Solidia Technologies, a company established to commercialise the work of Rutgers University in New Jersey, has developed a cement making process that the company says produces 70% less CO2 emissions than conventional cement manufacture while producing a product which is equally as strong.

Conventional “Portland” cement is made by heating limestone (calcium carbonate) with other materials such as clay to 1450 °C in a kiln. This releases CO2 from the calcium carbonate to form calcium oxide (quicklime), which then chemically combines with the other materials to produce a hard “clinker” which is ground with gypsum to produce the cement.

Worldwide, around 4.2 trillion kilograms of cement is produced annually – and making each kilogram of cement releases more than 0.5 kilogram of CO2 into the atmosphere.

Rutgers researchers had found that, if the limestone is replaced by a mineral called wollastonite, no carbon dioxide is released during manufacture. But wollastonite is not as cheap and plentiful as limestone.

Wollastonite cement has a lot less calcium than Portland cement. So Solidia simply reduced the amount of calcium carbonate (limestone) and increased the amount of clay in the mix, omitting the wollastonite. With less limestone, the process uses less heat and, so, less fuel as well as significantly reducing CO2 emissions.

Unlike Portland cement, Solidia’s product doesn’t harden after simply adding water. Instead, it absorbs CO2 from the atmosphere – capturing about 240 kilograms of CO2 for every 1,000 kilograms of cement.