Innovative new concrete absorbs carbon emissions

Traditional (or Portland) cement is made by heating limestone and clay in giant kilns to around 1,500°C. The vast amounts of energy needed to heat the raw materials, along with the chemical reactions as the limestone decomposes, produces a hefty 0.83 tonnes of CO2 for every tonne of cement, according to the International Energy Agency. When it’s mixed with water for use in building, each tonne absorbs up to 0.4 tonnes of CO2. But that still leaves net carbon emissions of over 0.4 tonnes CO2 for each tonne of cement in use.

Now Novacem (a spin-off company from London’s Imperial College) is developing a cement based on magnesium oxide, derived from mineral silicates. This material requires heating at the much lower temperature of 650°C, and emits less than 0.5 tonnes of CO2 per tonne of cement produced. But crucially, it has the potential to absorb large amounts of CO2 as it hardens.

The Novacem team are now working with WSP Group, Laing O’Rourke and Rio Tinto Minerals to assess the material’s feasibility, and test its efficacy. If tests prove its suitability for large-scale construction projects, they expect it to be on the market within five years.

MPA Cement (formerly the British Cement Association) believes this timeline could be overly optimistic. Senior Standards Manager Mike Taylor points out that it may be hard to find enough magnesium silicate minerals to manufacture the cement on a commercial scale in the UK – although the minerals are abundant worldwide. Transporting them to manufacturing sites will have a significant environmental impact, he warns.

But it’s the cement’s performance as a construction material that will be key to its success. Unless it is able to replace the Portland variety on a large scale, says Taylor, it won’t have a significant impact on climate change. – Giovanna Dunmall

16 April 2009