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  • Thousands of years ago, the Romans invented a material

  • that allowed them to build much of their sprawling civilization.

  • Pliny the Elder praised an imposing sea wall made from the stuff

  • asimpregnable to the waves and every day stronger.”

  • He was right: much of this construction still stands,

  • having survived millennia of battering by environmental forces

  • that would topple modern buildings.

  • Today, our roads, sidewalks, bridges, and skyscrapers

  • are made of a similar, though less durable, material called concrete.

  • There's three tons of it for every person on Earth.

  • And over the next 40 years, we'll use enough of it

  • to build the equivalent of New York City every single month.

  • Concrete has shaped our skylines,

  • but that's not the only way it's changed our world.

  • It's also played a surprisingly large role in rising global temperatures

  • over the last century,

  • a trend that has already changed the world,

  • and threatens to even more drastically in the coming decades.

  • To be fair to concrete, basically everything humanity does

  • contributes to the greenhouse gas emissions that cause global warming.

  • Most of those emissions come from industrial processes

  • we often aren't aware of, but touch every aspect of our lives.

  • Look around your home.

  • Refrigerationalong with other heating and cooling

  • makes up about 6% of total emissions.

  • Agriculture, which produces our food, accounts for 18%.

  • Electricity is responsible for 27%.

  • Walk outside, and the cars zipping past, planes overhead,

  • trains ferrying commuters to work

  • transportation, including shipping,

  • contributes 16% of greenhouse gas emissions.

  • Even before we use any of these things, making them produces emissions

  • a lot of emissions.

  • Making materials

  • concrete, steel, plastic, glass, aluminum and everything else

  • accounts for 31% of greenhouse gas emissions.

  • Concrete alone is responsible for 8% of all carbon emissions worldwide.

  • And it's much more difficult to reduce the emissions from concrete

  • than from other building materials.

  • The problem is cement, one of the four ingredients in concrete.

  • It holds the other three ingredientsgravel, sand, and watertogether.

  • Unfortunately, it's impossible to make cement without generating carbon dioxide.

  • The essential ingredient in cement is calcium oxide, CaO.

  • We get that calcium oxide from limestone,

  • which is mostly made of calcium carbonate: CaCO3.

  • We extract CaO from CaCO3 by heating limestone.

  • What's left is CO2— carbon dioxide.

  • So for every ton of cement we produce, we release one ton of carbon dioxide.

  • As tricky as this problem is,

  • it means concrete could help us change the world a third time:

  • by eliminating greenhouse gas emissions and stabilizing our climate.

  • Right now, there's no 100% clean concrete,

  • but there are some great ideas to help us get there.

  • Cement manufacturing also produces greenhouse gas emissions

  • by burning fossil fuels to heat the limestone.

  • Heating the limestone with clean electricity or alternative fuels instead

  • would eliminate those emissions.

  • For the carbon dioxide from the limestone itself,

  • our best bet is carbon capture:

  • specifically, capturing the carbon right where it's produced,

  • before it enters the atmosphere.

  • Devices that do this already exist,

  • but they aren't widely used because there's no economic incentive.

  • Transporting and then storing the captured carbon can be expensive.

  • To solve these problems,

  • one company has found a way to store captured CO2 permanently

  • in the concrete itself.

  • Other innovators are tinkering with the fundamental chemistry of concrete.

  • Some are investigating ways to reduce emissions

  • by decreasing the cement in concrete.

  • Still others have been working to uncover and replicate

  • the secrets of Roman concrete.

  • They found that Pliny's remark is literally true.

  • The Romans used volcanic ash in their cement.

  • When the ash interacted with seawater, the seawater strengthened it

  • making their concrete stronger and more long-lasting than any we use today.

  • By adding these findings to an arsenal of modern innovations,

  • hopefully we can replicate their success

  • both by making long lasting structures,

  • and ensuring our descendants can admire them thousands of years from now.

Thousands of years ago, the Romans invented a material

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B2 TED-Ed concrete cement carbon limestone greenhouse gas

The material that could change the world... for a third time

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    林宜悉 posted on 2021/03/01
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