Low-carbon concrete is at a tipping point

When workers repaved part of Interstate 94 near Minneapolis last fall, it looked like they were pouring ordinary concrete. But instead the highway was the first to use a new, near-zero-emissions material.

It’s one of a series of large projects to use material from C-Crete, a Bay Area-based startup. Shortly, the highway was repaved, and the company poured slabs and foundations at San Francisco International Airport. Earlier in the summer, it also poured a floor slab in a super-tall skyscraper under construction in Manhattan, the future headquarters of JPMorgan Chase. Other projects are underway now.

[Photo: courtesy C-Crete Technologies]

Producing cement, the glue that holds concrete together, is a major source of global emissions—around 8% to 9%, or three times as much as the aviation industry. But as startups are racing to bring low-emissions alternatives to market, some of those new products may be at a tipping point.

“This is cost-competitive,” says C-Crete CEO Rouzbeh Savary, who began working on a more sustainable cement alternative as a PhD student at MIT. “We’re making binders that are the same cost, same performance, and no CO2.”

Typical Portland cement, which has been in use for the past 200 years, is a big polluter for two reasons. First, it’s made by heating up limestone, which releases CO2 as the limestone breaks down. The process also uses a lot of energy, which is usually run on coal and other fossil fuels.

JPMorgan, 270 Park Ave. [Photo: courtesy C-Crete Technologies]

C-Crete replaces limestone with other rocks that don’t contain CO2, such as granite or zeolite. Some other startups are taking a similar approach. Brimstone, for example, a startup backed by Bill Gates’s Breakthrough Energy Ventures, uses calcium instead of limestone. Sublime Systems, another startup, dissolves calcium silicate with chemicals. (Sublime first poured concrete for a building in Boston a year ago, and won a DOE award in December to build a new, clean-cement factory in Massachusetts.) C-Crete says that it has a simpler process: Rather than extracting a single element from rocks, requiring multiple steps and creating waste, it found a way to use the full mix of materials inside granite and other rocks.

The team spent years developing a process that worked. “We had thousands of failed formulas, so this didn’t come overnight,” Savary says. In the final process, rocks are pulverized, and then the company adds a mix of chemicals—calibrated for a particular rock’s composition—to reform a new, strong material.

The process uses far less energy than making Portland cement; if it’s made renewable energy, the binder can be zero-emissions. (The other materials in concrete, like sand and water, are only a minor source of emissions.) The poured concrete also acts like a sponge, capturing CO2 from the air as it cures.

[Photo: courtesy C-Crete Technologies]

When the binder is used to make concrete, the material is as durable and strong as conventional concrete, the company says, meeting ASTM performance standards. It also flows and pumps like typical concrete, so construction methods don’t have to change.

In its initial projects, C-Crete now produces cement itself. But the startup is now in discussions with ready-mix concrete companies around the country that can use its approach. Those companies already have quarries where they mine rocks like granite for aggregate. They can buy off-the-shelf equipment to pulverize the rocks, and then use binder materials from C-Crete; the changes can easily integrate into the existing construction industry without needing large-scale investments in manufacturing.

San Francisco International Airport [Photo: courtesy C-Crete Technologies]

Unsurprisingly, the construction industry is cautious about adopting new materials. But as a growing number of real-world projects demonstrate the performance of the concrete, it could scale up quickly. Some building owners might choose the material for sustainability reasons, but the biggest factor in its favor will likely be the affordability. While the material already competes on cost, it has the potential to become even cheaper than conventional concrete, since it’s more efficient to produce.

“We believe that what we are doing is the most scalable, simplest, and most affordable way of decarbonizing concrete,” says Savary.

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