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Concrete is the world's most widely used building material on every continent on the planet.. But the production of concrete generates tonnes of CO2 emissions every year, around 2.8 billion tonnes - only the USA and China as entire countries emit more carbon than that. Dr Natasha Boulding, co-founder of the Low Carbon Materials company, has been working to try to make its production more environmentally-friendly. She told Newshour's Rebecca Kesby more about the process. (Photo shows concrete steps in the City of London. Credit: Laurence Coss/Â鶹Éç)