Martian bricklayers

If you've ever mused on the notion of settling on Mars, you might be wondering what the first settlers would use as building materials. Now, a team from the University of California San Diego, in research funded by NASA, have shown that it is possible to make brick-shaped parts from a Martian soil simulant without having to bake them and without any additives simply by squeezing them hard. Qiao et al., Sci Rep (2017); DOI: 10.1038/s41598-017-01157-w]

The work might eventually be used in the planning of manned mission to Mars set for 2033. "The people who will go to Mars will be incredibly brave. They will be pioneers. And I would be honored to be their brick maker," explains materials scientist Yu Qiao. Of course, using Martian soil to make bricks seems obvious and others have come up with brick fabrication schemes that might be used in the Red Planet. However, with minimal resources to manufacture bricks, the likelihood of nuclear-powered kilns or complex polymerization chemistry are unlikely to be viable in the near future.

Now, the UC San Diego team in attempting to minimize the amount of polymer additive needed by one of these schemes has serendipitously found that no such chemistry is needed to convert organic matter found on Mars into a polymerized binding agent for bricks. Instead, they have found that a simulated Martian regolith, or soil (a material known as Mars-1a, comprising glassy volcanic ash from Hawaii) will form solid bricks without additives and without heating or baking. The solution was to use a flexible container and to apply sufficient pressure to the simulant within; pressures of 100-400 megapascals are required.

The researchers describe how their process forms small round pallets of the simulant, which can then be cut into bricks. They point out that iron oxide, which gives the surface of Mars its familiar reddish hue, and is present in the Mars-1a simulant material is acting as an endogenous binding agent. When the team analyzed Mars-1a closely they confirmed that rocky basalt particles are effectively coated with nanoscopic iron oxide particles. The clean crystalline facets of this coating can bind to other facets when pressure is applied allowing the particles to fuse. The resulting material was found to be stronger than steel-reinforced concrete in the team's strength tests. The next step will be to demonstrate that bigger breaks are feasible before sending the bricklayers to the Red Planet.

"We are working on scaling up from inch-sized lab specimens to foot-sized structural parts," Qiao told Materials Today.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".