It remains to be seen whether human settlements on Mars will ever be feasible, or whether they will forever stay in the realm of dreams and science fiction. If Martian cities are to become reality, though, an important first question is what they’ll be made of. Ferrying building materials all the way from Earth would be extremely expensive. Most likely, at least some of the components of future Martian structures would have to be sourced locally.
In its most common terrestrial formulation, concrete is held together with a binder made from cement powder and water. But cement is made mostly from limestone—a mineral not present on Mars—and Martian water is rare and precious. In 2016 Gianluca Cusatis and colleagues turned their attention to a different form of concrete bound together by sulfur, of which Mars has plenty.
Recipes for sulfur concrete date back to the early 20th century, and the material has been produced in moderate quantities on Earth, mostly as a way of getting rid of the excess sulfur left over from oil refining. But mixing up Martian concrete will take more than choosing the right binder—it’s also necessary to check that the physical and chemical interactions between the binder and the Martian regolith endow the concrete with the right material properties.
No samples of regolith—or anything else—have ever been brought from Mars back to Earth. Fortunately, remote measurements by Mars landers have provided enough data on Martian mineralogy that it’s now possible to concoct realistic Martian soil simulants that mimic the regolith in both particle size and composition.
Using the soil simulants, Cusatis and coauthors found that the ideal Martian concrete needs about twice as much sulfur as terrestrial sulfur concrete does. And now his colleague Ange-Therese Akono has taken the investigation a step further by studying the microstructure and mechanical responses of simulated Martian concrete.