New Cement Might Make for Carbon-Negative Concrete

Concrete is responsible for about 5% to 8% of the world’s anthropogenic carbon emissions, and that is largely due to the binder that holds it together, portland cement. So creating a low-carbon concrete that does not use portland cement is the green building industry’s holy grail. One manufacturer claims it has ended the quest.

Portland cement’s double carbon whammy

The problem with portland cement comes down to its manufacturing process. Making it requires heating limestone (calcium carbonate) to temperatures that eventually reach 2,700ºF (1,480ºC). This calcination process creates lime (calcium oxide) and eventually portland cement. This chemical change is also responsible for most of its CO2 emissions. The kiln’s energy consumption then adds to overall greenhouse gas emissions. Hence its overall high global warming potential (GWP)—a median carbon intensity of about three-quarters of a ton of emissions for every ton of cement produced in the U.S., according to the U.S. Environmental Protection Agency.