Environment
A process that uses waste from demolished buildings could cut the climate impact of construction
CEMENT can now be made using the waste from demolished buildings, which researchers say could save billions of tonnes of carbon by 2050.
“We have definitely proved that cement can be recycled into cement,” says Julian Allwood at the University of Cambridge. “We are on course for making cement with zero emissions, which is amazing.”
The production of cement is responsible for 7.5 per cent of total greenhouse gas emissions, but until now there was no known way to make it on a big scale without affecting the climate.
Creating cement requires “clinker”, which is made by heating a mix of raw materials, including limestone and clay, to 1450°C. Both the heat requirements and the chemical reactions involved in making clinker result in carbon emissions, and clinker production accounts for 90 per cent of cement’s total carbon footprint.
Allwood and his colleagues have now developed a way to make clinker by reusing cement paste made from demolished buildings. This paste has the same chemical composition as lime flux, a substance used to remove impurities from recycled steel. As the steel melts, the flux made from old cement forms a slag that floats on the top of the recycled steel. Once ground into a powder, the slag is identical to clinker. It can then be used to make Portland cement, the most common form of cement.
If the recycled steel and cement are produced using an electric furnace, powered by renewable or nuclear energy, the process is almost entirely free of emissions. “The idea is really simple,” says Allwood.
Lab trials have shown that the process works. It offers a “drop-in” solution that could be used with conventional equipment, and a global switch to this process could save up to 3 gigatonnes of carbon dioxide a
