Concrete contributes about eight percent of the world’s carbon footprint – around 3 billion tonnes of carbon dioxide – but research into a new type of concrete that actually traps carbon could cut its emissions drastically.
“My dream goal for the future would be to close the cycle so we have zero emission concrete,” says Dr Anna Herring, a researcher at ANU Research School of Physics.
Dr Herring is studying concrete that’s formed with magnesium, instead of calcium.
Conventional concrete is formed from the raw material limestone (calcium carbonate CaCO3). During the processing, limestone is converted to calcium oxide (CaO), releasing carbon dioxide.
Magnesium-based concrete undergoes a similar chemical process, but is able to re-trap the carbon dioxide within the crystalline structure of the magnesium-based minerals, by forming hydrated magnesium carbonates [for example, nesquehonite, Mg(HCO3)(OH)•2(H2O)] which form the binding material that holds the concrete together.
Trapping carbon dioxide in this way would cut as much as 70 percent of the emissions from concrete.
The bulk of the remaining carbon footprint comes from fuel burnt to heat the raw materials used to form the cement – the creation of conventional calcium-based concrete requires temperatures of around 1500 degrees Celsius.
Magnesium-based concrete scores well in this area too, needing to be heated to only 800 degrees Celsius, making the carbon footprint from its heating smaller than for conventional concrete.
“And if that were driven by a sustainable energy source, such as solar thermal, we could get close to zero emissions,” says Dr Herring.
“I hope we can support the construction industry around the world to move towards zero emissions.”