Here’s why NASA astronauts are mixing cement up in the ISS

NASA astronauts aboard the International Space Station are conducting several experiments relating to cement, in pursuit of discovering how the material can be used in space.

Astronauts often conduct several hundred experiments during their time in the ISS in order to identify what the effects of microgravity have on certain Earth-bound phenomena and materials. In this particular testing, they wanted to learn how cement works in space.

In fact, NASA has a program dedicated to the study of cement in microgravity and space, which the space agency calls Microgravity Investigation of Cement Solidification or MICS, which is mainly focused on examining how we might build habitats or other structures in microgravity.

As part of MICS, and a related study called MVP Cell-05, NASA and Pennsylvania State University teamed up with astronauts on the ISS to mix concrete.

Particularly, cement is of interest because aside from its insulative quality, concrete can also provide protection from radiation, and its structural strength provides protection from meteorite impacts, which makes it a likely choice for space and microgravity construction.

Furthermore, cement has been known to give structural integrity to buildings and other Earth structures, making them strong and sturdy enough that could last through several disasters. Some olden structures have been found to be held together by cement that had kept them intact and still standing today.

However, before pushing forward with the material, NASA first wants to learn about how it would interact in an environment outside Earth.

“How will it harden? What will be the microstructure?” said Aleksandra Radlinska, principal investigator of the experiment at Pennsylvania State University and for MICS and MVP Cell-05. “Those are the questions we’re trying to answer.”

Some of the answers to those questions and results are published in Frontiers in Materials, and is titled, “Microgravity Effect on Microstructural Development of Tri-calcium Silicate (C3S) Paste.”

An artist’s illustration of the ingredients that make cement.
Source: NASA

To be specific, researchers were more intent in studying the composition in cement that holds everything together.

Concrete itself is a mixture of an aggregate, which consists of sand, gravel, and rocks, and are held together with cement, which comes in two types: Portland cement or geopolymer cement. Combine it all with water and when it cures or hardens properly, it’s an extremely strong substance.

“Our experiments are focused on the cement paste that holds the concrete together. We want to know what grows inside cement-based concrete when there are no gravity-driven phenomena, such as sedimentation,” said Radlinska.

In the MICS experiment, the astronauts had a number of packets of cement powder, which they added water to. Then they added alcohol to some of the packets at different times, to stop the hydration.

In the second experiment, MVP Cell-05, astronauts also added water to packets of cement, but they used a centrifuge on the ISS to simulate different gravities, including Martian and Lunar gravities.

On the left is C3S paste, a type of cement, mixed at 1G, and on the right is the same paste mixed in microgravity. Both are 56 days old. The large round structures on the right are trapped air bubbles. The microgravity sample on the right also has greater microporosity. Source: Neves et. al., 2019.

Co-Principal Investigator for MVP Cell-05 Richard Grugel said, “We’re already seeing and documenting unexpected results” from the experiments conducted on the ISS.

According to their findings, concrete mixed in micro-gravity had increased micro-porosity due to trapped air bubbles when the cement dried and hardened.

Normally, these air bubbles rise out of the cement mixture as dictated by buoyancy, but that particular phenomenon is not present in microgravity. However, presence of which also indicates that cement made in space are more prone to become less stronger than those typically made on Earth.

Additionally, both MICS and MVP Cell-05 samples showed greater crystallization at 20% more than ground samples. Usually, more crystallization and larger crystals, create more strength. But the greater microporosity in the microgravity samples also creates less dense concrete, which could mean weaker concrete.

Notably, scientists said that this was merely an initial study and they have not yet done any strength tests, so any conclusions on strength are premature.

“What we find could lead to improvements in concrete both in space and on Earth,” added Rudlinska. “Since cement is used extensively around the world, even a small improvement could have a tremendous impact.”

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