Headquartered in Somerville, Mass., just north of Boston, Sublime Systems is working to remove carbon emissions from the concrete-making process. In addition to water, sand, and aggregate, traditional concrete mixes require Portland cement, an expensive and energy-­intensive product projected to reach 5.8 billion tons in global CO2e emissions by 2027. Nearly half of those emissions come from burning coal and other fossil fuels to heat a kiln up to 1500°C, and the other half from the chemical decomposition of limestone inside the kiln.

Sublime Systems cancels out both emissions sources. The process starts with calcium silicates, or noncarbonate feedstocks made from abundant rocks and minerals, as well as recycled industrial waste like fly ash and blast-furnace slag. Unlike limestone, there is no CO2 bonded to these materials, yet they still contain the key ingredients needed to make cement. Sublime’s electrolyzer (electrochemical reactor) burns no fossil fuels and requires temperatures only up to 100°C to achieve the necessary chemical reaction. An independent life-cycle assessment also confirmed that this process eliminates more than 90% of the global warming potential compared to Portland cement.

Sublime currently has a pilot electrochemical cement manufacturing facility capable of producing 250 metric tons of cement per year, but is in the process of developing a commercial plant in Holyoke, Mass., capable of producing a low-carbon cement by the kiloton. The plant itself will occupy a series of former paper mills and run on the river’s hydropower, which the company has cited as critical infrastructure for its fully electrified manufacturing process. Earlier this year, Sublime was awarded $87 million from the U.S. Department of Energy to ramp up production and create training programs for local labor. This is all coming soon—the Holyoke facility is expected to come online in 2026.

— Justin Wolf; Maine-based writer who covers energy and climate policy and green building trends

From Fine Homebuilding #324

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• • Taking the Environmental Sting Out of Concrete
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  • A Better Path to a Low-Carbon Future?
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