Concrete

Concrete is a well known material on Earth, and would be useful for building settlement facilities such as houses and infrastructure elements. It has excellent characteristics for protection against radiation and small meteorites. Possibly, concrete can be made in situ on Mars, using local resources. Concrete is usually a mixture of water, Portland cement, sand and stone in various proportions. Portland Cement ingredients may not exist on Mars, hence other types of binders have been explored over time. The density of concrete depends on the mix and the density of the aggregate, but is usually about 2400 kg/m3. Concrete has an embodied energy of about 1,1 to 2 MJ/kg. Steel Rebar is usually required and increases the embodied energy of the material.

Concrete has the great advantage that it can be cast in place into practically any shape. It is much cheaper than steel, although is is also much less tough. It provides much better radiation protection than steel.

Mix

Concrete preparation follows certain ratios for the main ingredients.: Cement, Sand and Aggregate. (M) stands for mix and the number is the compressive strength in MPa (N/m2) after 28 days of curing. Water is usually mixed in at about 0,45 per volume of the cement. There proportions are for volumes, nor for masses.

Grades of Concrete	Ratios of Concrete mix design(Cement:Sand:Aggregate)
M5	1:5:10
M7.5	1:4:8
M10	1:3:6
M15	1:2:4 (most common mix)
M20	1:1.5:3
M25	1:1:2
M30	1:0.75:1.5
M35	1:0.5:1
M40	1:0.25:0.5

Cement

Cement is the binder in concrete. There are many possible materials for this function. On Earth the most common binders are lime and calcium silicate, than produce hydrate when mixed with water, hence the name hydraulic cements.

Hydraulic (Portland) cement

There seems to be plenty of water on Mars, but hydraulic cement also requires calcium, silicon oxide (sand) and aluminum oxide. It is unclear whether these substances can be found on Mars in a form that allows a simple production process.

Sorel Cement

Sorel cement is magnesium based cement, a non hydraulic cement made from a mixture of magnesium oxide and magnesium brine. It has poor water resistance but excellent sheer strength.

Sulfur cement

Waterless concrete can be produced from sulfur and regolith<ref>https://arxiv.org/pdf/1512.05461.pdf "A Novel Material for In Situ Construction on Mars:

See Sulphur Concrete for more information.

Starch concrete

On Mars, a tough concrete can be made out of starch mixed with regolith, (and with a pinch of salt). See StarCrete for more information.

Sand and stone

Sand and stone are common on Mars. Most types of volcanic rock are compatible with concrete.

Reinforcement

The stability of concrete structures can be increased significantly by glass fibers or reinforcing steel.

Concrete is almost always reinforced with rebar, steel bars that give it strength in tension.
Composite basalt fiber rebar is available on Earth, but problems with installation may reduce its adoption. The binder required for the composite rebar may be expensive, in embodied energy terms.