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  • 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.

Transcriber: TED Translators Admin Reviewer: Mirjana Čutura

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A concrete idea to reduce CO2 emissions | Karen Scrivener

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    林宜悉 posted on 2021/03/04
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