A new study from University or California Irvine shows that cement is a net carbon dioxide sink.
Cement manufacturing is among the most carbon-intensive industrial processes, but an international team of researchers has found that over time, the widely used building material reabsorbs much of the CO2 emitted when it was made.
“It sounds counterintuitive, but it’s true,” said Steven Davis, associate professor of Earth system science at the University of California, Irvine. “The cement poured around the world since 1930 has taken up a substantial portion of the CO2 released when it was initially produced.”
Cement manufacturing is considered doubly carbon-intensive because emissions come from two sources. CO2 molecules are released into the air when limestone (calcium carbonate) is converted to lime (calcium oxide), the key ingredient in cement. And to generate the heat necessary to break up limestone, factories also burn large quantities of natural gas, coal and other fossil fuels.
Davis and his fellow researchers looked at the problem from a different angle. They investigated how much of the gas is removed from the environment over time by buildings, roads and other kinds of infrastructure. Through a process called carbonation, CO2 is drawn into the pores of cement-based materials, such as concrete and mortar. This starts at the surface and moves progressively inward, pulling in more and more carbon dioxide as years pass.