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.


(PDF
transcript)


(Active
transcript)


Text transcript:


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 coming years, as the grid
gets decarbonized, these numbers are just going to get larger
because neither cement nor steel are going to go away. And in
fact, we're going to use more cement, especially in places like
India and Africa, that will undergo a phase of dirty growth
unless we develop and deploy these clean technologies in time.


David Roberts


Right. So, let's talk about cement then. I mean, if you're
looking for the big problem with no solution yet, it seems like
you really nailed this one. So, let's talk about cement. I've
been reading sort of the background materials of your company and
reading about cement in preparation for this. I have tripled my
knowledge about cement over the last 72 hours, starting from an
extremely low baseline. What is interesting to me is that the
process whereby cement is made, the emissions mostly come from
trying to get lime. So, let's talk a little bit about how cement
is made.


So, cement, the recipe for cement, as you say on the website and
in all these briefing materials, is calcium silicate hydrate
(CSH). There are, I'm sure, details that matter, but that's the
basic recipe for the basic kind of cement that we've been using
for hundreds of years. CSH, they call it calcium silicate
hydrate, and that is made of lime and silica and water. We can
talk about silica and water later, but they're pretty easy to
come by. So, mostly it's about getting lime, it's about how do
you get lime? And the way we get lime now is starting with
limestone.


So, maybe you can just briefly describe the process whereby
conventional cement is made. How do we get from those raw
materials to the cement that we are familiar with in bags, mixing
with water, et cetera?


Leah Ellis


Yeah, as you say, cement, the principal ingredient is lime,
calcium oxide. And fun fact is, that's where Sublime Systems got
their name. I was looking in a rhyming dictionary for something
that rhymed. No shortage of cement puns. I can keep them coming
if you like. Or maybe you don't like.


David Roberts


That's excellent.


Leah Ellis


So, lime is calcium oxide or hydroxide. It's a reactive calcium
that reacts with silica and water to make cement. Or when cement
reacts with water, then it becomes concrete, that calcium
silicate hydrate phase you mentioned. So, today, and
historically, the path to making cement has been by thermally
decomposing limestone, which is calcium carbonate, which is 50%
by weight CO2.


David Roberts


Yeah, that kind of blew my mind. I don't know anything about
chemistry, so all chemistry blows my mind.


Leah Ellis


Yeah, it is mind-blowing. I mean, you think of cement, which is
the world's largest industry by mass. So we use more cement than
any other material besides water. And the prime ingredient in
cement, it's about 65% weight calcium oxide. And then that comes
from limestone, which is 50% by weight, CO2. So you just do the
math. It's very easy to visualize. Just the massive CO2 emissions
is staggering.


David Roberts


So the emissions from cement are almost all around this process
of getting lime. They're 50/50 — you break it down 50/50. So 50%
is getting the kiln hot enough to break limestone down, which
requires extremely high temperatures. What is it, 1400?


Leah Ellis


Yeah. So the way we make Portland cement, which is the modern
cement that we've been using for the past almost 200 years, is
you take limestone and then heat it first to 900 degrees Celsius.
And that is the temperature at which limestone decomposes into
reactive lime and CO2, and then to make Portland cement, which is
a specific chemistry of cement, you heat it further to 1400
degrees Celsius, at which point the lime and the silica fuse
together to make a phase called alite tricalcium silicate. And
then that is quenched. So it's dropped very quickly from that hot
kiln and sort of freezes that phase.


That when you grind the cement into a powder that now reacts very
vigorously with water, it releases a lot of that extra heat and
that turns into the hardened concrete.


David Roberts


So just to give people a visual here, a conception, this process
of heating lime up and getting the lime out of the limestone,
that's where all the emissions come from. They're about 50/50 the
emissions.


Leah Ellis


Yeah, about 50/50. And of course, it depends on the design of the
kiln. Some of them are more efficient than others, but it's about
50% limestone emissions, 50% fossil emissions. And to get to that
very high temperature, you often require a very high caloric,
luminous flame, which requires bituminous coals — is often the
primary fuel for this type of kiln.


David Roberts


Right. So it's 50% this special kind of coal heating up this
special kind of kiln to the extraordinarily high temperature of
1400 C. And then the other 50% is the CO2 in the limestone being
broken out and then vented, I guess emitted. Which is just the
reason I'm harping on this point, is just that I think a lot of
people think of decarbonization as primarily an energy thing. But
it's worth noting here that even if you find a decarbonized way
to get that heat, that 1400 C heat, you're still left with 50% of
the emissions. Right, because you still have CO2 coming out of
the limestone as it's heated.


Because we've talked a lot on this pod about alternative sources
of heat and about heat batteries, thermal storage batteries that
conceivably could get up to 1400. They have that in their sights.
But I just want to emphasize that even if that problem is solved,
you still got 50% of the problem left, which is all the CO2
that's embedded in limestone attached to the lime. So that's our
current cement. 50/50, heating up lime, breaking the lime out of
the limestone. Let's talk about ways that people have tried to
approach, before we get to Sublime's approach, let's talk about
other ways people have thought about this.


It's a big problem. And if you think about decarbonization long
enough, you end up here. What else have people tried to do with
cement? I know there are a couple of things floating around, but
maybe you just tell us sort of like, what are the other
alternatives here?


Leah Ellis


Yeah, there are, as you say, not many technologies, if any,
besides Sublime's, that can address both halves of the cement CO2
problem, the limestone and the fossil fuel, simultaneously. So
you could electrify the heat in some way with a thermal battery
or find some sort of electric kiln. And electric kilns have
material problems. It's difficult to get things that withstand
that temperature — the heating elements — if you're using
resistive heating, for example.


David Roberts


Is anyone doing that yet? Is there an electrified heat source
specifically making cement yet, or is that just an idea?


Leah Ellis


Not that I know of. I mean, I think that would be the obvious
solution, I think is to electrify the kiln. And I know there's
some efforts with plasmas and solar concentrators and stuff like
that, but I think that one would be, if it was easy, someone
would already be doing it.


David Roberts


Getting extremely high heat with electricity is vexing.


Leah Ellis


Right. And you can do it. The challenge is, like, can you do it
efficiently? And then even if you do it, have you really solved
the whole problem?


David Roberts


Right.


Leah Ellis


So, there's that. And then I'd say, like, what the industry is
doing right now. And to their credit, they are doing everything
they can to decarbonize, especially in the past three to five
years. So there's a focus on alternative fuel. So, cement
actually plays an interesting role in the garbage ecosystem
because it's such a high temperature. It's just a really great
place to dispose of things because everything at that temperature
vaporizes into CO2 within a matter of seconds. So it's a great
place to burn tires. It's a very clean way to burn tires.


David Roberts


What, in cement kilns?


Leah Ellis


Oh, yeah.


David Roberts


They're throwing tires in there?


Leah Ellis


Yeah, I've actually visited a kiln that had this tire injection
port, and I was able to stand on top of it and watch them drop
tires into this kiln. About every 20 seconds, a hatch in the
kiln, rotary kiln, would open, and it would drop in. I actually
have a video I can send you a link to. It's one of the coolest
things I've ever seen, but, yeah. The plant manager told me that
the tire turns entirely to CO2 within 20 seconds. I think many of
us have seen a tire fire which creates, like, black, choking
smoke.


But if you get to 1400 degrees C, it just undergoes complete
combustion almost instantaneously. So tires, like tar shingles,
unrecyclable plastic, medical waste, solvent waste. The list goes
on. In fact, I have an employee that used to work at a cement
kiln close to the US-Mexican border, and they would bring all
kinds of contraband that was seized at the border and they would
just unload pallets of contraband into the kiln. So, almost
anything goes. But that can't be your entire fuel source. So
that's a supplementary fuel source.


David Roberts


Does anything except coal work here? Like, is there a substitute
for this specialized coal here that can get to that kind of heat?


Leah Ellis


Yeah, I mean, some of them use like a blend of natural gas and
other things. And often it takes a blend of fuels to really get
up to that temperature. So first you have to start with propane
and get it to a certain temperature, and then you add more
oxygen. More coal is the typical fuel that's used. And so besides
all of these giant cement plants, if you look at them on Google
maps or something, there's usually you can see a little mountain
of coal besides the kiln.


David Roberts


Right, but for decarbonizing that, you basically just have to
capture the CO2 after it's emitted, right? From the kiln.


Leah Ellis


Yeah. So the ways the industry is decarbonizing now include
alternative fuels and then what's called supplementary
cementitious materials. And then of course, post-combustion
carbon capture, which hasn't yet been proven at scale. But there
are plenty of pilot plants because that's really the only other
way, in my opinion, besides Sublime Systems that can get you to a
fully decarbonized cement.


David Roberts


I mean, theoretically, right, that there's no carbon capture
working even close to 100%, as far as I know, on any industrial
facility. Theoretically, we could get to mostly decarbonized.


Leah Ellis


Theoretically. And I'm afraid to share your opinion that
post-combustion carbon capture has never been successfully
demonstrated at scale for cement and for coal either. I mean, I
sure hope it works because I think that is, if it worked, it
would be the most expedient way to decarbonize existing assets.
But I think there have been many challenges in employing
post-combustion carbon capture at scale.


David Roberts


Among other things, it basically doubles the operating cost,
right? I mean, it's just like adding another industrial facility
onto your industrial facility. And I just come back just on first
principles. I was like, however we solve this problem, it's not
going to be through some Rube Goldberg system where we double the
cost of every single concrete plant and then bury kajillion tons
of — and then build CO2 pipelines to all of them and then carry
all that CO2 and bury it. It's just like, there's no way that's
going to be it.


Leah Ellis


Yeah.


David Roberts


Although that's kind of where people are going. That's sort of
the only option.


Leah Ellis


I like to use the leaky tap analogy when talking about climate
change. So imagine you have a tap that's leaking or gushing
water. There's really three ways to fix it. And one is to stop
this flow of emissions and through carbon avoidance technologies
like Sublime Systems like renewable energy. And then the other
thing you could do is put a bucket right underneath the tap and
collect it point source. And of course, that's just a patch
solution if you don't have the means or the ability to fix the
tap right away. And that, of course, is point source carbon
capture.


And then the third way you could go about fixing this problem is
mopping the water off the floor. And in this case, the analogy is
director carbon capture, which is collecting the water in a much
less efficient, more energy-intensive, more dilute way. And I
don't think it makes sense to mop the water off the floor unless
you've done steps one and two to mitigate the stem of the flow of
CO2.


David Roberts


I just want to mention these materials you're talking about
adding to the process.


Leah Ellis


Yes, that's important.


David Roberts


Just to explain that. So you want the lime to react with the
silicates. That's the point of all this. But through this
process, you end up with a lot of lime sort of left over that has
not reacted with a silicate. And so you add these supplemental
materials and that kind of boosts more of the lime to react. Is
that basically right?


Leah Ellis


Yeah, that's right. So that phase that I mentioned that is made
in the kiln is called tricalcium silicate, or alite. And that is
three calciums, tricalcium to one silica. And then that hardened
phase of concrete that cement turns into as it hardens into
concrete is calcium silicate hydrate. One calcium to one silica
to one water, approximately. So Portland cement has three times
more calcium than it really needs. Those two extra molecules of
calcium are just on for the ride. They don't significantly
contribute to the strength or to the durability — in fact, they
make today's cement maybe less durable than, let's say, Roman
concrete was.


So this actually started decades ago. Let's say in the '60s, '70s
and '80s, people started using coal fly ash, which is a silicate,
and blending that into cement. And at first they did it to save
cost, because at that time, coal, fly ash, people would pay you
to take it off their hands and it dilutes the cement, so — they
did it for cost saving reasons. But really it makes better cement
when you balance out that calcium to silica ratio and you also
can lower your CO2 emissions. But that being said, you can only
lower the CO2 emissions of your concrete by about 30% before you
start having too much silica to calcium, and then that starts
deteriorating your performance.


So, there's fly ash, and that is going away. So the cement
industry is now moving, trying to find other sources of
supplementary cementitious materials. These include natural
sources of silicates like the Romans used, volcanic ash, so
pumice, certain types of calcined clays. All of these are being
developed as ways to dilute the Portland cement with no or low
emitting minerals, which do in fact make better concrete at the
end of the day. But again, these supplementary cementitious
materials can't, like, they can only solve 30%. Maybe you could
get to 50% if you accept some differences in performance, but
they can't get you to zero because these are bringing silicates,
they're not bringing that lime, and there's no way to decarbonize
lime, unless I think you're going about our process, which uses
renewable energy and non-carbonate sources of calcium.


David Roberts


Right. These materials you add, they're going to come back into
our story later. A little Chekhov's gun there. All right, so I've
made you and the audience wait for 20 minutes now. So let's talk
about how you solve this dilemma. So we've got limestone that has
to be broken down into lime. And right now, the only way we know
how to do that is heating it up extremely high with a fossil fuel
kiln, which emits things, and then you break it out of limestone
and it gets emitted. So you need basically what you and your
partner came to, where all of this sort of leads you as you sort
of analyze this process, is we need some other way to get lime.


Basically, that's the nub of the concrete problem. Basically, we
need a way to get lime that does not involve emitting a bunch of
CO2 as we break it out of limestone and does not involve super,
super, super high temperatures. We need a room temperature way to
create decarbonized lime. So I think anybody who sort of reviews
the process of how cement is made from a carbon perspective, is
going to end up there, right? Lime is the thing. So then you say
in your Medium post, once the goal was clear, it took us less
than a year of focused effort to invent a way to make carbon
neutral lime at ambient temperature, which kind of like, blew my
mind a little bit.


I guess it's just that no one had looked before. Or it's just
crazy to me that once you started looking, there it is. Which to
me indicates that they must not have been looking very hard
before.


Leah Ellis


I think that's true. I don't think people had been looking very
hard before, maybe for two reasons: So, one reason is that never
before have we had a pathway to low cost renewable energy. Which
is why something like this may have been invented decades ago,
but it wouldn't have made sense. So I like to call Sublime the
electric vehicle of cement making, because we're replacing these
high temperature fossil fueled kilns with something at ambient
temperature that avoids combustion but —


David Roberts


I love this. Can I just pause and clap here? Because I swear,
like, almost every one of my pods, no matter what technology
you're talking about in terms of modern technology you're talking
about, it's super, super, super cheap renewables that are
unlocking these possibilities, like one after the other. Stuff
that it would have been too energy-intensive and expensive to do
up until very recently. But renewables getting so, so, so cheap
is just like one after the other, unlocking all sorts of
possibilities in all sorts of areas. You wouldn't even
necessarily think, right, like cement. The first thing you would
think is like, renewable energy can do that, right?


But it turns out there it is again. There's cheap renewables
coming to our rescue yet again. Sorry, go ahead.


Leah Ellis


Yeah, well, totally. I mean, it expands your toolbox and just
like an electric vehicle, if you were to power your Tesla with a
coal fired power plant, I mean, there's really no point. Same
with us. We use the same or similar number of kilowatt hours in
terms of energy for our process. But if you're going to power
that with a coal fired grid or just fuel it with coal directly,
there's really no point. And so I don't think I'm really that
smart. I think someone 30 or 40 years ago would have arrived at
this conclusion. I think it's obvious in retrospect.


David Roberts


So many discoveries seem that way, right?


Leah Ellis


Yeah. And then the other reason why I think my co-founder and I
were special in being the ones to discover this obvious in
retrospect pathway is that we blurred the lines. I think many
people, especially in academia, they're sort of pigeonholed into
their area of expertise. And I don't even credit myself for this
move. I think it was my co-founder, who's a tenured professor at
MIT, very celebrated. He's already made his career, so he's quite
comfortable putting it on the line, being exploratory and
cross-pollinating two disciplines that don't see each other. Like
civil engineering, is where cement lives.


Electrochemistry is in material science or in the chemistry or
physics departments, and those often don't touch. And the grad
students may not even meet each other on campus. And so I do
think it required a certain degree of boldness and courage on the
part of my co-founder. And I was just trying to make him happy
and be his conspirator and co-inventor, but that original concept
definitely came from him.


David Roberts


So let's talk about how you do it, then, how you make lime with
an ambient room temperature process that does not produce CO2. It
turns out to involve another theme that comes up a lot on Volts,
turns out to involve an electrolyzer. So, walk us through a
little bit how you end up with lime.


Leah Ellis


Yeah, and I have to say, it may be quite simple in retrospect,
although there's a lot of high tech technology and patent
applications will be filed. But at a high level, it is so simple.
I can explain this to someone with high school chemistry. So,
when you do water splitting, you make hydrogen at one electrode,
oxygen at the other electrode. But if you start with neutral pH,
water or a brine, you make acidic solution at one electrode and
an alkaline solution at the other electrode as a function of that
water splitting reaction. Now, once you have that pH gradient,
you can use it to drive a chemical reaction.


In this case, the dissolution of calcium from a mineral. If
you're using limestone as a source of calcium, which we don't,
you can think of this as like a Mentos and Coke reaction, where
you have a carbonate reacting with acid to dissolve those
minerals and release the CO2. So we could use limestone, and we
could capture all that CO2, which, just like the Mentos and Coke,
the CO2 would be cold, clean, and compressed. If we do this in a
pressurized unit, and we could likely collect a lot of money for
45Q tax credits. But we chose to abandon that path and go for
that true zero approach of using a non-carbonate source of
calcium.


So, there are many calcium silicates, both natural minerals and
also waste materials that are calcium silicates. We can dissolve
the calcium from those minerals, leaving behind a reactive
silicate. Those calcium silicates are inert. You put it through a
reactor, the acidic side of the electrode dissolves the calcium,
leaving behind a — so we've broken those inert bonds — leaving
behind a reactive silicate. Then the calcium swings over to the
negative electrode, precipitates as a hydroxide. Now you have
reactive calcium, aka lime, and you have a reactive silicate and
you dry those off into free flowing powders, blend them together,
and now you have a cement that is very much like Roman cement
where Romans, they didn't make Portland cement at 1400 degrees
Celsius.


They made what's now called a pozzolanic cement, where they took
volcanic ash, the silicate, and they took lime, which they made
at 900 degrees Celsius, that first step. And they blended those
together with water to make a cement that has evidently stood the
test of time. So we're following that old recipe.


David Roberts


It's all lime, silica and water.


Leah Ellis


At the end of the day, yeah.


David Roberts


At the end of the day you're getting your lime. So you're
precipitating lime out of lime containing calcium silicates.


Leah Ellis


That's right.


David Roberts


And so that would be your raw material instead of limestone. So
just on the materials side, you're going to need a lot of
whatever that is. What is that going to be? What is that material
that you're going to break the calcium out of that you're going
to be able to find in bulk that does not contain CO2?


Leah Ellis


Yeah, broadly, it's basaltic minerals. So anything with 10%
calcium, more or less could be a suitable input material. So
basaltic minerals, this is the type of rocks that are typically
used as aggregate in concrete. So we can almost use the same
supply chain that people use for aggregate can be used as input
for our material as well.


David Roberts


So there's no choke point there. That's an abundant material.
There's no worries about finding enough stuff, basically.


Leah Ellis


Yeah, that's right. There are no worries about finding stuff.
Although of course, even for cement plants today, making sure
that your quarries are in close proximity to your market, it is a
big exercise to site a plant and to minimize transportation costs
because cement is so massively produced, which makes it very
cheap and it's also very heavy. So there is a game here that we
are also playing alongside any other cement company about siting
your plants in proximity to market or in a way that you could
float it by boat, since that way it travels very inexpensively.
So you find cement plants on the Mississippi River, on the
Hudson, near ports where the cement can float.


David Roberts


Got it. You know, you're talking about using just sort of
aggregate, just sort of like junk rock as an input. Is there any
input you could use where getting rid of it would actually be an
extra value stream? Like some sort of waste that you could
dispose of by doing this.


Leah Ellis


We have looked at loads of waste. So we have an ARPA-E grant that
looks at ponded bottom ash. So there's billions of tons of ponded
bottom ash. Like historical. So this isn't the fly ash, the stuff
that comes out of the top of the smokestack. This is like the
bottom ash, like the stuff with heavy metals that sort of is at
the bottom. It's the icky stuff that they've ponded for hundreds
of years. So there's billions of tons of this that needs
remediation. This is the stuff they'll pay you to take it away.
And with our process of dissolving the metals, extracting it,
leaving behind a silicate, and then precipitating the metals and
isolating them, could be a way to clean up bottom ash.


We've also looked at other things, like you could even use our
system to recycle demolition debris. So dissolving the cement and
turning it into fresh cement. We've looked at eggshells, we've
looked at municipal incinerated waste, we've looked at
clamshells, I don't know. For s***s and giggles we've tried out a
laundry list of things to make sure they work. But really what
we're going for is to optimize our process around materials that
are widely abundant, and especially in places like India and
Africa. Because Sublime's stated mission is to have a swift and
massive impact on global CO2 emissions.


And we know that both India and Africa are going to undergo a
period of dirty growth if their population is going to grow and
enjoy the same quality of life that we do, and if they build
carbon intensive cement and steel plants. Those plants are
designed to last 50 to 100 years. So if we work quickly to scale
up this technology, we want to make sure that all greenfield
cement plants in these developing regions are made with
technologies that will avoid CO2 emissions for decades to come.
So we really have a small window of opportunity to really get
ahead of generations worth of CO2.


David Roberts


Yeah. So you need a cheap and abundant feedstock, which makes
sense. But getting back to this, like, say you're using bottom
ash, the way you're getting lime out of this stuff is that lime
precipitates out at a particular pH level, right? Sort of like a
threshold. And presumably other chemicals will precipitate out of
that mess that you throw in there at other pH levels.


Leah Ellis


Different pH. Yeah.


David Roberts


Right. So could you, if you're just dumping a bunch of sort of
bottom ash slurry into your machine, you can pull out the lime.
Can you also pull out some of the other, like those heavy metals
you're discussing that we don't want in our water or soil? Could
you precipitate those out too? Like, can you isolate other things
other than lime if you wanted to repurpose this in the future for
some reason?


Leah Ellis


Yeah, you could. And in fact, if we're using basaltic minerals,
those aren't only containing calcium and silica. Those are also
containing iron, magnesium, aluminum, which we are isolating as a
function of our process, like you say. And what my director of
R&D likes to say is, "We use the whole rock just like hunters
use the whole deer." So all of these things are coproducts. And
in fact, things like magnesium are actually worth more than
cement.


David Roberts


Oh, really?


Leah Ellis


We're actually not — yeah, I mean, it's a fine chemical.


David Roberts


Are you pulling out enough magnesium out of these materials that
that could be a —


Leah Ellis


So it could offset the cost?


David Roberts


Yeah, like a meaningful value stream.


Leah Ellis


I mean, we think so. Although our focus is cement, we know that
people invest in us to have that swift and massive thing. So we
are focused on doing this cement work. And everything else is
just gravy. We actually haven't factored those costs in and done
that business development work to see how much it sweetens our
cost, because we're just focused on making the cement. And I have
to say one of the reasons why Sublime has a cost advantage over
other ways of decarbonizing cement is that, as you said before,
we're not adding on to a Portland cement kiln.


Adding carbon capture is going to at least double the cost of
making cement. And because our technology is carbon avoidance,
it's green cement, not blue cement. We are replacing the kiln
with a new technology. Now, we may not be able to compete on cost
with our first plant because cement has undergone almost 200
years of improvements and redesigns of the kiln where they had
wet kilns, semi-wet kilns, and dry kilns. And finally, these
five-stage preheater, precalcinator kilns, which I won't get
into, but they've undergone tremendous efficiency improvements
over the past 200 years. And so we think we can get really,
really close.


And I don't think any other technology can do that because
they're always adding on to a Portland cement kiln.


David Roberts


I mean, it seems like if you could sell the magnesium, you bring
down the cost of your cement and make it more competitive.


Leah Ellis


Totally.


David Roberts


So instead of a kiln, you have an electrolyzer, which does not
require high heat. All this process you're talking about with the
metals precipitating out is an ambient room temperature process.
Yes?


Leah Ellis


Yup.


David Roberts


And you end up with lime. And then you can mix lime with the
silicates that you also got out of your raw material. Or do you
have to bring in extra silicates to mix with the lime? Once
you've got the lime. And what are they?


Leah Ellis


No, we're using our own silicates. And of course, if we want to
get the desired calcium to silica ratio, it may mean blending in
certain inputs to get to the right ratio. But yeah, it's just a
tweak to get the input ratios to match the output ratios of what
we want.


David Roberts


And so this cement that you are producing with electricity and
non-CO2 containing rocks, I assume you have produced it. And it
has been through whatever tests, whatever governing bodies put
cement through?


Leah Ellis


It has. So our cement meets what's called ASTM C1157, the
performance-based specification for hydraulic cement. This was a
standard that was created 30 years ago. And really this standard
is so important because previously cement was defined by the
crystal structure of what was made in the kiln. So that alight
tricalcium silicate phase that you can only make, it's only
thermodynamically stable at those volcanic temperatures. So you
cannot solve for alite, you know, unless you go through that
thermal process. So, actually, when we were at MIT, my co-founder
and I, we believed that if you weren't making Portland cement,
nobody would use it.


That was the prevailing myth at the time. I got out and networked
with the industry and spoke to the customers and realized that
people who work at a readymix concrete producer, those folks
running the spinning trucks, they don't know what alite is.
They've never heard of tricalcium silicate. They talk about
slump, they talk about alkali silica reactivity and set time and
finishing properties. And so we realized that it was the
performance of this cement that matters. It's not the chemistry
and the standard bodies have prepared for this moment. And all of
this work with supplementary cementitious materials, which are
gaining traction, especially in Europe, is just winds of change
that are blowing in the right direction.


Because as you start blending cement with other things, it
becomes much less about the chemistry that you're making in the
kiln and more about the ultimate performance.


David Roberts


So the standard is about performance.


Leah Ellis


There are multiple standards. So there are three standards baked
into the international building code. One is for pure Portland
cement. The second one is 50% Portland cement, 50% SEM. So a
blended cement. And then the third one is pure performance-based.
So we don't care what you do, as long as whatever you have
performs this way. And there's an exhaustive list of tests that
you have to do. You want durability and strength and freeze-thaw
and chloride ingress and all these different things that you test
to make sure that your cement is performant. So we've done those
tests.


We do them in-house. We have a world-class cement testing lab,
but that's not good enough. We send it out to an accredited
third-party lab, we test it again, and then — just so that we
don't waste our customers' time — and then the third test is done
by our customers. And that's really the test that matters. And so
this quarter, we finished our pilot plant early January this
year, and then spent a few months optimizing our production,
ramping it up, testing it in-house, testing it with the third
party, and now we're testing it with the customer, and the
results have come back very strong, positive, and we're working
with some of the best people at Boston Sand and Gravel.


David Roberts


Well, presumably, what you would want to hear from a customer is
just nothing. They just used the cement and it worked fine and —


Leah Ellis


It works exactly.


David Roberts


There's nothing to report. I said those supplementary —


Leah Ellis


Cementitious materials.


David Roberts


Yes, thank you. I said they would come back into the story. Those
supplementary materials that are being added into traditional
cement to incrementally lower its carbon intensity, those are the
silicates that you're using to mix with your lime. So you're
actually just using the lime and the supplementary materials and
just skipping, basically, the Portland cement kiln part of it.


Leah Ellis


Yeah.


David Roberts


And so you've produced this cement that is now passing
performance tests being used in the field. It's working well. One
point I did want to make before we leave behind the process part
is if you use a feedstock that doesn't have CO2 in it and you use
renewable energy to power your electrolyzer, then you've got bona
fide zero carbon cement, the holy grail. But you make the point.
And I think this is maybe just worth pointing out. Even if your
process uses limestone as its feedstock and thus has CO2 in it,
and even if it uses average US grid electricity.


Right, which is not clean. Even if you do both those things, you
still end up with cement that's lower CO2 than conventional
cement.


Leah Ellis


That's right.


David Roberts


So basically, switching to this process immediately improves the
carbon performance of cement, even if you don't have your
electricity and your feedstock dialed in perfectly yet.


Leah Ellis


That's true, although we will accept nothing less than
perfection.


David Roberts


Well, you say in the medium post that you're currently 70%
decarbonized. Does that just mean there's still some limestone in
the process?


Leah Ellis


Yeah, exactly. But it is our goal to get to 90%. And so when we
model our megaton plant with optimized feedstocks, optimized
electricity, we just did a lifecycle assessment with Climate
Earth, which is the cement industry's preferred lifecycle
assessment partner. So we did show that we can get to 90% lower
emissions than today's Portland cement using our process at
scale.


David Roberts


Why 90 though? What's the 10% left over?


Leah Ellis


Oh, I believe that was from the mining and transportation. And
those are sort of outside of our gates. So again, if you're
traveling by truck or going back and forth between the quarry and
the kiln and that type of thing.


David Roberts


Ah, interesting, interesting.


Leah Ellis


But I'm sure those will go to zero too, as all those heavy trucks
get electrified.


David Roberts


So, your big plant that you are envisioning here, your mega-scale
plant, your full-sized plant to be certified as basically super
low carbon, let's say 10%, 90% carbon-free, you're going to have
to find the right quantity of feedstock, a non CO2 containing
feedstock, a steady, large supply of that, and you're going to
have to somehow certify that your electricity is completely
clean, which is going to get you in the same sort of tricky
situation that the hydrogen people are in right now, which is how
do you certify that electricity is totally clean? You can't just
use grid electricity, right? Because then you're taking the clean
electricity from someone else. You basically are going to have to
like — it's additionality.


You end up with the additionality problem. I don't know, that's
probably way down the road for you. Maybe you haven't even
thought about that.


Leah Ellis


Well, we do think about this. So we have a kick-ass head of
project development and strategic sourcing. So shout out to Becky
and she's doing the work to cite our megaton plant. And we're
looking at places that have renewables. And I know the hydrogen
folks, as you say, struggle with this too. So we require —
anything six cents a kilowatt hour or less is fine with us. And
we're looking to site first in places with a high degree of
renewables. And again, it doesn't have to be zero, although zero
would be great, but it's just as low as reasonably possible.


David Roberts


Would you ever build your own renewables attached?


Leah Ellis


Yeah, we might. We're looking at that too. And then to your
question of additionality, we're actually gearing up to publish
something recently that shows that because Sublime Systems is a
great way to use a renewable electron because it has similar
embodied energy as today's kiln. But you're not just using that
renewable electron to replace a fossil electron, you're also
getting avoided carbon through avoiding the limestone as well.
And so when you calculate the amount of CO2 avoided per kilowatt
hour, you compare that over many other technologies using that
the highest and best use of a renewable kilowatt hour could be
for Sublime cement.


David Roberts


Interesting.


Leah Ellis


According to our calculations.


David Roberts


Interesting. So let's talk a little bit about scale and about
cost. Right now you've got basically a little lab set up. You're
producing this stuff, but on a very small scale.


Leah Ellis


Well, I wouldn't call it little. It is a fully functioning,
continuous pilot plant that can do up to 250 tons a year. But it
is small. And we affectionately call it our cement plant for
ants, if you know the Zoolander reference.


David Roberts


Which is just to say that scale will bring lower costs.


Leah Ellis


But totally, it's all about scale.


David Roberts


Right. Insofar as you know, the costs now, currently, because as
you say, traditional cement is very cheap. So are you currently
in the ballpark or what's the sort of timeline? How do you see
getting into the ballpark? Where are you now and where are you
kind of targeting?


Leah Ellis


Right. So where we are now is definitely less than cement plus
post-combustion carbon capture.


David Roberts


That's a low bar, but yes.


Leah Ellis


Well, is it a low bar? So one of the things is that cement is
very inexpensive, and that is a double-edged sword for us. So
that makes it very difficult for us to compete on cost with a new
technology that hasn't yet achieved scale. But on the other hand,
that makes it — the so-called green premium — really that small.
Especially when you compare it to other things like direct air
carbon capture or sustainable aviation fuels. And also, if you
think about the total installed cost of concrete. So 80% of the
total installed cost of concrete is labor, and it's often
unionized labor.


The cement is 10% of that, and the aggregate is the remaining 10%
so even if we were to charge a two to four x green premium,
really, it doesn't really affect the overall cost of a building
that much.


David Roberts


Right.


Leah Ellis


But your carbon savings are huge. So, again, if you're thinking
all across clean tech, that green premium or the carbon credits,
if you think of dollars per ton of CO2 captured or avoided, I
think Sublime cement is really attractive. When you do that
analysis, especially as we come to scale.


David Roberts


How big does the green premium need to be currently to bring you
down to Portland cement costs?


Leah Ellis


Yeah. So presently we're scaling up. I mean, I don't even dare
calculate what it costs at pilot scale because it's so handmade.
But at this next level of scale that we're doing. So between
where we are now, which is pilot scale, and where we need to be
at megaton scale, we do have to build what we're calling the
kiloton plant.


David Roberts


An in-between plant.


Leah Ellis


Exactly. An in-between plant. And that is to validate the
product, the process, the economics, the performance, to enable
us to attract low-cost project finance so that we can build the
megaton plant, ideally many megaton plants, and work with
partners to deploy this all over. So at that megaton plant, you
don't have the economies of scale that we would have at the
megaton.


David Roberts


Kiloton


Leah Ellis


Yeah, at the kiloton. You know, we like to say the megaton plant
is like achieving Costco level status. And at the megaton plant,
I do think we'll be able to compete on costs.


At the very least, we'll be able to undercut cement decarbonized
by post-combustion carbon capture by a long shot. So I'm very
confident saying we'll be the cheapest low carbon cement,
especially after we crunch the numbers with all the co-products
that you mentioned. But at the kiloton scale, I think this is at
the farmers market pricing. So the people who will be taking
offtake from our cement, from that plant, they will realize that
they're paying a higher price for something that's special, for
something that comes with the added value of a lower profile of
harm against the planet.


And the premium that they're paying is reinvested into our
technology, into the people that are making this happen, and that
it is very much catalyzing this technology that I believe will be
obvious in retrospect in a post-carbon world.


David Roberts


Right. Well, they'll have warm feelings, but I think there are
also — we'll talk about this in a second — but there are also
some entities who are under sometimes self-imposed, sometimes
legally imposed requirements to find low carbon cement. Some
people are doing it because they need it, not just because
they'll feel good about it. So, scale wise, the kiloton plant is
roughly when?


Leah Ellis


So that depends on a lot of things, but we're ready to have that.
We are on track to have that built and commissioned and
operational by early 2026. But of course, that timeline requires
everything to go perfectly. But we're all geared up for that.


David Roberts


And that will be a working, like, you'll be selling concrete.
It'll be a full-size selling concrete plant. No longer just a
test or a demonstration.


Leah Ellis


That's right. We'll be selling cement to concrete producers.


David Roberts


And then, assuming everything goes well. Of course, everything
never goes well. Assuming everything goes well, you have your
kiloton plant in early 2026, you're selling cement, it's working,
your customers are happy, your financiers get more confident.
They extend to you some low-cost capital for you to scale up.
Then you build your megaton plant, everything goes well. When
does that happen?


Leah Ellis


That could be as soon as 2028. Again, these are very aggressive
timelines, and this assumes everything goes well. But once that
kiloton plant is built and validated, assuming we have sites
ready to go, those megaton plants could be built as quickly as
within two years.


David Roberts


And then a megaton plant produces how much?


Leah Ellis


A million tons a year.


David Roberts


A million tons a year. And so to replace any meaningful amount of
cement supply, you would need a bunch —


Leah Ellis


Hundreds of them.


David Roberts


Hundreds of those eventually. Have you thought about, I mean,
you're selling cement. Have you thought about licensing the
process and just having other people work on joining you and
trying to scale up?


Leah Ellis


We do all the time. So, like I said before, we're capitalists
around here, as you know. So I hope we'll make a healthy profit
for the investments. But the goal is to have a swift and massive
impact on global CO2 emissions as quickly and as bigly as
possible. And I hope we'll make money along the way, and I expect
we will, because that's how value is measured. But really, it's
all about speed and scale, because we could do this ourselves.
But really, I'll just be honest here, we're nerds. What gets us
fired up is this technology and the product that we're making.


There's a lot that we don't know. One of the reasons why the
cement industry has taken so long to change is because innovation
is not part of their DNA, per se. They run operations like
nobody's business. They keep these megaton plants up and running
around the clock with high-quality, reliable material that's
distributed in the most efficient way to get everything built
with minimal disruptions. It's really, truly remarkable.


David Roberts


Yeah, you pretty quickly get beyond the science part to just
logistics and stuff like that. There's like a whole set of those
considerations for large-scale businesses that are unique to
scale, I think.


Leah Ellis


Exactly. So the operational know-how is there. And I think we
would be foolish to try and reinvent the wheel entirely by
ourselves. And I mean, would we be able to build? So let's just
say we address half a gigaton of CO2 emissions per year. So
cement is 8%. Let's say we set our expectations low, aim for 1%
of CO2 emissions or half a gigaton. That's like 500 megaton
plants. So how will we get to 500 megaton plants by 2050, if
that's our goal, working backwards, we would need at least ten up
and running by 2030, let's say.


So I really think if we're going to get this s**t done, we have
to take what we do well and merge it with what the industry
evidently does well, which is the operational logistics and
know-how. And so, we speak to cement majors almost every week,
and they're coming to us, and they have a legitimate desire to
not be the world's largest CO2 emitters. And this is also an
interesting fact. So cement companies, they have the highest
scope one emissions of any company. You would think it's Aramco
or Exxon, but no, they're making fuel that other people are
burning. It's cement companies.


David Roberts


Yeah. Scope three, that gets the oil companies.


Leah Ellis


Yeah, totally. But cement companies, it's their scope one, so
they have a great big X on their back, especially in Europe.


David Roberts


Well, it also seems like, I know there are improvements. It's not
fair to say that you're sort of stuck with what you're stuck with
when you're using fossil fuels. I know there have been
improvements in the kiln process and in the input and the kind of
kiln, but there's a certain sort of baseline, like when you're
using limestone and you're using Portland cement process, there's
a certain floor, right? Whereas when you're using electrolyzers
technology and you have a bunch of different feedstocks to choose
from and a bunch of different metals that you can pull out of
those feedstocks, it just seems like you're opening up a lot of
new areas for innovation.


Basically, the runway for cost declines seems huge here.


Leah Ellis


Yeah, I believe so too. And I think what's really exciting is
that if Sublime succeeds, and I believe we will, that technology
that we're starting to build now, and that will continue to
improve over time, will be the way we make cement for the
post-carbon world, like, for the next millennia. So I feel like
this is a really cool place to be where cement innovation
happened with the Romans. And we still go back and visit those
monuments that they made. And then cement was innovated a second
time by the British with Portland Cement. And now we're creating
new cement in America that's for this post-carbon world.


And so often when you think of buildings and the architecture,
the way you make a building is often a representation of the
values of the people who've built it. And so I think it's a very
exciting time for us to be making this new material and to be
incorporating it into the most cutting-edge buildings that we're
building today. For some of the best and most forward-thinking
companies.


David Roberts


These electrolyzers, are they a special kind of electrolyzer that
you need custom built, or are these just normal, off-the-shelf
electrolyzers? What is there to say about the electrolyzers?


Leah Ellis


They leverage a lot of existing technology. So electrolyzers
broadly are very similar. You've got electrodes, often with a
carbon backing, often with a rare earth catalyst, you've got
separators. There's kind of like assembling a sandwich of
electrode, separator, electrode. And so many components of our
electrolyzer exist and have been scaled up to megaton scale, and
we're simply taking that and leveraging that for our own
purposes.


David Roberts


So like your own kind of sandwich, but made with standard
ingredients.


Leah Ellis


Exactly. We're taking the bread and the mayo and the lettuce, and
we're just slapping them together in our own special way.


David Roberts


Right, but in terms of electrolyzers for your process, you're the
one making them. So that'll scale up too, and presumably get
cheaper too.


Leah Ellis


Yeah, exactly. And I think many of the trends we see with
hydrogen and all these other electrochemical things taking off, I
mean, we do anticipate that as well — we've got the dropping
price of renewable electricity, especially intermittent renewable
electricity — and I believe we'll also see electrolyzers come
down in price as well.


David Roberts


Yeah, yeah. I talked to the woman in Iceland who's making ammonia
directly with electrolyzers. I clearly need to wrap my head
around electrolyzers better and do a whole episode on
electrolyzers, because I had thought they were just for hydrogen,
but now people are doing all sorts of other things with them.
Anyway, so final, I promise, question: What sort of policies
would help you? I mean, I think some of them are obvious, just
like lowering, requiring lower CO2 emissions, maybe requiring
government procurement. Like government could say, we're going to
buy lower cost cement. What are the other sort of big buckets of
policy that you think would help accelerate this process?


Leah Ellis


Government procurement would go a long way because the US
government, in its various forms, army, GSA, federal highway
administration, DoT, procures 60% of the cement produced in the
US.


David Roberts


Oh, wow.


Leah Ellis


So if we don't have a commitment from them that they want this
cement, it makes it more than twice as hard. But the policy
change that I would really like to see, and what really grinds my
gears is that when you look at tax incentives and production tax
credits and also the voluntary carbon market, they reward
disproportionately direct air carbon capture. For example, I'm
forgetting the acronym. Is it 42? Oh my gosh. Can you remind me
what?


David Roberts


45Q? That's the carbon capture one.


Leah Ellis


C three. Anyway, the carbon capture one, it's $180 a ton for
direct air carbon capture, $80 a ton for point source carbon
capture, and zero for carbon avoidance. And we applied for a
production tax credit for our low carbon production of cement and
we were discouraged from submitting a full application. And I
think it's unfair, using that leaky tap mop bucket analogy, that
you should be incentivized more for mopping up CO2 than for
fixing the tap. And I believe there should be a technology
agnostic implementation of the tax credit to put all of these
things on a level playing field and then let the invisible hand
of capitalism choose the most efficient way to decarbonize.


I don't think the government should be picking winners.


David Roberts


Well, this is the danger of industrial policy, right, is that
once you get down in the gears, you're going to inevitably sort
of get some things and skip other things and get out of balance.
Presumably there are other policies besides carbon capture,
policies that would help you, right?


Leah Ellis


Yeah, I actually think direct carbon capture is great. I'm
definitely not anti-direct carbon capture. I'm just advocating
for carbon avoidance to be valued the same as a ton of carbon
removed from the air, especially when the carbon avoidance is
technology enabled, like Sublime Systems. I think there's a role
for this premium, this farmers market stage that we're at, to get
that added boost so that we can get to a stage where we don't
need that incentive anymore. But you will never get there with
DAC. It'll always need to be propped up somehow.


David Roberts


Yes, I know. Have you gotten help from the LPO? From the loans
office?


Leah Ellis


No, they haven't helped us yet. Although had some interesting
conversations with Jigar Shah and others from the LPO. And I do
hope that once our kiloton plant is built, we will definitely
work with LPO.


David Roberts


It seems so obvious this is such a huge opportunity here and
exactly at the stage of business that they're designed to help.
Okay, so some sort of production tax credit would be great. Some
sort of government procurement strategy. Is there anything like
that in place? Is there demand pull? I know that a bunch of
companies are saying they want to reduce their own emissions. A
bunch of concrete companies are saying, where are we at on demand
pull? Like, is there a big developing market for low carbon
concrete that's going to help pull you through this?


Leah Ellis


I am seeing huge demand for low carbon cement and I would say
that our customers are leaning into us just as much as we're
leaning into them and they want more of it sooner. It's one of
those things, though, that's difficult to manage. And I think
maybe like setting up a carbon market, people are not used to
seeing new products in the cement world and so getting these
advanced market commitments and these offtakes. Right now, when
people build a new cement plant, cement is vertically integrated
with concrete, oftentimes. So you never need an offtake for
building a new cement plant and even the supplementary
cementitious materials.


The industry just knows that if the product meets a certain
quality, that there will be, at a certain price, it will be
bought.


David Roberts


Right, right.


Leah Ellis


So these offtake agreements have sort of never been done before
until now. But, yeah. so we're still in the stage of figuring
that out and standardizing those agreements. And one day I hope
there will be a sort of book and claim model for selling our
material as well as other low carbon cements.


David Roberts


Yeah, it does seem like, especially once it's wider known that
this is available and that it performs as well, it just seems
like there's just going to be huge demand from every which way.
Leah, this has been absolutely fascinating. I've been meaning to
dive into concrete forever and this was a good excuse to learn.
It's funny. I'm going to finally learn how it works right on the
cusp of it changing to a new process. But thank you so much for —
I feel like you've really found the right target here. This is
such a leverage point for so much change.


So thank you for coming on and walking us through it.


Leah Ellis


Thank you so much for having me, and for being an enthusiastic
listener as I talk about my favorite subject for a full hour.


David Roberts


Awesome. That's what we're here for. All right, thanks so much.


Leah Ellis


Thank you.


David Roberts


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