Sorel cement, also called magnesium oxychloride cement (MOC), is a non hydraulic cement made from a mixture of magnesium oxide and magnesium brine. It was discovered by the French engineer Stanislas Sorel in 1867. It has a maximum compressive strength of over 10000 PSI compared to 2000 PSI for common Portland cement and has excellent shear strength. It has found limited use due to it's very poor water resistance and is commonly used artificial stone, wallboards, and as a binding agent in grindstones. On Mars it would be used to prepare concrete and mortar.
As a construction material on Mars, the water resistance is not a serious issue due to the lack of liquid water on the surface. The chief advantage over other building materials is that the ingredients can be produced with much less energy than other alternatives. Both MgO and MgCl2 can be produced from magnesite, a naturally occurring mineral made up of magnesium carbonate. The MgO is produced by calcination of magnesite at 500C. The magnesium chloride is produced from the same material by dissolution and decomposition in hydrochloric acid. While Martian atmospheric pressure is not enough to support liquid water at any temperature, the MgCl brine at about 4 molar concentration may be liquid near freezing temperatures, allowing the curing process to proceed in the Martian atmosphere without the need for pressurized forms.
Cured Sorel cement has a pH in the range of 10-11, which makes it compatible with glass fiber admixtures. Such an admixture can possibly add significant tensile strength as well as changing the mode of failure to permit it's use in pressurized structures.
As of September 2011, research is being conducted on the curing properties of Sorel cement in the Martian environment in the Civil Engineering department at California State University, Fullerton. This research will also study the flexural and tensile strength of MOC with chopped strand fiberglass admixture to test the possibility of using MOC for pressurized structures.
Li, Zongjin (2011) Advanced Concrete Technology, John Wiley & Sons, Inc.