Neutralizing the Downsides of Concrete

Concrete is a popular building material for good reason. It’s strong and durable, and it can be used as a finish as well as a structural material, reducing the need for other products.

But there’s a big drawback to concrete: its carbon footprint. Or, to be more precise, the carbon footprint of the binder used to make it—Portland cement. Portland cement emits tons of greenhouse gases (almost one ton for every ton of cement produced, in fact) for two reasons. First, it takes a lot of energy to make Portland cement. Limestone and other materials such as sand and iron are heated to 2,700ºF (1,480ºC) in massive cement kilns, and burning fossil fuels to fire these kilns emits about half the greenhouse gas emissions of Portland cement. The other half of its emissions come from limestone’s chemical conversion during the process, which releases CO2 directly into the environment. (Although coal was once the predominant fuel in cement kilns, alternative fuels and more efficient processes can be used to lower emissions.)