Fast Forward: In defence of concrete

Words: Rima Sabina Aouf

Concrete has an image problem. In the last few years, it’s become common to read that this everyday building material makes an outsized contribution to climate change, accounting for as much as eight percent of all the world’s carbon dioxide emissions. If it were a country, concrete would be the third largest emitter on the planet, after the USA and China. The reason for this high figure is because making concrete doesn’t just require massive amounts of energy or fuel; the production of its main ingredient, cement, also involves a chemical reaction that lets loose carbon dioxide as a by-product. In elemental terms, cement requires calcium oxide (CaO), but what’s naturally available in the world is limestone (CaCO3). To get from one to the other, you need to subtract CO2.

The visibility of this problem has made it a focus for engineers and scientists, who are in a race to bring a zero- or even negative-carbon concrete to the market. Some of their ideas boggle the mind. Researchers at the University of Colorado Boulder have succeeded in making cement from limestone that is grown by algae rather than mined from quarries. Like trees, algae draws down carbon dioxide from the atmosphere as it grows, so the product would be carbon neutral, releasing only the same amount of the gas back into the air when it is burned to make cement.