NASA is looking toward a future when humans could visit Mars for an extended period, and Elon Musk is promising to send people there in the next decade. Whenever humans do set foot on Mars, they’re going to need someplace to hang their hat (or spacesuit helmet). Concrete could potentially allow explorers to build structures quickly and easily, assuming it sets correctly without Earth gravity. NASA has conducted experiments aboard the International Space Station (ISS) to assess the strength of concrete mixed in space.
Scientists believe concrete could be an ideal material for building on other worlds because it’s durable, offers protection from radiation, and it may be possible to make it using materials present on the moon and Mars. Being able to manufacture building materials at your destination (known as in-situ resources) makes missions cheaper and easier to design because you don’t have to launch as much mass from Earth.
However, there’s a lot we still don’t know about the molecular structure of concrete here on Earth. Concrete is a mixture of sand and gravel with lime or silicate (cement powder). As the cement dissolves in water, it forms crystal complexes that link together the aggregate to make a solid structure. The process of mixing and building with concrete is well established on Earth, but we don’t know how microgravity could affect it. Do we need to modify the ratios? Add additional materials? That’s what the ISS experiment aims to find out.
The experiment, known as Microgravity Investigation of Cement Solidification (MICS), is the first time concrete has been mixed outside of Earth’s gravity. Astronauts aboard the ISS mixed tricalcium silicate and water in varying amounts to create a concrete paste. The astronauts added alcohol to some of the packets to stop the hydration process at set intervals as well. A separate experiment used a centrifuge simulated lunar and Martian gravity on the samples as they mixed.
The experiment confirms that concrete can harden in microgravity, which is a good thing. That means we can build structures with concrete outside of Earth’s gravity. The primary difference is an increase in pores compared with concrete mixed on Earth, and that could reduce the material’s strength. However, lower gravity on the moon or Mars would also put it under less strain. It may be possible to develop different binders that improve the strength of lunar or Martian concrete, and that may even lead to better concrete here on Earth.