Carbon Negative Cement

 Cement produces around 5-6% of carbon dioxide emissions because the manufacturing process depends on burning vast amounts of fossil fuels to heat kilns to more than 1,450C. The production of cement also relies on the decomposition of limestone, a chemical change which frees carbon dioxide from the rock as it converts to calcium oxide. The 2 billion tonnes of cement used globally each year creates more emissions of carbon dioxide than the aviation industry. Some projections suggests that there will be a 50% increase in the amount of cement consumed by 2020 further increasing emission of carbon dioxide.

 

An Imperial College London spinoff, Novacem, have developed a new type of cement based on magnesium oxide – the chemical most familiar to consumers as talcum powder. As carbon dioxide isn’t present in magnesium oxide no carbon dioxide is released. An additional carbon saving is achieved because Novacem only needs to heat the materials to about 800 degrees Celsius instead of 1450 degrees Celsius. Novacem claim that biomass could be used as a fuel to power the process instead of traditional fossil fuels. The process not only requires much less heating, it also absorbs large amounts of CO2 as it hardens, making it carbon negative.

Apparently, the processing of the ingredients for traditional cement releases 0.8 tonnes of carbon dioxide per tonne of cement. When it is eventually mixed with water for hardening each tonne of cement can absorb up to 0.4 tonnes of CO2, but that still leaves an overall carbon footprint of 0.4 tonnes of carbon dioxide per tonne of cement. The production of Novacem's cement creates a total of 0.5 tonnes of carbon dioxide per tonne of cement. But the Novacem cement formula absorbs far more carbon dioxide as it hardens - about 1.1 tonnes. So the overall carbon footprint is negative - i.e. the cement removes 0.6 tonnes of CO2 per tonne used. It is claimed that magnesium silicates are abundant worldwide, with 10,000 billion tonnes available.

Novacem are reported to be building a small-scale test plant to see if the concrete works and it hopes to have a larger-scale plant operating by 2011 and full-scale production underway by 2013.

Novacem was a finalist in the Carbon Trust’s Innovation Awards 2009.

See www.novacem.com and http://www2.technologyreview.com/article/418542/tr10-green-concrete/