In order to build homes on Mars, pioneers will ideally rely on ingredients from the Red Planet itself, rather than shipping components across the gulfs of interplanetary space. However, previous research suggested that making bricks from Martian soils was difficult, requiring either a lot of energy to fuse rock together or special liquids brought from Earth to bind grains of soil to each other.
Now, Yu Qiao, a structural engineer at the University of California at San Diego, and his colleagues propose a much easier solution — compressing Martian soil. Their experiments with a simple no-bake recipe utilizing imitation Martian soil resulted in materials similar to dense rock and stronger than steel-reinforced concrete.
Qiao and his team experimented with a widely used Martian soil simulant developed by NASA called “Mars-1a,” which is made up of basalt grains and iron oxide nanoparticles. Based on previous data gathered from the Red Planet, Mars-1a is chemically similar to real Martian soil, or regolith. Prior experiments the team had conducted cementing lunar regolith together with liquid binders gave the scientists the idea to work with Martian soil simulant. “We began with solids that were six percent polymer binding, and they were strong, and then we tried four percent, and two percent, and one percent,” said Qiao.
The researchers compressed Mars-1a between flat pistons, subjecting it to high pressures of 100 to 300 megapascals, which is “roughly equal to the pressure from a 10-lbs. hammer dropped from the height of a yard,” Qiao said. The resulting coin-sized slabs were remarkably strong, “without any heating, without any additives,” he said.
Much of Martian soil is comprised of volcanic rock basalt grains and nanoparticles rich with iron oxides, the same material making up rust, which helps explain why Mars is primarily colored red. (Nanoparticles are particles only nanometers or billionths of a meter large. In comparison, the average human hair is about 100,000 nanometers wide.) When the iron oxide nanoparticles are crushed, “a large amount of tiny, newly cleaved, fresh, flat, clean surfaces result,” Qiao said. “When these surfaces meet each other, they form strong bonds.” The scientists also found that the bricks are nearly as impermeable to gas leaks as solid rock. This suggests walls made of these slabs can keep in the air in Martian habitats.
Future research needs to see if this new technique can scale up to making larger bricks, Qiao said. He added that “everyone, including myself, worries there is no guarantee our results with simulant can be 100 percent repeated with Martian soil. The next logical step after we scale up is to figure out how to experiment directly on Martian soil.”
If this technique does work the same on Martian soil as it does on Mars-1a, there are a number of ways it could help develop habitats on Mars. “We could compact Martian soil into bricks and use the bricks to build up structures, or we could lay down soil layer by layer and compact it layer by layer to build structures without building the bricks,” Qiao said.
The scientists detailed their findings online in the journal Scientific Reports.