from extreme temperatures and radiation, and the only way to do that is by building infrastructures on these extraterrestrial environments," says Radlinska. "One idea is building with a concrete-like material in space. Concrete is very sturdy and provides better protection than many materials."
Concrete, in a basic sense, is simply aggregates like sand, gravel, rocks — or a mixture of all three — glued together with cement. The benefits of concrete are that it's cheap, straight-forward to make, and can be formed into just about any shape or structure to suit specific needs.
"Concrete is an excellent insulator and radiation shield, hence its used for storage of nuclear waste," says Radlinska. "The future shelters on [Mars and the Moon] would require thick cover, but a concrete-like binder can be effectively used even in the extraterrestrial extreme conditions."
And as an added benefit, the gravel and rocks used to make concrete don't necessarily need to come from Earth. Because it's the cement that's actually binding these aggregates together, we should be able to create a form of concrete using aggregates readily available on other worlds, such as lunar regolith — also known as Moon dust.
Because regolith is made of notoriously jagged and fine dust grains, Radlinska says it could potentially help decrease the porosity and increase the strength of the resulting concrete. This is why they've already carried out some preliminary work that focuses on lunar regolith. She says they are currently submitting that work for publication.
So, by mixing cement in space for the first time, researchers have not only showed they can do it, but they've also set up future avenues of research that will help us fine-tune space cement to fit our specific extraterrestrial needs.
"We confirmed the hypothesis that this can be done," says Radlinksa. "Now we can take next steps to find binders that are specific for space and for variable levels of gravity, from zero [gravity] to Mars [gravity] and in between."
Although the researchers are remaining tight-lipped about what specific binders might work best for space cement, Radlinska says, "We have several ideas and [a] working hypothesis of what the next 'best' material would be. We can't disclose these just yet."
