The Carbon in Concrete

Scientists estimate that concrete accounts for about 5% of the world’s carbon footprint.

Concrete, the most widely used building material in the world, releases carbon dioxide (CO2) as it is produced and again during transportation and construction. Scientists estimate that concrete accounts for about 5% of the world’s carbon footprint. But concrete has a secret—the ability to reabsorb CO2. Carbon dioxide in the air combines with components in the concrete to form the solid substance calcium carbonate.

Researchers speculate that this ability may lead to lower carbon-footprint construction, perhaps even carbon-neutral materials. Liv Haselbach, a civil and environmental engineering professor at Washington State University, published a study in the June 2009 Journal of Environmental Engineering on this special property of concrete.

Haselbach is looking closely at cement processing, a precursor to concrete, in order to fully understand concrete’s ability to absorb CO2. "People haven’t gone back yet and seen the form before it turns into limestone," she says. "I was interested in other things in there besides calcium carbonate."

She is looking for other components in concrete that may absorb CO2, a critical step to quantifying its carbon footprint. Understanding concrete’s true environmental impact is essential to making smart decisions about its future use, she says. "If we know what’s in there we might be able to accelerate carbon dioxide absorbing," she says. "If we can facilitate it coming back in, we can make it more carbon neutral."

Even though Haselbach studies concrete at a molecular level, she is interested in the big picture—investigating how much CO2 is burned in the kiln, released during transportation, even given off while the truck mixer is turning.

While this research is still in the early stages, Haselbach is optimistic about its potential. "Preliminary research showed we really have to look at the whole picture," she says.

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