A team of NASA-funded researchers from UC San Diego, and led by structural engineer Yu Qiao, made the surprising discovery using simulated Martian soil -- that's dirt from Earth which has nearly the same physical and chemical properties. They found that by compressing the simulant under high pressure, it readily created blocks stronger than steel-reinforced concrete.
This isn't the first time that researchers have attempted to create building materials from native resources on alien worlds. Last year, a team from Northwestern University figured out that you could create concrete by mixing Martian soil with molten sulphur. Qi's own team had previously sought to make bricks from lunar soil material, managing to reduce the amount of binder needed from 15 percent of the final weight to just 3 percent, before turning their attention to the red stuff.
Interestingly, it's the red stuff itself (specifically, iron oxide) that enables Martian soil's compression trick. Iron oxide cracks and shears easily when crushed and its resulting surfaces tend to be angular and flat. When those broad surfaces are subsequently smashed together with sufficient force, they form strong bonds that don't require a binding agent.
While the research team still needs to confirm that the soil property holds up on the macro level (they only made very small bricks during this experiment), Qi figures that if it does, future manned missions to Mars could use soil as the source material for additive manufacturing efforts. And why not? We've already done it with other alien metals.