This article is part of our special series "The Tough Stuff: Decarbonizing steel, cement and chemicals." Read more.

Video: See how this NYC factory traps CO2 in concrete blocks

Canary Media visits a Brooklyn warehouse and the basement of a Manhattan high-rise to learn how CO2 can be captured and turned into construction material.
By Maria Gallucci

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A rectangular gray concrete block on a factory conveyer belt. A U.S. flag draped on equipment is seen in the background.
Concrete blocks roll down the line at Glenwood Mason Supply in Brooklyn, New York. (Stephanie Primavera/Canary Media)

BROOKLYN, New York — Jeff Hansen climbs up onto a narrow metal platform and stands beside three towering mixers, which are stirring up concrete with the texture of wet sand. In the bustling warehouse below, tall machines press the concrete into molds like giant Play-Doh sets, churning out thousands of building blocks per day at the Glenwood Mason Supply facility in East Flatbush, Brooklyn.

To make the concrete in these jumbo mixers, Glenwood Mason dumps in Portland cement, sand, crushed aggregates and one final key ingredient: carbon dioxide.

Using a novel technique, the company takes planet-warming CO2 and renders it into dry ice, as Hansen explains over the deafening noise of hissing, clanking machinery. When that dry ice is mixed with the cement, a chemical reaction occurs, transforming CO2 into calcium carbonate. In its mineral form, the carbon won’t escape back into the atmosphere.

It’s in the blocks forever,” Hansen, the firm’s vice president of architectural sales and marketing, says on a toasty October afternoon.

Injecting CO2 into concrete is one of many approaches that companies are taking to address the construction industry’s outsize climate impact. Cement and concrete production are responsible for roughly 8 percent of total human-caused CO2 emissions every year, more than the aviation and cargo-shipping sectors combined.

The majority of concrete-related emissions come from making Portland cement — the glue that binds other ingredients together. A growing number of startups and manufacturers worldwide are developing low-carbon formulas and new techniques to prevent those emissions from being created in the first place.

The Brooklyn project takes a different tack. Instead of directly reducing emissions, it uses the blocks to lock away CO2 pollution that otherwise would have escaped into the air. This helps to compensate for the carbon emissions released in the production process. All told, this method can curb the overall carbon footprint of concrete by roughly 5 percent, according to the company CarbonCure, which developed the CO2-injection technology that Glenwood Mason uses.

A large delivery truck with the words Sustainable CO2 on the back stops in front of an industrial facility
A truck delivers CarbonQuest's captured CO2 to Brooklyn, New York. (CarbonQuest)

To get the CO2 for its blocks, Glenwood Mason is tapping an unusual source: a high-rise apartment building in Manhattan.

Earlier that morning, some 16 miles away and many feet below ground, Brian Asparro stood between two pale-green boilers, their tiny windows aglow from the orange flames flickering inside. The units burn fossil gas to supply heat and hot water to the 350,000-square-foot property at 1930 Broadway Avenue.

Asparro is the chief operating officer of CarbonQuest, a startup that’s developed a way to capture CO2 emissions from fossil-fired heating systems. Around the corner, a labyrinth of pipes, filters and condensers siphon carbon dioxide from the boilers’ flue lines and turn it into liquid.

CarbonQuest launched four years ago to help New York property owners comply with the city’s stringent climate policies. Starting next year, Local Law 97 will require most buildings over 25,000 square feet to meet certain energy-efficiency and emissions targets, with even stricter limits taking effect in 2030.

In many cities, especially cold-weather cities, natural gas is so ingrained in the infrastructure,” Asparro said. How do you quickly, cost-effectively — and without a major disruption — reduce emissions [from buildings] while the grid starts to green?”

CarbonQuest launched its first carbon-capture system in the Broadway building a year and a half ago. The company is now installing and operating five units in other rental properties across the city. He said CarbonQuest hopes to expand its technology into other cities and states where building owners are being required to slash CO2 emissions, including Boston, Colorado and Washington state. Eventually, the CO2 that CarbonQuest captures could be used in myriad ways, such as replacing petroleum in chemical and jet-fuel production.

In the meantime, CarbonQuest will continue trucking its liquified CO2 across the East River to Glenwood Mason’s facility in eastern Brooklyn.

Back at the warehouse, the CO2-infused blocks roll down conveyor belts and onto tall racks, which move autonomously into one of two cavernous kilns. At 135 degrees Fahrenheit and 100 percent humidity, standing inside a kiln feels like visiting a dusty, gritty sauna.

Hansen says property developers are increasingly asking building-material suppliers to disclose the climate impacts associated with making their products. In addition to using CO2 during manufacturing, Glenwood Mason has taken other measures to reduce its overall emissions, including by installing solar panels on its property. Adding recycled glass and supplementary cementing materials to its concrete mix helps reduce the total amount of carbon-intensive cement used in each block.

Then we send that block into the city [for new construction], to create that circular economy,” he adds.

Maria Gallucci is a senior reporter at Canary Media. She covers emerging clean energy technologies and efforts to electrify transportation and decarbonize heavy industry.