The production of cement is a major source of CO2 into the atmosphere. Various estimates put concrete production as responsible for a bit more than 5% of all CO2 emissions. While driving over the high concrete span over the Duwamish River in Seattle I got a glimpse of Seattle's single biggest CO2 source, Ash Grove's Seattle cement plant.
Cement plant from the West Seattle Bridge
Cement is inherently a big releaser of CO2. The chemistry is simple CaCO3 (calcite) + heat --> CaO (lime) + CO2. Hard to get around that CO2 source for what has been a basic building material for a very long time. I should add that there are some significant nuances in that other elements are then added to make say Portland cement such that the final product CO2 emission will vary depending on the specific concrete product.
As noted above, my view of this CO2 source was provided by a fair bit of concrete ifrastucture. In addition to the chemical reaction, turning limestone (calcite) into lime and CO2 requires a lot of heat. And hence, cement production often utilizes coal in the production of heat for the reaction. The tops of a couple of a coal piles can be seen at the cement plant in the image above and in the this areal view of the Ash Cement site.
Ash Cement site on Seattle's Duwamish River
Coal for kiln heat is on the left portion of site next to river
The primary limestone and coal source for the cement production is form Texada Island located between Vancouver Island and the mainland of British Columbia. The limestone is mined on Texada and coal is mined from an underground high BTU coal deposit on Vancouver Island not far from Texada Island.
Close up of Texada Island shipping terminal
All in all a fairly efficient operation. Ash Concrete has a position statement regarding greenhouse gases and regulatory mechanism HERE. While Ash (as of 2009) is not convinced anthropogenic CO2 will have a significant impact on climate change that will harm humans (perhaps nuance versus flat out denial), they take a position that a carbon tax would be preferable to a cap and trade scheme approach. It is an interesting read to get an industrial perspective with more than just a fossil fuel burning component.