A concrete benefit for space explorers

When humans go to the Moon or Mars, they will have to build safe places to live and work. The most widely used building material on Earth, concrete, can be the solution. It is strong enough and durable enough to provide protection against cosmic radiation and meteorites and it may be possible to manufacture it with materials available on these celestial bodies.

Concrete is a mixture of sand, gravel and rocks bonded together with a paste of water and cement powder. Although this sounds simple, the process is quite complex and scientists are still wondering about the chemistry and microscopic structures involved and how gravity changes can affect the process.

A recent survey of the International Space Station examined the solidification of the cement in microgravity to answer these questions. As part of the Microgravity Project for the Solidification of Cement (MICS), researchers have mixed tricalcium silicate (Ca₃SiO₅ or C₃S) and water outside the gravity land for the first time. The main mineral component of most commercially available cements, the C₃It controls many of its reactions and chemical properties. MICS examined whether the solidification of the cement in microgravity could give unique microstructures and provided a first comparison of the cement samples treated on the ground and in microgravity.

The researchers reported their findings in an article published in Frontiers in Materials, titled "Microgravity Effect on the Development of Tricalcium Silicate Microstructures (C₃S) paste. "

"During Moon and Mars missions, people and equipment will have to be protected from extreme temperatures and radiation, and the only way to do this is to build infrastructure on these extraterrestrial environments," said the researcher. Principal Aleksandra Radlinska of Pennsylvania State University. "One idea is to build a concrete-like material in space, concrete is very strong and offers better protection than many materials."

Another important advantage of the concrete is that the explorers could theoretically build it with the resources available on these extraterrestrial bodies, such as the dust on the Moon, also known as the lunar regolith. This would eliminate the need to transport building materials to the Moon or Mars, which would significantly reduce costs.

Scientists know how concrete behaves and hardens on Earth, but do not yet know if the process is the same in space. "How will it harden, what will be the microstructure?" said Radlinska. "These are the questions we are trying to answer."

The researchers created a series of blends that modify the type of cement powder, the number and type of additives, the amount of water and the time allotted for hydration. As powdered cement grains dissolve in water, their molecular structure changes. Crystals form throughout the mixture and fit into each other. In the first evaluation, the samples processed on the space station show considerable changes in the microstructure of the cement compared to those treated on Earth. A main difference was the increase in porosity or the presence of more open spaces. "The increase in porosity has a direct impact on the strength of the material, but we have not yet measured the resistance of the material formed in the space," Radlinska said.

"Even though concrete has been used for so long on Earth, we still do not understand every aspect of the hydration process.We now know that there are differences between Earth and space systems and we can look at these differences to see which ones are beneficial and which ones harm the use of this material in the space, "Radlinska said. "In addition, the samples were in sealed pouches, so another question is whether they would have additional complexities in an open space environment."

The station's microgravity environment is essential for these early looks on how the cement can hydrate on the moon and on Mars. An on-board centrifuge can simulate the gravity levels of these extraterrestrial bodies, something impossible on Earth. The evaluation of cement samples containing simulated lunar particles processed on board the laboratory in orbit at different levels of severity is in progress.

Showing that concrete can harden and expand in space is an important step towards this first structure built on the Moon using Moon materials. "We have confirmed the hypothesis that this could be done," Radlinska said. "We can now go to the next step to find specific binders for space and varying levels of gravity, from zero to March g and in between."