Building concrete shelters on mars

From campy favorites like Mars Attacks! to this year's Golden Globe nominee The Martian, Hollywood has long fantasized about putting boots on the Red Planet.

Microscopy images show how much smaller the particle sizes are in the Martian concrete (left) compared to the conventional sulfur concrete (right).

But now that non-profit Mars One plans to establish the first human settlement on Mars in 2025 and NASA hopes to send humans in 2030, this fantasy is quickly becoming a reality.

So a Northwestern Engineering team is getting practical about living on Mars.

Led by Gianluca Cusatis, the team developed a Martian concrete using materials naturally found on the planet. The high-strength concrete can be quickly created and is durable enough to withstand meteorite impacts - a key element needed to create viable shelters for humans.

While typical concrete is made of gravel, cement, and water, the concrete developed by Cusatis, associate professor of civil and environmental engineering at Northwestern's McCormick School of Engineering, comprises materials found on Mars. Instead of gravel, Cusatis used a Martian soil simulant created by NASA.

And instead of water, he used molten sulphur, which is abundant on Mars.

Gianluca Cusatis

The research is described in a paper recently submitted for peer review in the journal Construction and Building Materials and is currently available in pre-print at arxiv.org. Lin Wan, a former PhD student in Cusatis' laboratory, is first author of the paper. Former research associate Roman Wendner, who is currently working at the University of Natural Resources and Life Sciences (BOKU) in Vienna, Austria, is also an author on the paper.

Sulphur-based concrete is not a new idea. Highly corrosion-resistant, it is currently used in non-structural applications, such as pipes and landscaping. But because it is sensitive to heat and fire, it is rarely used for larger projects.

After testing its mechanical properties, Cusastis found that his Martian concrete was more than twice as  strong as typical sulphur-based concretes. In fact, after adjusted for gravity on Mars, its strength is equivalent to concrete used to build skyscrapers on Earth.

''You want buildings to be fire resistant, so that could be a vulnerability on Mars,'' says Cusatis, a concrete expert. ''But for the first settlements, fire won't be the problem. The problems will be having secure shelters and durable buildings that can survive meteorite impacts.''

Cusatis posits that his concrete's strength is due to the small size of particles in the Martian soil as well as a little-understood chemical reaction between the soil and sulphur. His team also found that when the concrete breaks and is re-melted and re-casted, it becomes even stronger, which is most likely due to the additional reduction of the particle sizes.

A block of Cusatis' Martian concrete.

''Typical sulphur concrete uses sand, which is inert. It's just filler,'' Cusatis said. ''In our Martian concrete, the sulphur is not just glue. It reacts with the minerals in the Martian soil. That completely changes the picture.''

While conventional concrete requires 28 hours to develop full strength, Cusatis' Martian concrete takes a mere one-to-two hours. For this reason, he thinks it's a prime candidate for 3-D printing. If 3-D printers are sent to Mars, they could use local resources to print buildings made of Cusatis' sturdy concrete. This would be much more efficient and sustainable than sending materials across the solar system from Earth.

Cusatis emphasizes that his concrete needs to be researched further. He is interested in learning more about the chemical reactions that make it so strong and wants to find ways to make it fire resistant. But with the first trip less than 10 years away, it's not too soon to start preparing for the mission to Mars.

''People now seem serious about going to Mars,'' he said. ''Shelter is a big factor in those plans. Food and shelter are the two things that humans will need most.''