Sequestering CO2 emissions in concrete

Winning UCLA team tested idea at Wyoming facility near Gillette

by Allen Best

Big Pivots

Winners of the Carbon XPrize announced last week both propose ways to use carbon dioxide emissions in concrete.

One contest winner focused on coal, and the other on emissions from natural gas. Each won $7.5 million in the contest that was launched in 2015.

CarbonBuilt, a team from the University of California Los Angeles, won the coal contest after testing the technology at Wyoming’s Integrated Test Center. The test center, part of the Dry Fork Station coal plant near Gillette, was launched in 2015 with $15 million in funding, including $5 million from Tri-State Generation and Transmission.

The UCLA team figured out a way to take carbon dioxide emissions directly from a coal-burning power plant and infusing them into a new type of cement invented by the team. As the concrete hardens and gains strength, it permanently absorbs and traps the greenhouse gas.

Each concrete block stores three-quarters of a pound of carbon dioxide. A press release from UCLA notes that an estimated 1 trillion concrete blocks will be produced annually by 2027.

Gaurav Sant, a professor of civil and environmental engineering at UCLA, explained that the original inspiration for this idea came from seashells.

“Sea shells are made of calcium carbonate, which is nature’s original cementation agent,” he said. “We were really motivated by the idea of how seashells were held together. And that’s how we really set about to turn carbon dioxide into concrete.”

The UCLA researchers developed a new formula for cement, the binding agent in concrete. They used hydrated lime, or portlandlite, which can absorb carbon dioxide quickly, to replace traditional calcium silicate cement, known as ordinary Portland cement. Then the team created a method in which carbon dioxide taken directly from the flue gas of the power plant is quickly absorbed by portlandlite as the concrete hardens.

There’s a bonus to this method, says the UCLA team. The process reduces the amount of ordinary Portland cement needed to produce concrete by between 60% to 90%. The process also occurs at ordinary temperatures and pressures. This reduces the carbon footprint of the concrete. Traditional cement used in concrete causes nearly 9% of the world’s carbon dioxide emissions.

This is from the April 30, 2021, issue of Big Pivots, an e-journal covering the energy and water transitions in Colorado and beyond. Sign up at Big Pivots.com.

In the press releases and other public statements, however, there was no mention of just how much of a dent this process could make in emissions from coal combustion even if all concrete bricks worldwide were made using this process.

Here’s the beginning of the math: each brick can absorb three-quarters of a pound of C02. The Energy Information Administration reported that in 2019 each kilowatt-hour of electricity produced by coal combustion was responsible for 2.19 pounds of CO2. And 1,949 million short tons of C02 were produced.

Will coal really be needed? An essay in the May/June issue of Foreign Affairs points to China’s continued expansion of coal-burning unit. The essay by Andrew S. Erickson and Gabriel Collins says this: “China’s net coal-fired power generation capacity grew by about 30 gigawatts over the course of the year, as opposed to a net decline of 17 gigawatts elsewhere in the world. China also has nearly 200 gigawatts’ worth of coal power projects under construction, approved for construction, or seeking permits, a sum that on its own could power all of Germany—the world’s fourth-largest industrial economy. Given that coal power plants often operate for 40 years or more, these ongoing investments suggest the strong possibility that China will remain reliant on coal for decades to come.”

As for the natural gas prize, it was won by CarbonCure Technology working out of the Alberta Conversion Technology Centre in Alberta. CarbonCure demonstrated a technology that enabled production of concrete with a reduced water and carbon footprint. A precise dose of CO2 is injected into a concrete plant’s reclaimer system, which contains the water used to wash out concrete trucks and mixers. The CO2 is converted to a permanently embedded mineral with strength-enhancing properties, which can then be incorporated into new concrete mixes.

Top photo: Gaurav Sant, professor of civil and environmental engineering and of materials science in the UCLA Samueli School of Engineering. Photo/UCLA

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