Tossing out the thermal heat
Sublime Systems isn’t just searching for lower-carbon ingredients. The Boston-based startup is developing an entirely different way of driving chemical reactions that turn minerals into cement — one that doesn’t involve any fossil-fuel-burning, high-temperature kilns.
Sublime, which spun out of MIT in 2020, uses an electrochemical process instead of thermal heat. At the heart of its approach is an electrolyzer, which splits water to produce an acid and a base. A range of carbon-free rocks, minerals and industrial waste materials can be dissolved in the acid to extract calcium. The calcium is then reacted with the base, a step that creates calcium hydroxide, or lime.
Finally, the company blends the lime with silica — just as the ancient Romans once did — to produce what it calls “Sublime cement.” Once mixed with water, the cement hardens by forming “calcium silicate hydrate,” the same product that Portland cement makes. The entire process takes place at ambient temperatures; by replacing limestone inputs with alternative materials, Sublime says it can further reduce the emissions that typically occur when limestone decomposes in fiery-hot kilns.
“That’s how we avoid the kiln entirely: by using electricity,” Leah Ellis, Sublime’s CEO, told Canary Media. Ellis and her co-founder Yet-Ming Chiang, a renowned material sciences professor at MIT, both focused on batteries before pivoting to low-carbon cement.
The company completed its first pilot plant in late 2022, which can produce as much as 100 metric tons of cement per year. It’s also pursuing plans for a first commercial facility that can produce tens of thousands of tons of cement per year. In September, Sublime obtained a key industry designation that says its product meets certain performance-based standards for hydraulic cement.
“It’s a first-of-a-kind technology that we have to scale up, and that’s going to be hard,” Ellis said. “You have to get to a certain size before you’re even real to the cement or the concrete industry.”
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