We are closing in on zero-carbon cement

The cement industry, responsible for roughly 8 percent of total global carbon emissions, is notoriously difficult to decarbonize. But a new startup, Sublime Systems, aims to manufacture zero-carbon cement that can easily be substituted for the traditional version. In this episode, Sublime CEO Leah Ellis talks through the company’s vision and process.

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David Roberts:

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.

All right then. Leah Ellis, CEO of Sublime Systems, welcome to Volts. Thank you so much for coming.

Leah Ellis

Thank you so much for having me.

David Roberts

I'm excited today to talk about concrete, everybody's favorite subject. But first I wanted to ask you, I know you and your partner originally were trained as and educated as battery scientists. I'm just curious how you ended up here. What drew you into this area, this problem?

Leah Ellis

Yeah, my co-founder is a professor at MIT, Yet-Ming Chiang, and he's in the material science department, and I'm a chemist by training. I like to think of chemistry as the central science that combines everything from physics to biology. All of the good stuff you can sort of spread into anything from a foundation in chemistry. So I did my PhD in lithium-ion batteries. I worked with a prolific inventor, Jeff Dahn, and after that I wanted to continue working with an inventor. As you may know, in academia, there are so many different styles of research.

I mean, some people like microscopy and mechanisms, but I really like the creative aspect, like discovering something that could be useful or to solve problems. And not many academics and professors think through that lens. So I've always been very lucky to work with prolific inventors, both in my master's and my PhD. So for my postdoc, I sought to work with people who thought like that. So my co-founder, Yet-Ming Chiang at MIT, is a prolific inventor and also a serial entrepreneur. So Sublime is his 7th startup, and five of the previous six have been very successful.

So I didn't join him with the aspiration of becoming a founder. I really knew nothing about entrepreneurship or anything like that, but I did want to invent, and I did love the way he approaches his work from a problem-solving standpoint. So that's what brought us together.

David Roberts

And he's the one who sort of flagged the problem of concrete to you.

Leah Ellis

That's right. So I was always aware that cement was one of the biggest levers for decarbonization. But I suppose after my PhD, where I'd worked with one of the most illustrious battery scientists, I sort of always had thought that my career would be in batteries. Like, I thought I'd painted myself into a corner. And so when I first met Yet-Ming Chiang, he asked a question that at first I thought was a trick question. He was, "Hey, Leah, like, you've got this Canadian grant to come work with me, and I know you're a battery scientist, but aren't you a little bit bored of batteries?"

And I thought that was a trick question because he's the battery guru and I didn't want to insult him, but honestly, I sort of shared his opinion that, well, maybe this isn't his opinion, maybe it's just my opinion. But I think batteries are exciting, but I think there's like sigmoidal growth in any technology where it starts out slow to build momentum, and then it goes through a period where it's super hyped, and then you sort of squeeze all of the innovations out of things. And I think with lithium-ion batteries, which was my expertise, it comes to making the cans a bit bigger and the separators a little bit thinner and tweaks. And you know — I don't know, I just want to do something totally outside the box.

And I think that's what Yet offered me the chance to do when he said, "If you're bored with batteries, why don't we think of a way to apply our electrochemical toolbox to cement?" And so the way he came up with that electrochemical cement tagline was he spends a lot of time thinking about reducing the emissions in the utility sector. And I think we have all of the technology needed to do that. I mean, not saying it will be easy to deploy solar, wind, long duration storage, but at least we have the technology. So that's not necessarily where most of the early stage R&D is needed.

And so he was thinking at the time, like, how do we use low cost renewables, assuming that we'll figure out all of the utility stuff and really get to low cost intermittent renewables? And how do we take intermittent renewables and apply that to decarbonizing the next biggest tranche of emissions, which is cement? So cement, if it were a country, would be the third largest emitter after China and the US. So it's 8% of global CO2 emissions back in 2018, it fluctuates, but it's like 7% or 8%. So it's big game hunting when it comes to decarbonization. So we've always worked backwards from that electrochemical cement tagline.

David Roberts

And it's 8% of current emissions. But also, you make the point that's just going to go up, right? There's just going to be more and more cement as far as the eye can see.

Leah Ellis

Right. And as everything else, I hope, goes to zero. I think these so-called hard to abate sectors like cement and steel, they may be both seven or 8% now, but in