‘Concrete jungle’ is surprisingly green – study

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DESPITE being one of the biggest sources of manmade carbon dioxide emissions, concrete is a surprisingly effective carbon sink, removing an amount of carbon dioxide from the atmosphere equal to nearly half that produced in concrete manufacturing, researchers said in findings published in Nature Geoscience.

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Production of concrete accounts for as much as five percent of global carbon dioxide emissions annually, and is considered particularly carbon-intensive because carbon dioxide is produced through combustion of fuel in the manufacturing process as well as calcinations, the chemical reaction that converts carbonate rock into cement.

The research team led by Xi Fengmeng, an associate professor at the Institute of Applied Ecology of the Chinese Academy of Sciences investigated the impact of carbonation, the reverse process of calcination, which naturally occurs over time. As carbon dioxide diffuses into the pores of cement, it reacts with calcium oxide through a process called carbonation.

Xi and his team created an analytical model of carbonation based on data about concrete production, service life, and secondary use between 1930 and 2013 to estimate regional and global carbon dioxide uptake over that time period.

According to the study, more than 76 billion tons of cement were produced around the world from 1930 to 2013 with four billion tons produced in 2013 alone.

The researchers found that carbonation of cement materials over their life cycle represents a large and growing net sink of carbon dioxide, increasing from 0.10 gigatons of carbon per year (GtC/y) in 1998 to 0.25 GtC/y in 2013.

The study estimated that a total of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43 percent of the carbon dioxide emissions from the production of cement over the same period.

“The global carbon uptake by cement carbonation is large and substantial, which give a new perspective for the ‘missing sink mystery’,” Xi said in the report, referring to a puzzling gap in carbon sequestration data that indicates some unknown mechanism removes some carbon dioxide from the atmosphere.

“The carbon sink from human activities has not yet been revealed comprehensively,” Xi added. “New technologies for carbon capture and storage using cement wastes should be developed for climate change mitigation.”

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