This is the Guardian.

In the race to half global emissions by 2030, there's a big blocky behemoth standing in the way.

Concrete. It's the most widely used substance on the planet after water. We make about 4 billion tons of it a year.

Concrete is strong and durable, which is why it's the

basis for so much of our infrastructure, but it's also terrible for the planet and

that's down to one key ingredient.

Concrete is a mixture of four things, cement, sand, stones and water, but cement is the ingredient that creates the bond and it's

also the driver of all the emissions in the material.

If the cement industry was a country

it would be the third largest producer of CO2 emissions

in the world after the US and China.

It's causing about 7.5% of all the world's CO2 emissions, so it's a really

massive driver of global warming. Bringing down the cost of our favourite building material has so far proved to be tricky.

But a new discovery, which the researchers have described as an absolute miracle could change all that, paving the way for a more

sustainable approach to construction.

So today we're asking, what is it that makes cement so damaging?

And is it time we got smarter about how we build?

From the Guardian, I'm Madeline Finley and this is Science Weekly.

Julian Allwood, your professor of engineering and the environment at the University of Cambridge,

and you've been leading a team of researchers who have come up with a way to recycle cement. So perhaps you can explain to me why you would

want to do that. Why is cement such an unsustainable material?

For two reasons.

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