Climate corrective or another Theranos?

I have fond feelings toward concrete. The years of life I spent pouring and shaping the stuff while doing earthquake safety retrofits left me appreciating that this is a fluid, malleable, lively substance, not just inert rock.

And so I'm emotionally inclined to imagine that a purported breakthrough in turning concrete construction into a carbon reducing tool might be more than hype. According to something called the Foundation for Climate Restoration offered as sponsored copy in Grist, a Los Gatos entrepreneur named Brent Constantz has launched a company that makes synthetic limestone using carbon captured from our polluted air. The result can be used to make carbon neutral concrete.

Blue Planet’s process starts with collecting CO2 and dissolving it in a solution. In the process, the company creates carbonate that reacts with calcium from waste materials or rock to create calcium carbonate. Calcium carbonate happens to be the main ingredient in limestone. But rather than superheating it to create cement (which would release all that CO2 right back into the atmosphere), Constantz and his team turn the resulting stone into pebbles that serve as aggregate.

This is easiest to do where there’s lots of CO2 — smokestacks at factories, refineries and power plants, for example — but it can also come from “direct air capture,” using less concentrated air anywhere, a technology whose costs are rapidly declining.

Do this on a large scale, Constantz said, and you could help satiate the growing global demand for rock and sand, and make a massive dent in the climate crisis at the same time: Every ton of Blue Planet’s synthetic limestone contains 440 kilograms of CO2. While it still needs to be mixed with cement (the goopy stuff) to make concrete, using this in place of gravel or stone that needs to be quarried and crushed creates a finished product that is carbon neutral, if not carbon-negative, according to the company.

Well maybe. A less credulous article in the Journal of the American Institute of Architects surveys a range of efforts along these lines. While insisting that further study is needed, fast, these architects find the prospect of incorporating negative emission technologies in their buildings enticing:

In the coming years, buildings may share the burden of achieving negative carbon emissions—attending to client needs as well as global imperatives. Exactly how they can meet this challenge represents both a significant test and a grand opportunity for architecture.