Carbon-Negative Cement

Novacem is one of several companies making a cement that decreases, rather than increases carbon emissions as part of its manufacture. It absorbs atmospheric carbon. Buildings and building materials are responsible for a signifiant part of the carbon emissions annually:

The carbon dioxide (CO2) released in producing building materials is also substantial and has been targeted as a leading contributor to global climate change. Each ton of cement emits about 800kg (1,763 lb.) of CO2 during manufacture. This is because cement is made from limestone, which releases a huge amount of carbon when it's dug up and then releases even more when it's heated to 1,400 degrees Celsius (2,552 degrees Fahrenheit) [as part of its manufacture.]

[snip]

Novacem's cement, by contrast, is based on magnesium silicates that contain no stored carbon. [Novacem CEO Stuart] Evans says there are world reserves of more than 10,000 billion tons of such silicates, which are the basis for materials such as asbestos and talc. Making cement from these silicates also consumes less energy, because it's only heated to 600 degrees Celsius (1,112 degrees Fahrenheit), and in the process, carbon is absorbed and fixed into the material. The net result: For every ton of Portland cement replaced by Novacem, the atmosphere would be spared up to 850kg (1,873 lb.) of CO2.

Sounds good, but as always in looking at greener materials and processes, what does it cost? It is still the case that virtually no business decision is made on the basis of being greener unless it can also be justified by its concomitant cost savings.