Embodied Carbon in Concrete: Problems of Mis-Messaging

Is trade body information accurate about the embodied carbon in concrete?

Alice Moncaster (Open University) introduces new research that examines trade body information: Embodied Carbon of Concrete in Buildings, Part 2: Are the Messages Accurate? The claims made about thermal mass, durability and carbonisation are found to be at significant variance with the scientific literature. This has important implications for the messages it sends to construction professionals, decisionmakers and policymakers.

In the last few months COP26 and the IPCC Sixth Assessment Report have made it clear that our world is in a grave situation. Without rapid and substantial reductions in our greenhouse gas (GHG) emissions, many areas will soon become uninhabitable, by humans and most other forms of life. In other words, it’s too late to make incremental changes. Civil society needs to radically reassess what we do, and how we do it.

Embodied carbon

This is true for the construction sector more than most sectors. UNEP (2021) reports that global construction is directly responsible for 20% of energy-related GHG emissions, 10% of which is embodied in the materials of new buildings. Furthermore, a hefty chunk of total anthropogenic GHG emissions (8%) comes from the production of one construction material: cement. Cement is carbon intensive not only because of the high processing heat (and therefore fossil fuels) needed which accounts for 4% of total anthropogenic emissions, but also because CO₂ is released in a chemical reaction during the manufacturing process which adds an additional 4% (Olivier et al. 2016). Indeed the raw material for cement, limestone, is recognized by the Global Carbon Budget as a fossil reserve, thereby placing the calculation of GHG emissions from cement in the same category as those from oil and gas.

Despite all the evidence of harm, however, cement production is on the rise and predicted to grow further with increasing development.

There are plenty of other materials that buildings could be and are constructed from. Previous commentaries in this journal have pointed out that concrete wasn’t used in the past (Pender 2022) and doesn’t have to be now (Bardhan & Debnath 2022; Dodoo et al. 2022). So why do designers continue to specify concrete as a building material?

There are clearly a number of reasons. Established practices and knowledge, supply chains, and perceptions of risk are all factors.  There is also, still, a lack of understanding of how crucial embodied carbon is to climate change. For two decades European legislation has focused on the operational impacts of buildings from heating and lighting, rather than on the impacts from the construction materials. In the majority of EU countries there is still no legislation requiring the measurement of embodied carbon, although some countries are now providing leadership. There is also insufficient transparency and availability of comparable data for designers, contractors and decision makers.

Messages rather than measurements?

In the absence of measurement and regulation, the trade bodies representing the different construction materials play an important role in educating – or persuading – designers and specifiers about which product to use and its consequences.

The influence of marketing messages on consumer behaviour is not news to most of us.  What is perhaps less apparent is that designers and contractors are also ‘consumers’. Marketing messages by trade interests affect their thinking and decisions concerning the choice of materials and products.  

The concrete industry, with a major share of the construction market and significant funding, is particularly strong on such messaging. Our paper (Moncaster et al. 2022) showed that the main trade body for the cement and concrete industry in the UK, the Materials Products Association (MPA), repeatedly promotes three mechanisms through which it claims carbon emissions are reduced. The MPA suggests these mechanisms - thermal mass, durability, and carbonation –are sufficient to reduce the whole life carbon impacts of buildings by a very significant amount. These messages recur in much of their technical guidance, as well as in the roadmap to ‘beyond net zero’, and were repeated most recently in the MPA’s 2021 response to the UK Government Environmental Audit Committee Inquiry (MPA 2021).

The reduction in whole life carbon due to ‘thermal mass’ is shown in the report ‘Whole life carbon and buildings’ (MPA 2016) for example. Although no percentages are offered, a diagram suggests that thermal mass has the equivalent effect of reducing embodied carbon emissions by around a quarter. In the Roadmap to ‘beyond net zero’ (MPA 2020) thermal mass has an ‘emissions reduction potential’ of 44%. The 2016 report also proposes that the durability of concrete leads both to reduced maintenance and the reuse of concrete frames, which it shows reducing whole life emissions of buildings by again around a quarter. Finally, carbonation, the process by which exposed concrete slowly reabsorbs carbon over its lifetime, is again suggested in the 2016 report to reduce emissions by something similar a quarter, and shown to have an emissions reduction potential of 12% in the Roadmap.

Our research presented in Moncaster et al. (2022) demonstrates that, rather than these significant impacts, each of these mechanisms has at best a very limited effect on the whole life carbon of UK buildings.

First of all, for the vast majority of UK buildings there is slim evidence to support the idea that the thermal mass of concrete will significantly reduce operational carbon emissions. Even the MPA admits that thermal mass reduces cooling energy loads rather than heating (although this is frequently confounded). There is currently very little energy used on cooling in the UK. This is likely to rise under increasing global temperatures, but cooling technologies are powered by electricity, which is rapidly being decarbonised, and by on-site renewable resources. Even a significant increase in requirements for cooling is therefore likely to have very little increase in carbon emissions; we suggest no more than 2.5%, nowhere close to the 44% proposed by the Roadmap.

Secondly, the durability argument. Research shows that buildings tend to be demolished for reasons of economic growth rather than structural obsolescence.  There is no evidence that concrete framed buildings are more likely to be retained and reused than any other structural form, or that they are more durable.  On the other hand within the UK and elsewhere there is plenty of evidence for the durability of other materials, with several million buildings (including around 5 million homes) which are over 100 years old and are constructed of brick, timber and stone.

Finally, carbonation. This might be better termed ‘re-carbonation’, as it is the partial reabsorption of CO₂ originally released during the manufacturing process. For concrete used in buildings our research has demonstrated that there is much less carbonation than the MPA publications suggest – perhaps around 4% of the whole life emissions - with the majority happening after the building is demolished. Avoiding this initial release of CO₂ is clearly a better approach than hoping that some of it will be reabsorbed after the eventual end of life of the building, many years in the future.

Conclusions

The MPA itself concludes in their written evidence to the Environmental Audit Committee (MPA 2021):

‘all construction materials have an environmental impact and a carbon footprint, and they should be judged on the basis of facts rather than perception.’

Quite so. Until regulation is put in place to measure embodied impacts, designers and builders need to be able to base their decisions on verifiable facts about the likely impacts of using specific materials. The effect of messages from trade bodies on such decisions is difficult to ascertain but is potentially very significant. Therefore trade bodies like the MPA should not be making claims that cannot be supported. The research community and professional organisations also have a responsibility to monitor and review such claims and correct them where necessary. Our research has scrutinised some of the messaging around the use of cement and concrete in buildings, and we hope will lead to more clarity over the whole life carbon impacts.

References

Bardhan, R. & Debnath, R. (2022). Embodied carbon: breaking construction dependencies. Buildings and Cities [commentary] https://www.buildingsandcities.org/insights/commentaries/embodied-carbon.html

Dodoo, A., Dorn, M., Olsson, A. & Bader, T. (2022). Cross-laminated timber is a promising low-carbon structural solution. Buildings and Cities [commentary] https://www.buildingsandcities.org/insights/commentaries/clt-buildings.html

Moncaster, A., Malmqvist, T., Forman, T., Pomponi, F. & Anderson, J. (2022). Embodied carbon of concrete in buildings, Part 2: are the messages accurate? Buildings and Cities, 3(1), 334–355. http://doi.org/10.5334/bc.199

MPA. (2016). Whole life carbon and buildings: Concrete solutions for reducing embodied and operational CO2. London: Mineral Products Association (MPA) https://www.concretecentre.com/Publications-Software/Publications/Whole-life-Carbon-and-Buildings.aspx

MPA. (2020). Roadmap to beyond net zero. London: Mineral Products Association (MPA).https://www.mineralproducts.org/MPA/media/root/Publications/2020/MPA-UKC-Roadmap-to-Beyond-Net-Zero_Oct20.pdf

MPA. (2021). MPA UK Concrete submission. Environmental Audit Committee Inquiry on Sustainability of the Built Environment. https://committees.parliament.uk/writtenevidence/36093/pdf/

Olivier, J., Janssens-Maenhout, G., Muntean, M. & Peters, J. (2016). Trends in global CO2 emissions: 2016 report. The Hague: PBL Netherlands Environmental Assessment Agency. https://www.pbl.nl/sites/default/files/downloads/pbl-2016-trends-in-global-co2-emisions-2016-report-2315_4.pdf

Pender, R. (2022). Building without concrete? Buildings and Cities [commentary] https://www.buildingsandcities.org/insights/commentaries/building-without-concrete.html

UNEP. (2021). 2021 Global Status Report for Buildings and Construction: Towards a Zero-emission, Efficient and Resilient Buildings and Construction Sector.  Nairobi: United Nations Environment Programme (UNEP). https://www.unep.org/resources/report/2021-global-status-report-buildings-and-construction

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