[Image above] Credit: Pavel Neznanov, Unsplash
With global demand for cement continuing to rise, there is a similarly increasing focus on the material’s carbon footprint. As such, players in the cement and concrete sectors are working diligently to achieve a reduction in emissions, such as by adopting new processing methods and laying out clear guidelines and regulations for the industry.
Estimating the impact of these measures on emissions is challenging, however, because there are multiple gaps in knowledge about the extent of these emissions. In other words, the industry lacks a firm baseline to compare the new initiatives against.
There are both social and technical reasons for these gaps.
On the social side, embodied carbon, or the emissions that come from the creation, maintenance, and disposal of building materials, has historically been considered insignificant compared with operational carbon, or the emissions that come from the ongoing operation of a building.
Research into and industry concern about embodied carbon have grown in recent years. But complexities of and variations in the data for the embodied carbon of concrete mean that conclusions remain nebulous.
For example, there are potentially infinite formulations for concrete, depending on the type and proportions of cement and aggregates; the addition of admixtures and plasticizers; and the specific manufacturers’ plants, processes, and fuels. So, there is not a single value for the carbon footprint of concrete that can be used in calculations.
Filling this knowledge gap will require an extensive curation and comparison of the hundreds of life cycle analyses out there for various cements, aggregates, and concrete mixes. Only then can the flaws in specific methodologies be identified, and manufacturers can develop a list of detailed rules for analyses that allow consistency to be maintained across different reports.
A group of researchers from several universities in the United Kingdom have taken it upon themselves to perform this monumental task. They are led by Open University visiting professor Alice Moncaster and Ph.D. student Jane Anderson.
With so much information to gather and analyze, the researchers plan to report their results over the course of three papers. The first open-access paper published in June 2020, and the second open-access paper published in May 2022. The third and final paper has not yet been published.
The first paper focused on reviewing and analyzing the several hundred available verified Environmental Product Declarations (EPD) that have been published for different cements, aggregates, admixtures, and ready-mix concretes.
EPD reports tell the life cycle story of a product in a single, comprehensive report. They are based on the life cycle assessment tool that follows ISO series 14040. These reports are typically less than 50 pages long, and they are available from The International EPD System database.
Based on the information in the EPD reports, the researchers created a series of detailed graphs and charts that they say will prove useful to three stakeholder groups.
- For building designers, the graphs will enable them to choose an appropriate value for the carbon footprint of concrete during early-stage calculations, which “can have an impact on major decisions on structural materials.”
- For building specifiers, the graphs will enable them to compare different products and choose those with lower impacts for the same performance requirements.
- For manufacturers, the graphs will enable them to compare their products with others, which will prompt competition and encourage minimization of impacts.
During data collection, the researchers found several inconsistencies or errors within the EPDs, which they reported to the manufacturers.
“…some errors were corrected and the EPD reissued by the EPD programs,” the researchers write.
The second paper, rather than focusing on the science of embodied carbon, focused on the messaging used to communicate about the carbon implications of concrete in buildings.
The researchers explain that they focused on the messaging because “Without mainstream uptake of detailed LCA [life cycle assessment] calculations, or of regulation, it seems likely that messaging can play a powerful role in influencing designers’ perceptions and decisions.”
Using the U.K. as a bounded case study, the researchers assessed the scientific accuracy of three common claims that appear in reports available on the concrete trade organization Mineral Products Association’s website. Specifically, the claims that high thermal mass, increased durability, and absorption of CO2 through carbonation are effective mechanisms through which concrete helps to reduce carbon emissions (compared to other building materials).
The researchers searched the scientific literature for studies done on these claims. Using the results from these papers, they determined that the absolute maximum reduction in whole-life carbon emissions from these three mechanisms would be under 9%, and for most buildings under 4%.
“The carbon impact of these mechanisms will therefore be a fraction of what [the Mineral Products Association’s report ‘Whole-life Carbon and Buildings’] suggests,” they write.
The researchers note that while this study focused on messaging in the U.K., these claims are not unique to that country.
“For example, in the Swedish context the cement industry highlights existing concrete structures as a carbon sink, stating in their Road-Map for a Climate-Neutral Concrete Construction that 15–20% of the calcination process emissions in the cement production is reabsorbed in existing concrete structures,” they write.
The researchers end the paper with a set of recommendations to improve the consistency and accuracy of reporting in the cement and concrete industry.
“More accuracy is needed … if real carbon reductions are to be achieved,” they write.
A future CTT will cover the third and final paper if and when it is published.
The 2020 open-access paper, published in Buildings & Cities, is “Embodied carbon of concrete in buildings, Part 1: analysis of published EPD” (DOI: 10.5334/bc.59)
The 2022 open-access paper, published in Buildings & Cities, is “Embodied carbon of concrete in buildings, Part 2: are the messages accurate?” (DOI: 10.5334/bc.199)