When humans get to space, they will need somewhere to live. For such a place to be viable Earth-made cement would be ideal. But could it be made in space?
Concrete in space
That is the question a recent investigation on the International Space Station examined. The astronauts performed cement solidification in microgravity to see how it turned out.
"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," said principal investigator Aleksandra Radlinska of Pennsylvania State University. "One idea is building with a concrete-like material in space. Concrete is very sturdy and provides better protection than many materials."
The project was called Microgravity Investigation of Cement Solidification (MICS) and it saw researchers mix tricalcium silicate (C3S) and water outside of Earth's gravity for the first time. MICS investigated whether solidifying cement in microgravity would result in unique microstructures.
It also provided the first comparison of cement samples processed on the ground and in microgravity. Scientists know pretty much all there is to know about concrete on Earth, but do not yet know what happens to the material in space.
"How will it harden? What will be the microstructure?" said Radlinska. "Those are the questions we're trying to answer."
The researchers explored a series of mixtures that varied the different elements necessary for cement creation. On first evaluation, the samples processed on the space station were very different than those processed on Earth.
One such primary difference was the presence of more open spaces. "Increased porosity has direct bearing on the strength of the material, but we have yet to measure the strength of the space-formed material," said Radlinska.
"Even though concrete has been used for so long on Earth, we still don't necessarily understand all the aspects of the hydration process. Now we know there are some differences between Earth- and space-based systems and we can examine those differences to see which ones are beneficial and which ones are detrimental to using this material in space," said Radlinska. "Also, the samples were in sealed pouches, so another question is whether they would have additional complexities in an open space environment."
The researchers are now evaluating cement samples containing simulated lunar particles. However, showing that concrete can be developed in space was an important step toward achieving the first structure built on the Moon using materials from the Moon.
"We confirmed the hypothesis that this can be done," Radlinska said. "Now we can take next steps to find binders that are specific for space and for variable levels of gravity, from zero g to Mars g and in between."
The results were submitted in a paper published in Frontiers in Materials.