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  • Hi, this is Alex from MinuteEarth, in a special collaboration with Bill and Melinda Gates.

  • Around the world, almost 7 million people move to, or are born in, cities every month.

  • Which can be super efficient, because when people live close to each other, it's easier

  • to move people, power, water, and basically everything else around.

  • But it's also a problem: in order to build all the buildings and infrastructure these

  • new city dwellers will need - the equivalent of a new New York City every single month

  • for the next 40 years - we're going to need a lot of concrete.

  • And for the health of the planet, concrete is a one-two punch.

  • Well, technically cement is the heavy hitter.

  • It's the thing that, y'know, cements the basic ingredients of concrete - sand, rocks

  • and water - together into a single, useful material, and it's a mean source of planet-warming

  • carbon dioxide.

  • Cement's one-two punch comes from how it's made.

  • First, we have to heat limestone - which typically requires us to use lots of fossil fuels, which

  • emit CO2.

  • Second, once we do that, the limestone chemically breaks down into lime, which goes into the

  • cement along with some other stuff, and carbon dioxide, which goes into the air.

  • In most industrial processes, the energy used to run machines and heat stuff up is the overwhelming

  • source of carbon dioxide, but with cement, when the limestone itself breaks down, it

  • releases even more CO2 than all the other parts put together.

  • All told, for every ton of cement we make, almost a ton of CO2 gets released.

  • Today, cement's double whammy leaves it responsible for 8% of humanity's carbon

  • dioxide emissions - that's more than airplanes, ships, and long distance trucking put together.

  • And as we keep on building a new New York City each month, the emissions from cement

  • are only going to go up.

  • So, what to do about cement?

  • We could build some of these new buildings out of other materials and we also could use

  • less cement per building.

  • For the cement we do use, we could try to manufacture and heat it using renewable sources.

  • And these things would certainly help!

  • But the real game-changer would be to stop using limestone itself in cement - then it

  • wouldn't release CO2 when it breaks down.

  • And there actually are alternatives out there already, some of which can reduce the amount

  • of limestone needed - and others that can replace limestone completely.

  • So far, most of these alternatives are either too expensive to make or too early in development

  • or are being adopted tentatively because concrete is such an important structural material.

  • But some alternative cements are already being used successfully in major buildings and bridges

  • around the world, and when we use cement with less limestone, or with no limestone at all,

  • as the foundation for all of our new cities, we'll reap some seriously concrete benefits.

  • This video was produced in collaboration with Bill and Melinda Gates, who every year write

  • a letter describing their philanthropic efforts.

  • In this year's letter, they discuss 9 surprising things they learned in 2018, and how those

  • surprises have prodded them into action.

  • In addition to being surprised by the rapid death of old-school textbooks and the fact

  • that toilets haven't changed in a century, they were also troubled by the environmental

  • impacts of global urbanization - and we were happy to help them explain one of the impacts

  • in a concrete way.

  • To read the letter yourself, click the link in the description or visit GatesLetter.com.

Hi, this is Alex from MinuteEarth, in a special collaboration with Bill and Melinda Gates.

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B1 中級 美國腔

混凝土的问题(The Problem With Concrete)

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    joey joey 發佈於 2021 年 04 月 30 日
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