First patented back in 1889 in the US but with a history going back to the Great Wall of China, magnesium-based cements are a lower-carbon than calcium-based cements, such as Portland cement.
Magnesia-based cements replace the calcium oxide of Portland cements with magnesium oxide as the main component. Magnesium silicate cement adds a source of highly-reactive silica (micro silica or silica fume) and was first recorded back in 1889, when a US patent was issued covering the production of a cement from calcined magnesium carbonate and fine silica. This initial patent was followed by several others, before interest in magnesium silicate cements lapsed for several decades.
Interest was rekindled in the second half of the 20th Century, when magnesium silicate cements were viewed as a potentially lower-carbon alternative to Portland cement. They did not reach market maturity, however, in part because the claimed carbon savings were questioned.
Research into the properties of magnesium silicate cements is scarce and variable. It is known that they are of lower alkalinity that Portland cements, suggesting they may be appropriate for use in nuclear waste immobilisation, although no such application is known. Workability is poor, due to the fine nature of the raw materials, while some studies on mechanical performance have indicated the potential to achieve high compressive strengths at 28 days, but this is questioned in other research.
There is also no data on the long-term durability of magnesium silicate cements. Indeed, in comparison to other binders, magnesium silicate cements are much more poorly understood and researched.
The availability of raw materials – particularly deposits of magnesite or magnesium-rich brines – poses an additional challenge, as these are relatively scarce, high cost, and already used in other industries. This compares to the general and widespread availability of limestone for Portland cement productions.
These factors make is unlikely that magnesium silicate cements will ever provide a significant alternative to Portland cement with their use limited to niche markets.