Imagine a bustling city with towering skyscrapers, busy roads
and people going about their daily lives. It's a picture of
modern civilization. But there's a hidden cost. The very fabric
of these structures, the concrete, is a silent giant in
terms of greenhouse gas emissions, responsible for 8% of
global total. Concrete is the second most used substance in
the world after water. Its role as a building material is so
woven into the fabric of our lives that it's almost invisible
in plain sight. If you're sitting in a building right now,
you are in essence cradled by concrete. But what makes
concrete so indispensable and strong? The secret ingredient is
cement. Cement is what binds everything together and gives
concrete its strength and it's also where most of the emissions
come from. In 2021. More than two and a half billion tonnes of
CO2 are released from cement production. While cement and
concrete can be recycled, the demand far outstrips the amount
recycled each year, which means we have to produce a lot of
fresh cement. There are things we can do to limit how much we
use. But because developing countries are using increasing
amounts of cement to build housing and infrastructure to
improve living standards of their booming populations, we're
going to need more and more each year for a while yet, that means
we need to find a way of producing it without the
emissions. And unfortunately, cement making is likely to be
one of the most difficult sectors to decarbonize. But
though it's difficult, it's by no means impossible. In this
video, we're going to take a look at how traditional cement
production works, where the CO2 comes from in that process, why
it's so hard to get rid of and how we can make cement without
any CO2 emissions. I'm going to try and make the abstract
concepts a bit more... concrete.
I'm Rosie Barnes. A mechanical engineer with a PhD and a couple
of decades experience developing energy transition technologies.
Welcome to Engineering with Rosie.
Let's start by laying a foundation and clearing up the
difference between cement and concrete. These terms are
sometimes used interchangeably, but they're not the same thing.
Concrete is a mixture of cement along with sand and gravel which
is used as a building material and water is added to the
mixture it forms a fluid like slurry that allows it to be
poured in place where it will harden over several hours most
concrete is poured with reinforcing materials like rebar
to increase its strength. Cement is the most important ingredient
of concrete as well as other building materials like mortar
for masonry. It's the part of these materials that makes them
stick together and it's almost never used on its own. There are
different kinds of cements. By far the most commonly used today
is Portland cement. Its main ingredient making up to 95% of
it is a substance called 'clinker' and the other
ingredients are gypsum and fine limestone. The clinker acts as
the binder in cement and production of clinker is what's
responsible for most CO2 emissions from cement. So quick
recap clinker is the main ingredient of the most commonly
used type of cement, cement in turn is the main ingredient of
building materials like concrete.
I mentioned that emissions from cement are going to be hard to
get rid of in order to explain why I'm going to quickly take
you through how it's produced. First, limestone, calcium
carbonate rock, is crushed and ground to produce a powder
called Raw Meal which also contains supplementary materials
like silica, alumina and iron that are needed later in the
process. Next, the Raw Meal is heated in a kiln in one or
several stages. At around 900 degrees Celsius the calcium
carbonate in the limestone begins to decompose in a process
known as calcination. This composition releases carbon
dioxide and leaves behind calcium oxide, the CO2 is
emitted into the atmosphere and this part alone is responsible
for about two thirds of the emissions from cement
production. The CO2 that's emitted here is a non negotiable
part of that reaction because limestone is 44% CO2 by weight,
which is trapped in the rock and it's released when making lime.
If you want to turn limestone into lime, you simply cannot
avoid releasing CO2. As the temperature increases to around
1450 degrees. calcination continues and the calcium oxide
reacts with the silica, alumina and iron to form compounds known
as clinker minerals. The really hot temperatures needed for this
process usually come from burning fossil fuels, resulting
in more CO2 emissions. Burning fossil fuels isn't the only way
to heat things. But the high temperatures needed rule out
some of the easier clean heat alternatives like heat pumps,
and it's these problems together that makes eliminating cement
emissions so difficult.
But there's nothing that engineers like more than a
problem. And engineers and other experts around the world have
developed a number of methods to reduce or remove cement
emissions. So let's go through those now. To start, we can
reduce emissions from cement just by using less of it, we use
far more cement than we need right now. A lot of the building
standards for instance, require a certain amount of cement when
what they're really trying to accomplish is a minimum amount
of strength. This result in using a lot more cement than
necessary a lot of the time. Moving from material standards
to performance standards would be a good way to deal with this.
Another thing that would help reduce cement usage would be
increasing the recycling rate of concrete. Estimates for current
recycling rates vary a lot from as low as 20% to as high as 80%.
So there's at least a little bit more we can do and maybe a lot
more. The components of concrete can be partially recovered and
reused when an old building is demolished as long as a clean
source of energy is used for the heat needed in the recycling
process, emissions are negligible compared to virgin
cement production. There are also several technological
solutions for reducing cement usage, a company called Carbon
Cure has developed a technique that involves injecting CO2 into
concrete. They claim that this actually increases its strength
and because it's stronger around 4 to 6% less cement content is
needed. And as an added bonus, the injected CO2 stays there
permanently with about 13 kilograms of CO2 per cubic meter
of concrete sequestered. The use of geopolymers as a cement
substitute is another option. Geopolymers are a type of
cementitious material that can be made from a variety of
materials including fly ash, slag and recycled concrete.
Because they don't use limestone and they don't need high
temperature processes, their manufacture can be up to 70%
lower emissions than traditional cement. Aside from replacing
cement with low emissions alternatives, another
possibility is to lower the clinker content of cement.
Because clinker is the emissions intensive part of the process, a
lower clinker content means lower emissions, the global
average clinker content is about 65% and the average in China is
about 57%, with the difference coming from what's known as
supplementary cementitious materials mainly industrial
byproducts like fly ash blast furnace slag and silica fume,
it's usually cheaper to produce less clinker, so the use of
supplementary cementitious materials is already widespread
in the cement industry. One problem with this is that the
road to net zero in other industries is likely to limit
our access to many of those materials. Fly ash is a
byproduct of coal and blast furnace slag is a byproduct of
blast furnaces in steelmaking. As coal usage goes down and the
steel industry moves away from blast furnaces, availability of
those materials is going to dwindle, meaning that there are
going to be some limitations on this method going forward. But
there are other materials that can be used to replace these
substances, which we're not making much use of right now. A
company called Terra CO2 has developed a technique for using
silicate based igneous rocks. Calcined clay is another
possible alternative and a Danish company called Futurecem
has developed a method of combining calcined clay and
limestone to replace 40% of clinker in cement.
Now, using less cement and less clinker in that cement will help
to reduce the amount of CO2 released from turning limestone
into lime. But what if we were able to avoid that process
altogether? Limestone is the most common type of rock used in
cement manufacturing, but it's not the only one that can be
used. A US startup called Brimstone has developed a method
that they claim produces no process emissions creating
cement from calcium silicate rock, the final product is
chemically identical to Portland cement. But because there's no
carbon in the source mineral, there's no CO2 produced, they
have reportedly produced a small amount of zero emission Portland
cement from this method for the first time in 2022. And there's
another US startup called Sublime who are working on low
temperature processes to either start from limestone and capture
the CO2 from that reaction, or to take calcium out of different
minerals, and so avoid producing any CO2 at all. So those are
both very interesting, especially because it should be
possible to combine one of those processes with CO2 injection
like Carbon Cure is doing, in which case, you would end up
with carbon negative cement. But given that in both cases, it's
still very young technology. It's a bit too early to say for
sure if this production method will be able to scale up to the
level required by 2050.
If we can't get rid of all the emissions, we could still get to
zero emissions by either preventing the CO2 released from
escaping or by trapping an equivalent amount of CO2 from
somewhere else. There are a few technologies that can use cement
to permanently store carbon dioxide that's been removed from
the atmosphere. We already mentioned Carbon Cure, who
inject CO2 into concrete. Then other options include Mineral
Carbonation, which I covered in this video when I visited MCI
International and magnesium based cements, which can absorb
carbon dioxide over time, allowing us to use them as a
carbon sink. And finally, there's carbon capture and
storage (CCS). Put simply, carbon capture works by grabbing
and concentrating CO2 emissions from point sources like a coal
power plant or a cement factory and then storing it underground,
so it never makes it into the atmosphere. When it comes to
something like a coal power plant. This doesn't really make
any sense because it's far cheaper and more reliable to
simply get rid of the coal power plant and replace them with
renewable electricity generation and storage. When it comes to
cement though carbon capture may be our only choice. If we aren't
able to scale cement production from non carbon sources, carbon
capture may be the only way to deal with process emissions from
cement making it the industry where carbon capture is likely
to be the most essential to net zero transition. Carbon capture
is already in use in a number of cement plants worldwide.
Collectively, these plants captured about 100,000 tons of
CO2 in 2021, which may sound like a lot until you remember
that cement is responsible for two and a half billion tons of
CO2 each year, a lot of scale up would be needed to even make a
dent in global emissions from cement. And so far scaling up
CCS is something that has stumbled along making very
little progress for decades now. The scale of carbon capture
required reinforces why using less clinker in our cement as
well as using less cement overall is going to be
important. Getting rid of cement emissions is just really hard.
So those are all technologies with the potential to remove
process emissions but that still leaves emissions from heat. On
that front there are a few options available. Finland based
VTT has launched a project to develop electric kilns for
cement making. In early 2022, they were able to produce
clinker without fossil fuels for the first time with plans to
scale up the project over time. Two other projects. Heliogen in
the US and Solpart in France are attempting to get the energy for
the kiln directly from concentrating solar sunlight.
Both have reported achieving temperatures exceeding 1000
degrees Celsius so far, so we're getting close. So those are the
technologies available to get rid of emissions from cement out
a few of them together and zero emission cement is within reach.
Though, I really need to add the caveat that we are certainly not
close to a time when those technologies come at the same
price as traditional cement. So this is one instance where the
technology on its own is not going to be enough to eliminate
emissions it'll need to be combined with policies to
promote fast adaptation
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Thanks for watching, and I'll see you in the next video!