A small step, really? Kinda hard to mix cement without water, and probably not possible in vacuum on the moon nor the near-vacuum of Mars?

By successfully mixing cement in space for the first time, researchers have taken a small step toward building structures on other worlds, such as the Moon and Mars.

Quote Originally Posted by Astronomy
Concrete, in one form or another, has been a staple of human construction for some 5,000 years. Now, researchers have finally brought the ancient technology to outer space. For the first time, scientists have successfully mixed cement — a primary ingredient of concrete — in the microgravity environment aboard the International Space Station (ISS).

As part of an experiment called the Microgravity Investigation of Cement Solidification, researchers sent the basic building blocks of cement — tricalcium silicate, hydrated lime, and distilled water — to the ISS. The ingredients were then mixed in pouches and allowed to harden for 42 days through a process called hydration.

The results show that cement mixed in microgravity can indeed solidify much like it does on Earth. But unlike Earth-made cement, space cement has some unique microscopic features.

Because the new research is the first to compare cement mixed in space to a control batch mixed on Earth, it opens the door to developing better ways to manufacture the substance in various gravitational environments. And if humans are to build a Moon Village or a martian colony in the years to come, we'll likely need to master mixing cement on other worlds.

Interestingly, the researchers discovered that the space station’s lack of strong gravity made the space cement form with a surprisingly uniform density. Meanwhile, back on Earth, the cement mixed in the control experiment developed a more layered structure due to gravity-induced sedimentation. Study author Aleksandra Radlinska, an engineer at Pennsylvania State University, says that the space cement’s more uniform density should actually make it stronger.

But all other things aren't equal when it comes to space cement.

The researchers noted another major microscopic difference: Space cement develops many large air pockets, making it more porous than its Earth-mixed counterpart. According to the research paper, published earlier this year in Frontiers in Materials, air bubbles don't rise to the surface of the freshly mixed space cement like they would on the ground, where buoyancy matters. "Increased porosity has direct bearing on the strength of the material," says Radlinska in a NASA press release, "but we have yet to measure the strength of the space-formed material."