Researchers from Northwestern University have developed a structural material, called sulfur concrete, that is based entirely on raw materials that are abundant on Mars. Potentially, it could be used for constructing buildings on the Red Planet. See also: Buildings; Mars; Structural materials

Sulfur concrete is not new, as it was developed in the mid-1970s. It consists of elemental sulfur and aggregate (sand, gravel, or crushed stone) that have been heated to above 115°C—the melting point of sulfur. After cooling, the material achieves high strength and has good chemical resistance. In addition, sulfur concrete is thermoplastic, which allows it to be recyclable on reheating. However, its low melting temperature is also a disadvantage in that a fire could cause the meltdown of a building constructed from it. See also: Gravel; Recycling technology; Sand; Stone and stone products; Sulfur

In ordinary concrete, the cement hardens through a chemical reaction with water to strengthen and bind the embedded materials. In contrast, sulfur concrete does not require any water, which is totally or nearly absent from the Martian surface. However, Mars has an abundant supply of sulfur in the form of sulfates and sulfides as well as regolith (soil) for use as aggregate. See also: Cement; Concrete; Regolith

For their experiments, the researchers used commercially available sulfur and simulated Martian soil for the aggregate. The mineral content of the simulated soil consisted of silicon dioxide, titanium dioxide, aluminum oxide, and ferric oxide, with lesser amounts of iron, magnesium, calcium, sodium, potassium, and manganese oxides. A mixture of 50 percent sulfur and 50 percent Martian soil with a particle size of 1 mm resulted in an optimal product that had greater compressive strength (the most important property of hardened concrete) than regular concrete. It also had about twice the compressive strength of sulfur concrete made with sand aggregate. The researchers believe that the strength improvement is the result of chemical reactions during heating of the sulfur concrete, but that inference still needs to be tested. See also: Mineralogy of Mars; Strength of materials

Before a colony for housing humans or robots is built on Mars, a number of practical considerations will need to be solved, such as the need for a Mars-based chemical plant to produce elemental sulfur from sulfates or sulfides and perhaps for a 3D printing method for constructing buildings. Nevertheless, in terms of raw materials and energy requirements, Martian sulfur concrete seems a promising construction material. See also: 3D printing applications in space