Jan 12, 2016 | By Alec

Mars has rightly become the number one obsession of NASA, and they are looking at all aspects of the mission to the red planet: not just getting there and back again, but also staying there for longer periods of time. This is why they launched the 3D printed Mars Habitat Challenge for the development of sustainable living solutions that don’t involve hauling tons and tons of materials through space. The first prize of the competition was awarded in September to a house made completely of 3D printed ice, but now an very interesting alternative has been developed by researchers from Northwestern University: a 3D printable concrete made completely from materials found on Mars.

The goal, of course, is to establish a human settlement on Mars in 2025, and everyone who has The Martian knows that won’t be easy. However, this latest innovation by associate professor Gianluca Cusatis, from Northwestern University's McCormick School of Engineering, should make the entire process a lot more practical. Essentially, he and his team have reimagined what concrete actually is. Here on earth, gravel, cement and water are used – materials not exactly common on Mars. Instead, they have used a gravel aggregate and a binding agent – with the latter being molten sulphur, which is found in abundance on the red planet.

The team created a simulation of Martial soil using silicon dioxide and aluminium oxide, along with other components including iron oxide and titanium dioxide.

But there’s more to it than just being practical. In fact, this special concrete mixture has some significant advantages that would doubtlessly interest those innovators seeking to pioneer concrete 3D printing right here on earth. Unlike existing concrete, which takes up to 28 hours to set, this new mixture sets in just two or three hours, making it very suitable for 3D printing. It’s also high resistant to corrosion, being more than twice as strong as typical Sulphur concretes that have been used in previous experiments. In fact, the researchers believe this material could be as strong as the concrete used on skyscrapers (when the gravity on Mars is taken into consideration). While the material’s exact strength is still a bit mysterious, it’s probably a result from the small size of Martian soil particles, combined with a chemical reaction between the soil and sulfur. In fact, when the concrete breaks and is re-melted and re-casted, it becomes even stronger – probably because the particles are even further reduced in size.

The Martian sulphur particles (left) are much smaller than those here on earth.

But the mixture is also more efficient in its materials. "Typical sulphur concrete uses sand, which is inert. It's just filler," Cusatis explained. "In our Martian concrete, the Sulphur is not just glue. It reacts with the minerals in the Martian soil. That completely changes the picture." This interesting material has already led to a paper that has been submitted to the journal Construction and Building Materials, and is currently available here. The paper’s first author is former PhD student Lin Wan and Cusatis’ former research associate Roman Wendner.

All these interesting characteristics pose the question: why aren’t we using this material here on earth? Well, Sulphur concrete has been occasionally used, but it has one main limitation: it is very susceptible to fire and heat. It’s melting point is just 115.2 degrees Celsius (239.4 degrees Fahrenheit), which is easily reached in a burning building. "You want buildings to be fire resistant, so that could be a vulnerability on Mars," Cusatis said of this limitation. "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." However, they will be looking at more ways to make the material more fire-proof in the near future.

While more research will thus be required, Cusatis is hopeful that this work will truly add value to the forthcoming 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.”

 

 

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