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Cement may not be as environmentally damaging as thought

Carbon emissions from cement production could be almost 50 per cent less than previously thought, according to new research published in Nature Geoscience.

According to the research 43 per cent of the carbon emissions released from the production of cement between 1930 and 2013 has been offset by the process of “carbonation”, where cement products absorb carbon dioxide from the atmosphere.

The researchers say it is an important discovery as cement production accounts for approximately five per cent of all emissions from fossil fuel combustion and industrial processes, mainly through the process of calcination, which releases carbon dioxide into the atmosphere during cement production.

Harvard University physicist Dr Zhu Liu and colleagues used new and existing data on cement characteristics to mathematically model the amount of CO2 sequestered globally by four different cement materials during service life, demolition and secondary use.

They estimated that 4.5 gigatons of carbon were sequestered between 1930 and 2013, equivalent to 43 per cent of the CO2 emitted from calcination during that period. This makes cement a “substantial carbon sink”, according to the researchers. Fossil fuels used in the production of cement were not included, however.

The paper said that while civil engineers were well aware of carbonation reactions, due to the effects on strength and safety, the carbon sequestering properties had not been taken into account.

The researchers suggest that “future emissions inventories and carbon budgets may be improved by including this cement sink”.

While cement doesn’t have the carbon sequestering benefits of wood (and the carbon in wood also doesn’t affect structural properties), it’s still reassuring news that our buildings may not be as environmentally unfriendly as previously thought.

Comments

8 Responses to “Cement may not be as environmentally damaging as thought”

  • Michele R says:

    I think we have created some new vernacular with this article …”CO2 wash”!

  • Matt Williams says:

    Good to see Will Nash and Matthew calling this out for what it is, Greenwash! How can the study not consider the carbon impact of 50% of its footprint?! (fossil fuels in cement kilns). Whilst Portland Cement can’t be eliminated overnight there are plenty of viable alternatives out there but, unlike the inroads renewables are finally making into coal fired power generation, there are understandable apprehensions (and downright obsfucations) in moving away from the safe and known design considerations of conventional concrete. I hope we keep applying the pressure though and start using materials in a smarter way informed by LCA and the like.

  • Will Nash says:

    From the paper: “Demolition causes an increase in carbonation rates by exposing large and fresh surfaces. Because the average 35-year service lifetime of structures in China is shorter than the average 65–70 years in the US and Europe, the turnover of cement with respect to carbonation has been increasing over time, accelerating the uptake of CO2”

    By extension the authors are saying that shorter lifecycle buildings have helped sequester more CO2. This seems blinkered to the increased total CO2 emissions from cement manufacture.

  • John Blair says:

    Cameron: a quick check on Google Scholar does not reveal the article you’re referring to.

    Could you send me a full reference please?

    Many thanks – John Blair

  • Will Nash says:

    Greenwashing indeed – carbonation of cement causes corrosion of the steel and premature failure of the concrete. So the concrete that has absorbed the CO2 has to be replaced… by fresh concrete!

    Who funded this research?

  • Matthew says:

    “Fossil fuels used in the production of cement were not included, however.”

    This smacks of greenwash.

  • Alan Pears says:

    This is good news but thee process CO2 is only about half of the total CO2 from cement production – so this may be around 25% ‘credit’ but it comes over time, while the emissions associated with production are upfront. Given our need for urgent action, that delay in absorption matters over the next couple of decades. Also, for many reinforced steel structures, the emissions from steel used are comparable with the total emissions from the cement, so steel reinforced concrete is a much bigger emitter than the cement alone. And a lot of cement and steel is used simply to hold up heavy structures themselves, not deliver useful services…..

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