Researchers Are Trying To Find A Solution To Cut Concrete's Carbon Emissions

Researchers are trying to make a cleaner concrete to cut greenhouse gas emissions and curb climate change. The industry is estimated to account for at least 7% of global carbon dioxide emissions.

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The most used substance on the planet is one you might expect - water. The second, though, might surprise you - it's concrete, the building material. Problem is, concrete production is a huge source of climate-warming carbon emissions. As NPR's Nathan Rott reports, researchers are trying to find a solution to the concrete problem.

NATHAN ROTT, BYLINE: Ah, the sounds of summer - that time of year when the roads are closed, the sidewalks blocked and the jackhammers sing.

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ROTT: Whether it's being busted or poured, concrete is key to all of it. Just look around. The roads we drive, the bridges we cross, the buildings we live and work in - all of it concrete. The world uses more than 10 billion tons of this stuff every year. It's the foundation of our modern society. And that presents a big problem, says engineer Gaurav Sant, because cement, the key ingredient in concrete, is a huge source of carbon dioxide, the chief driver of climate change.

GAURAV SANT: If you produce a pound of cement, you produce a pound of CO2, carbon dioxide.

ROTT: Sant is a professor of civil engineering and material science at the University of California, Los Angeles. He's sitting in a loud lab room at UCLA, and he says those numbers add up. The International Energy Agency estimates that cement production accounts for about 7% of the world's total CO2 emissions.

SANT: So it's a really big number.

ROTT: And one that is only expected to get bigger as the world's population grows.

SANT: Tackling it is actually what we need to continue society as we know it. So...

ROTT: So what to do? Well, it's hard to imagine the world's just going to stop using concrete. That's why Sant and his colleagues are out to make a new type of concrete altogether, making carbon dioxide part of their formula.

GABE FALZONE: First, the small version.

ROTT: Project scientist Gabe Falzone is part of Sant's team at UCLA. He opens a door into a room humming with lab equipment.

FALZONE: These are gas cylinders. That's a bottle of CO2.

ROTT: And yes, it's full. The cylinders of carbon dioxide are here to help simulate the type of emissions that come from making normal cement. Now, normal cement is made by super heating limestone. The limestone itself emits carbon dioxide during that process, and getting it to temperature usually means using a carbon-heavy heat source, something like coal. So that's a double whammy of CO2 emissions. What Falzone and his team have done is made a concrete-like substance that uses CO2 in its production. The carbon dioxide helps kick-start the hardening process.

FALZONE: So basically, in normal cement, that works by reaction of water; instead of that, it's the CO2 itself.

ROTT: This process, Falzone says, produces less than half of the carbon dioxide of normal concrete. Back in a quieter room, Gaurav Sant says the goal is to make cement production less carbon-intensive.

SANT: So if you want construction to continue to grow (ph), you need solutions to it that have a much lower carbon intensity.

ROTT: And their efforts are getting attention. Sant and his team are finalists for the Carbon XPRIZE, a global competition aimed at finding ways to convert CO2 emissions into valuable products. The goal is to make this greener concrete economically competitive with its traditional counterpart. As the world looks to cut carbon emissions from our cars and our power plants, Sant says, it's vital to also look at reducing the carbon footprint of heavy industry.

SANT: So all of the things that we're used to - right? - petrochemicals, concrete, cement, steel, glass - these are the sectors that are actually very hard to decarbonize because running them off renewable energy is not a trivial undertaking.

ROTT: But, Sant says, it's one that the world must undertake if we want any chance of stemming global warming.

Nathan Rott, NPR News, Los Angeles.

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