Portland cement is a material that holds together the sand and crushed stone in concrete.

VOA: special.2009.12.01

And so, when you think about how much cement concrete are consumed annually on the planet, this becomes a considerable point source of greenhouse gas emissions.

当你想到,在地球上每年要消耗多少的水泥混凝土的时候,这将是温室气体排放的,一个主要来源。

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The idea is to replace some of the portland cement traditionally used in making concrete.

VOA: special.2009.12.01

The Portland Cement Association says the gas from the limestone is reabsorbed as concrete ages.

VOA: special.2009.12.01