Study: Cement Absorbs Greenhouse Gas
For years, concrete—specifically the Portland cement that comprises much of the material—has gotten a bad rap in terms of carbon emissions. But new research indicates that even as the production of cement is creating carbon dioxide, the cement itself may eventually absorb nearly as much CO2 from the atmosphere.
The new study comes via the University of California, Irvine, where physicist Zhu Liu and Steven Davis, an associate professor of Earth system science, have been working with an international, multi-institution team of scientists to study carbon emissions and cement. The team’s main finding: Cement seems to actually act as a “carbon sink,” absorbing CO2 so it cannot contribute to the greenhouse effect.
“It sounds counterintuitive, but it’s true,” Davis said. “The cement poured around the world since 1930 has taken up a substantial portion of the CO2 released when it was initially produced.”
Taking in CO2
It happens through a process called carbonation: Cement materials like concrete and mortar actually absorb CO2 through their pores, removing the gas from the air and preventing it from trapping heat within Earth’s atmosphere.
The researchers aren’t saying a concrete cityscape is just as good as a forest for bringing down carbon in the atmosphere—cement production is still responsible for a net increase in CO2. But perhaps it’s not quite the heavy polluter some had previously thought.
Production and Absorption
According to the study, cement production released 38.2 gigatons of CO2 into Earth’s atmosphere during the period between 1930 and 2013, both from limestone conversion and from fossil fuels burned in the production process. But the researchers estimate that cement absorbed 4.5 gigatons of CO2 through carbonation during that same period.
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Cement production releases CO2 into the atmosphere both as a direct result of limestone conversion and from fossil fuels burned in the production process.
That’s nearly 12 percent of all CO2 produced during cement production—and, the study notes, it’s about 43 percent of the CO2 created by limestone conversion, which is a necessary step in cement production. The conclusion it all points to: It’s fossil fuels, not cement production itself, that contribute most heavily to CO2 emissions and the resulting climate effects.
“Cement has gotten a lot of attention for its sizable contribution to global climate change, but this research reinforces that the leading culprit continues to be fossil fuel burning,” Davis said.
The study, titled “Substantial Global Carbon Uptake by Cement Carbonation,” was published last month online by Nature Geoscience. In addition to Davis, it was authored by 18 other scientists representing a total of 17 institutions in China, Denmark, France, South Korea, Spain, the U.K. and the United States.