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    New research finds cement-products to be a ‘substantial carbon sink’... but is it just greenwash?

    Nathan Johnson

    A new study published in Nature Geoscience reports that the carbon footprint of cement production could be being overestimated.

    The research, conducted by a team led by Harvard University physicist Dr Zhu Liu, attempts to quantify the amount of carbon dioxide (CO2) cement products absorb from the atmosphere in a process called carbonation.  

    According to the study, 43 per cent of carbon emissions released during cement production between 1930 and 2013 have been offset by the process of ‘carbonation’, wherein cement products absorb carbon dioxide from the atmosphere.

    The team used new and existing data on cement characteristics to mathematically model the amount of CO2 sequestered globally by four different cement materials — concrete, mortar, construction cement waste and cement kiln waste —during service life, demolition and secondary use.

    Describing cement as a ‘substantial carbon sink’, the researchers estimated that 4.5 gigatons of carbon were sequestered between 1930 and 2013, equivalent to 43 per cent of the CO2 emitted from calcination during that period.

    The researchers suggest that future emissions inventories and carbon budgets may be improved by including this ‘carbon sink’.

    GOOD NEWS OR GREENWASH?

    Although carbonation may offset the process CO2 of cement it can also lead to the corrosion of steel in concrete and its premature failure, thus reducing the lifecycle of the cement used. It can also cause the need for further cement production if the failing concrete needs to be replaced.

    Similarly, process CO2, or calcination, is only a portion of the total CO2 produced by cement production and the report’s 43 per cent sequestration figure doesn’t account for this.

    Fossil fuels used in the production of cement were also not included.

    It also doesn’t take into account the emissions from steel and aggregate production and both are essential parts of concrete buildings.

    While cement will never match up to the carbon sequestering benefits of wood, the study does establish that concrete buildings may not be as environmentally unfriendly as previously believed.

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