A concrete idea to reduce CO2 emissions Karen Scrivener
Transcriber: TED Translators Admin
Reviewer: Mirjana Čutura
Concrete is the second
most used substance on earth after water,
and for this reason,
it has a significant environmental impact.
If it were a country, it would rank third
for emissions after China and USA.
But in fact, concrete
is an intrinsically low-impact material
with much lower emissions
of CO2 and energy per ton
than other materials like iron and steel,
even things like bricks.
But because of the enormous
volumes we use overall,
it contributes to about eight percent
of man-made CO2 emissions.
Concrete is an essential material.
We need it to house people,
to build roads, bridges and dams.
So we can’t do without it,
but we can significantly reduce
its carbon footprint.
Concrete is held together by cement.
And cement we use today,
called Portland cement,
is made by heating together a combination
of limestone and clay
at a temperature of 1,450 degrees Celsius.
But in fact, most of the CO2 emissions
come not from the heating,
but from the breakdown of limestone,
which is calcium carbonate,
into calcium oxide
and carbon dioxide, or CO2.
Now we can’t do without
this component altogether,
because nothing else is so efficient
at holding stuff together.
But we can replace
a large proportion of it
with other materials
with lighter carbon footprints.
Many colleagues are looking for solutions.
And here in Switzerland,
we have found that clays produce
very reactive materials
when they’re calcined,
that’s to say heated
to around 800 degrees Celsius,
significantly lower than the 1,450
needed to produce cement.
But more importantly,
there’s no CO2 emissions
from the decomposition of limestone.
We then take this calcined clay,
and we add a bit of limestone –
but this time not heated,
so no CO2 emissions –
and some cement,
and this combination of limestone,
calcined clay and cement, we call LC3.
Now this LC3 here
has the same properties
as Portland cement.
It can be produced
with the same equipment and processes
and used in the same way,
but has up to 40 percent
lower CO2 emissions.
And this was demonstrated in this house
we built near Jhansi in India,
where we could save
more than 15 tons of CO2,
which was 30 to 40 percent
compared to existing materials.
So why isn’t everybody already using LC3?
Well, cement is a local material.
The reason Portland cement is so pervasive
is that it’s produced
from the most abundant materials on Earth
and can be produced in India,
in the United States,
in Ethiopia, almost anywhere.
And we have to work with people locally
to find the best combination
of materials to make LC3.
We have already done
full-scale trials in India and Cuba.
In Colombia, a product
based on this technology
was commercialized a few months ago,
and in the Ivory Coast,
the full-scale plant
is being commissioned to calcine clays.
And many of the world’s
largest cement companies
are looking to introduce this
in some of their plants soon.
So the possibility to replace
Portland cement
with a different material –
but with the same properties,
produced in the same processes
and used in the same way,
but with much lighter carbon footprint –
is really crucial
to confront climate change
because it can be done fast
and it can be done on a very large scale
with the possibility to eliminate
more than 400 million tons
of CO2 every year.
So we can’t do without concrete,
but we can do without a significant amount
of the emissions it produces.
Thank you.