Mars' toxic soil may help make stronger bricks

A PLOS One study found that adding Martian-like perchlorates to regolith simulant, together with the bacterium Sporosarcina pasteurii and guar gum, produced bricks with more than double the compressive strength of samples without perchlorates.

Researchers report that adding perchlorates to Martian regolith simulant improved the strength of laboratory-made bricks. The study, published in PLOS One by teams from the Indian Institute of Science and the University of Florida, tested mixes that included bacteria and a plant-derived adhesive. Most earlier simulants omitted perchlorates because they are a fire hazard, so this experiment intentionally included them. The work focused on biocementation using a Sporosarcina pasteurii strain found in Bangalore soil. Key findings: - Perchlorates, which are toxic and form about 0.5–1% of Martian soil, were added to regolith simulant used for brick tests. - The bacterium Sporosarcina pasteurii formed dense cell clusters and an extracellular matrix (ECM) with "microbridges" when exposed to perchlorate. - Control mixes showed water-only slurries fell apart and mixtures without the full set of ingredients had much lower compressive strength. - Adding guar gum together with the bacterium increased strength by more than three times compared with gum or bacteria used alone. - The strongest tested mix combined bacteria, guar gum, and perchlorate and had more than double the compressive strength of the bacteria-plus-gum mix. - Nickel chloride was tested as a catalyst for ureolysis but was not present in the highest-strength mixture and is not readily available on Mars. Summary: The results indicate that a component long seen as a hazard on Mars, perchlorate, can enhance laboratory biocementation when paired with specific bacteria and a plant-derived adhesive. The authors suggest the ECM and microbridges formed by the bacteria under perchlorate exposure might explain the increased compressive strength, but testing that hypothesis is ongoing. Undetermined at this time.