NASA has confirmed the hypothesis that cement can be produced in space, through laboratory solidification experiments conducted at the International Space Station.
For the MICS (Microgravity Investigation of Cement Solidification) project tricalcium silicate (C3S) and water outside Earth's gravity were mixed for the first time. The main mineral component of most commercially available cement, C3S controls many of its chemical reactions and properties. MICS explored whether solidifying the cement in microgravity would result in unique microstructures and provided a first comparison of cement samples processed in the soil and in microgravity. The research has been published in Frontiers in Materials.
"On missions to the Moon and Mars, humans and equipment should protect themselves from extreme temperatures and radiation, and the only way to do this is by building infrastructure in these extraterrestrial environments," said lead researcher Aleksandra Radlinska of Pennsylvania State University. "One idea is to build with a cement-like material in space. Concrete is very strong and provides better protection than many materials."
Another significant advantage of cement is that the explorers could theoretically do it with resources available in those extraterrestrial bodies, such as dust on the Moon, also known as lunar regolith. That would eliminate the need to transport construction materials to the Moon or Mars, significantly reducing costs.
For these tests in space, the researchers created a series of mixtures that varied the type of cement powder, the amount and type of additives, the amount of water and the time allowed for hydration. As the powdered cement grains dissolve in water, their molecular structure changes. The crystals form throughout the mixture and intertwine with each other. In the first evaluation, the samples processed at the space station show considerable changes in the microstructure of the cement compared to those processed on Earth. A main difference was the increase in porosity or the presence of more open spaces. "The increase in porosity has a direct relationship with the strength of the material, but we still have to measure the resistance of the material formed in space," Radlinska said.
"Although cement has been used for a long time on Earth, we still do not necessarily understand all aspects of the hydration process. Now we know that there are some differences between Earth-based systems and in space and we can examine those differences to see which are beneficial and which are harmful to use this material in space, "Radlinska said." Also, the samples were in sealed bags, so another question is whether they would have additional complexities in an open space environment. "
The space station's microgravity environment is critical for these first looks at how cement can hydrate on the Moon and Mars. An on-board centrifuge can simulate the severity levels of these extraterrestrial bodies, something that is not possible on Earth. The evaluation of cement samples containing simulated lunar particles processed on board the laboratory in orbit at different levels of gravity is currently underway.
Showing that cement can harden and develop in space represents an important step towards that first structure built on the Moon using materials from the Moon. "We confirm the hypothesis that this can be done," Radlinska said.
"Now we can take the following steps to find binders that are specific for space and for varying levels of gravity, from zero g to Mars g and in the middle."
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