Using recycled carbon was a no-brainer to Gaurav Sant, the civil engineer who leads the UCLA team. The key binding ingredient in concrete is cement, which has a massive carbon footprint. The cement industry accounts for approximately 8% of global CO₂emissions, and if it were a country, it would be the world’s third-largest emitter.

Cement is made by heating limestone with other elements. About half of cement-related emissions come from the energy needed to run kilns at scorching temperatures, and these emissions could be avoided by switching to renewable power. But the other half is given off during chemical reactions involving limestone and can’t simply be eliminated.

So Sant and his team set to work on a greener approach that starts with a compound called portlandite instead of traditional Portland cement.

The production of portlandite also releases CO2. But its unique chemistry allows it to absorb CO2 later in the process, when the concrete cures and hardens into precast blocks and other shapes.

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