Concrete is the gray glue that binds our cities and industries together. It makes tall buildings possible and foundations strong. It helps us bridge rivers and valleys and keeps wind turbines upright. We don’t have a replacement for it. It’s not going anywhere.
But it’s also one of the largest sources of CO2 emissions globally, with estimates ranging from 5% to 12% depending on the source. The common solutions today for emissions are just like putting a little hydrogen in a natural gas line, an inadequate response to the climate crisis.
So what can we do about it? Do we have actual solutions? What will they cost? When will they be in place?
The greenhouse gas emissions from concrete come from a couple of major things and a few minor things. Let’s deal with the minor ones first, because they have obvious solutions.
Concrete is a mixture of cement — the glue — and fine and coarse gravel, typically referred to as aggregate, and sometimes replaced with non-gravel substitutes. Most of concrete’s CO2 emissions come from the manufacturing of cement.
Cement requires quicklime, which is manufactured from limestone (the hard bit to be covered next), clay and sand. These are all heavy materials which have to be mined and shipped, both of which use fossil fuels right now. And then the heavy cement has to be trucked to its point of use, using more fossil fuels. Electrification of mining equipment and transportation is under way, as is decarbonization of the grid. That part is just a matter of time. It’s only about 10% of the emissions challenge.
However, the process of making cement isn’t a fully solved problem right now, specifically the manufacturing of quicklime…