Of all the so-called “difficult to decarbonize” sectors, cement is among the most vexing. Making cement produces CO2 not merely through fuel combustion (in kilns that reach temperatures of up to 1400 C), but also through chemical processes that split CO2 off from other molecules. It is responsible for roughly 8 percent of total global carbon emissions.

Most gestures at decarbonizing cement to date are fairly desultory — things like adding special additives or injecting a little CO2 when the cement is mixed into concrete. The only widely available method that could theoretically produce no- or low-carbon cement is post-combustion carbon capture and sequestration. And there are plenty of people who would question whether that’s actually viable at all, much less widely available, given that it would roughly double operational costs for a cement plant.

There are lots of startups out there attempting to solve this problem (as reported by Canary last month). Perhaps the most intriguing is Sublime Systems, a team that has developed something truly new and exciting: a system for manufacturing cement that requires no high heat (thus no combustion emissions) and uses inputs that contain no carbon (thus no chemical emissions). That makes the cement, at least potentially, not just low-carbon but zero-carbon. What’s more, the company says that, in form and performance, its product is a perfect drop-in substitute for traditional Portland cement, so it wouldn’t even require any changes in the construction industry.

A carbon-free drop-in cement substitute — at scale and at competitive cost — would be genuinely transformative. I contacted Sublime CEO Leah Ellis to talk about cement chemistry, the company’s process, and the plan for reaching megaton scale. This one was truly fascinating and educational for me; I think you will really like it.