There is specific focus on the roles of carbon dioxide (CO2) and methane (CH4) emissions and their effects on the atmosphere. Carbon dioxide has a significant impact on global warming partly because of its abundance in the atmosphere. Concrete has been the target of much criticism as a source of CO2 emissions. Much of this criticism reflects a lack of understanding of the difference between cement and concrete as a building product.

What is the true impact of CO2 emissions from concrete within the built environment? We can determine emissions from the cement manufacturing process with a high degree of accuracy. In contrast, there is much uncertainty as to the amount of carbon sequestration related to concrete over its life cycle.

A recent study (Xi et al: Substantial global carbon uptake by cement carbonation) indicates that 43% of all CO2 process emissions from production of cement over the period from 1930 to 2013 have been sequestered in concrete, not including emissions associated with fossil fuel use during cement production. This process is known as carbonation, or the reuptake of CO2 by concrete as a considerable carbon sink.

Understanding the carbonation process within concrete and its effect on Life Cycle Assessment (LCA) is indispensable to define concrete emissions and its true environmental impact. To better understand the effects of greenhouse gases associated with the built environment, a focused study on CO2 uptake in concrete within the context of the overall LCA is necessary. More inclusive environmental emission calculations are required to avoid misunderstanding concrete’s true environmental impact.

Not incorporating CO2 uptake by concrete into the overall LCA process, leads to an overestimation of net CO2 emissions. Given the massive scale of cement production and concrete use on a global scale, the level of CO2 uptake through carbonation is truly significant.

Click on the title of this paper to read and download a copy of the CalPortland research compilation entitled “Incorporating the Effect of Carbonation in Concrete Life Cycle Assessment” from this website.