NASA hopes to send a manned mission to Mars within the next two decades. To successfully establish a colony, the first Martians will need to be able to build structures from materials that are resilient and – ideally – sourced locally. Dr. Lin Wan and colleagues at Northwestern University have devised a method for creating concrete on Mars that meets these standards. The team’s breakthrough is made possible through the use of sulfur, an element whose “rotten egg” smell should be familiar to any Earthling.
Unlike concrete on Earth, the Martian concrete is created without the use of water, a key advantage on the dry, cold Red Planet. The concrete making process involves heating sulfur to 240 °C, over twice its melting point. This liquid sulfur is mixed with the abundant Martian soil, then left to cool. The sulfur and soil bind together to create solid concrete. The idea to use sulfur like this has been floating around for at least a century. Due to certain challenges, it has not been widely adopted. Sulfur shrinks as it chemically solidifies, which creates stress that can crack the material. Sulfur concrete was also studied as a building material for lunar bases. Scientists learned that sulfur sublimates – turns from solid straight to gas, skipping liquid phase – in a vacuum, meaning sulfur concrete would dissolve into stardust on the Moon. In the thin atmosphere of Mars, however, conditions would be different.
The researchers at Northwestern emulated Martian soil by creating their own soil composed mostly of silicon dioxide and aluminum dioxide, with a few other appropriate minerals added. After creating their own sulfur concrete blocks, the team gathered data and determined the material’s physical and chemical properties. Following their tests, the team concluded smaller particles are best mixed with an ideal ratio of Martian concrete. “The best mix for producing Martian concrete is 50 percent sulfur and 50 percent Martian soil with maximum aggregate size of 1 mm,” says the team.
The sulfur concrete is also quite strong, boasting a compressive strength rate over twice that of standard concrete for residential buildings on Earth. By melting and resetting the sulfur, the concrete can be recycled as the mission evolves on the ground. Perhaps most importantly, sulfur concrete is exponentially cheaper than the cost of bringing similar materials from Earth. It seems only a matter of time before the Martian concrete is put to work. In the meantime, we eagerly await the blueprints for the first building to be built on Mars.