Sulphur Concrete
Concrete is made of sand or larger particles bound together by some substance. Regular concrete will cure very slowly in the Martian CO2 atmosphere.
This study: [1] talks about concrete using molten sulphur as the binder, in a CO2 rich atmosphere.
Discussion
Note that sulphur melts at 120 degrees C, so this should be quite doable with modest equipment, or even a solar thermal farm.
Waterless concrete can be produced from sulfur and regolith. Some applications have been found on Earth, in particular for conditions requiring acid protection.
The ultimate strength and tensile strength was found to be best at a mixing ratio of 50% sulfur and 50% JSC Mars-1A regolith simulant sieved to a maximum particle size of 1 mm. The concrete was found to have a compression strength of > 50 MPa, a flexural strength of 1.75 MPa, and a splitting tensile strength of 3.9 MPa. This is approximately twice as strong as normal concrete.
Utilizing sulfur-regolith concrete is possible on Mars, but not the Moon. On the moon, the concrete mass would be gradually lost due to sublimation of sulfur in vacuum, and the large temperature swings between lunar day and night which compromise the structure. Sulfur-regolith concrete is stable under Martian conditions and would not experience a loss in mass due to sublimation.
Mars is considered a sulfur-rich planet (sulphates are common), but it in unclear where rich sulphur deposits may be. Elemental sulphur has been found in only tiny amounts. It is expected that processing of raw materials will be needed before it is in a form suitable for the production of sulfur concrete.
An important disadvantage of sulfur cement is that is is not fireproof. The sulfur used as binder can melt at higher temperatures, and may emit large amounts of smoke.
