Cutting concrete’s carbon footprint

Emitting up to five percent of man-made carbon dioxide on earth, the cement industry is the second largest greenhouse gas emitter worldwide behind power generation. So it stands to reason that finding a more sustainable alternative to standard concrete, which typically contains 10 to 15 percent cement, could have far reaching impacts.

A groundbreaking company based in Halifax, Canada has done just that. CarbonCure Technologies has developed a proprietary technology that allows concrete manufacturers to produce a concrete that sequesters waste carbon dioxide during the manufacturing process to reduce emissions by about 10 to 15 percent on average.

Let that sink in for a second: a concrete that captures carbon dioxide.

“Nobody does what we do in terms of reintroducing CO2 into concrete,” CarbonCure Director of Corporate Development Rachel Aaron told us, “but also what we do works with what [manufacturers] already do and nobody else is going that way.”

CarbonCure performs this magic trick by injecting post-industrial CO2 into concrete during the mixing of the cement, water, and aggregate, where it is chemically converted into a limestone-like mineral, effectively sequestering the CO2. After being injected into the concrete as a liquid, the CO2 converts into gas and ultimately into a solid that won’t release into the atmosphere even if it is demolished and dumped into a landfill. The company says the product can be stronger than conventional concrete, and those who use it can also receive LEED credits – a true win-win.

FAST FACT: 4 billion tons of cement are produced every year.

“Nobody wants to stop building with concrete they just wish it wasn’t so bad,” Aaron said. “So definitely this way to make it is better. With [building] owners it can be eye opening.”

Suffolk Construction recently tested CarbonCure for potential use on several upcoming Southeast projects, including All Aboard Florida and the Miami Worldcenter. The trials at Titan American’s Pennsuco cement plant in Medley, Fla. involved testing varying amounts of CO2 sequestered in six trucks worth of mixed concrete.

The results found that the CarbonCure batches are approximately seven percent stronger than the control batch of traditionally mixed concrete at the end of the 28-day compressive strength test. Also, the CarbonCure batch had a higher “early strength,” which means crews could potentially finish concrete floors faster or use less cement to obtain the same strength.

“At the end of the day if you can prove its the same product at the same cost and here’s what it does in addition to the stuff you normally use, that’s a big deal,” Suffolk Construction’s Green Team Southeast Captain Mike Joslyn told us. “Certainly it’s a worthwhile option.”

But more exciting than the results of those tests is that Joslyn’s team tested CarbonCure for poured products such as ready-mix concrete, which has potential to sequester even greater amounts of CO2 on large-scale building projects. Up until last year CarbonCure mostly had been used for masonry blocks since they are made on a controlled assembly line that can easily regulate the amount of CO2 pumped into each block.

Using CarbonCure to make ready-mix is much harder to control because it’s mixed in a truck and the CO2 has to be introduced properly. Aaron said optimizing the strength of the concrete depends not only on the CO2 in each batch but also on precisely timing the introduction of CO2 to the mixture.

CarbonCure successfully achieved this feat for the first time in a commercial trial last summer for a 40-story condominium project in Toronto.

“Oh yeah it was thrilling,” Aaron said. “It was amazing to see how it all worked out. We were excited to see how well it went.”

Now that they have optimized concrete at more and more factories in the United States and Canada, Aaron said CarbonCure is attracting more and more interest across North America.

She also said CarbonCure is focusing on the Southeast and South regions since more ready-mix is poured in that market than anywhere else in Canada and the United Sates.

“Certainly this is something we will roll out nationally,” she said. “It’s just a matter of time and where we want to focus our efforts on first.”

Josh Rollins and Mike Joslyn collaborated on this story. If you have questions, Josh Rollins can be reached at jrollins@suffolk.com or follow him on Twitter @joshkrollins. Mike Joslyn can be reached at mjoslyn@suffolk.com or follow him on Twitter @MikeBJoslyn.

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