Researchers from the University of California, San Diego demonstrated a compaction technique that may someday be used to turn Mars soil into building blocks for the Red Planet. The scientists' new method of applying pressure offers construction possibilities as NASA plans manned Mars missions in the upcoming decades.

In experiments conducted at the university lab, UCSD researcher Dr. Brian Chow and his colleagues Tzehan Chen, Ying Zhong, and Yu Qiao demonstrated unique binding properties of nanoparticulate iron oxide (npOx), a molecule that gives the Mars’ soil its own red hue. The regolith ingredient provides a natural joining agent that could support high-strength “bricks” made from the planet’s surface itself.

Iron oxide, found in rust and prevalent in the soils of Mars, is often considered undesirable, due to the particles’ corrosive properties. The chemical compound has been considered for small-scale applications, like pigmentation or catalysis, but rarely as a building material.

Under Pressure

Researchers compacted Mars simulant under pressure in a cylindrical, flexible rubber tube (shown). The material was then cut into a brick shape. (Credit: UCSD)

The UCSD team compressed the “JSC Mars-1a” simulant, gathered naturally from the south slope of Mauna Kea, Hawaii. The simulant, enclosed in a 30-mm-high rubber tube and fitted with a steel piston of matching size, was compacted at high pressures — the equivalent of a 10-lb hammer dropped from a height of one meter, said Qiao, who first proposed the idea.

The researchers varied force speeds, using the ¾-inch diameter, flat pistons. Slow, quasi-static load rates reached piston velocities of a few millimeters per minute, while high-speed impacts occurred at hammer velocities of a few meters per second.

The simulant’s iron oxide joined together, without polymer binders, to form a brick the size of a fingernail or coin — approximately one centimeter wide, said Chow.

“We found that nanoparticulate iron oxide actually holds this whole thing together,” said Chow. “All that’s simply required is a compression process.”

After the pressure tests, scanning tools revealed that the tiny iron oxide particle’s high surface area enabled easy binding with the simulant’s rocky basalt particles. The UC San Diego engineers discovered that the strength of the brick increased as the polymer content approached zero.

As Strong as Steel

The compacted samples’ permeability reached a measurement on the order of 10−16 m2, close to that of solid rocks, according to a study published in Nature Scientific Reports on April 27, 2017. In the findings, the UCSD researchers compared the bricks’ strength to steel-reinforced concrete.

Previous ideas for Mars habitat construction included nuclear-powered brick kilns or the conversion of Mars compounds into binding polymers. Chow’s compression process is especially valuable for Mars habitat-building applications, given the minimum resources required.

“Compaction strengthening might occur intrinsically in actual red, Martian soil,” said Chow. “If this can be successfully exploited just on the planet using machinery that’s only brought there once and no recurring supplies from the Earth such as polymer binder, or plastics, I think it could reasonably act as a feasible construction alternative.”

Scaling material compaction from the size of a finger to a standard brick, using the UCSD’s current method, would require enormous force, driven by rather large machines the size of hydraulic jacks. According to the team, however, the quasi-static and impact compaction processes are compatible with additive manufacturing, as astronauts could impact a small amount of material upon a substrate, one layer at a time.

In March of 2017, President Trump signed a bill, passed by Congress, directing NASA to send a manned mission to Mars in 2033. The use of local resources is critical, said NASA, for reducing the cost of establishing a human presence on Mars.

"Initial structures will probably be pre-fabricated, but a sustainable presence on the planet will eventually require an ability to produce local building materials and not send them all the way from Earth, 100 million miles away," said Richard McGuire Davis, Jr., Assistant Director for Science and Exploration, Planetary Science Division.

"With this kind of innovative work, Professor Qiao could very well end up being the brick maker for our human explorers on Mars."

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