Note: This is an update to our previous analysis of CO₂-injected concrete, conducted in February 2025. After reviewing additional scientific literature and new information on the registry, we have revised our understanding of how natural carbonation and injected CO₂ interact. We have also updated our assessment accordingly. 

Calyx Global conducted our first credit rating from a concrete project under VM0043. This methodology accounts for over 99% of the credits currently on the market. Such projects have significant potential. After all, the world uses more than 30 billion tons of concrete annually for buildings, bridges, infrastructure and other applications. Global cement manufacturing, which produces the primary ingredient in concrete, resulted in 1.5 billion tons of CO2 emissions in 2024, generating 4% of the world’s CO2 emissions. 

Injection technology can reduce emissions by around 5% 

These projects deliver emission reductions because they allow producers to use less cement (a fossil-fuel-intensive input). Other efforts in the sector led to a 2.8% reduction in emissions last year[1]. If adopted throughout the world, this methodology could almost double the rate of emission reduction in this difficult-to-abate sector.

While CO2 injection can actually result in lower costs, and several government initiatives encourage the adoption of low-CO2 concrete, the technology is still nascent and barriers to adoption persist. Until the approach is more mature, carbon finance can play an important role in promoting the adoption of this technology. 

These projects deliver emission reductions and removals 

Because VM0043 features the injection of CO2 into the concrete mix, projects have the potential to deliver removals. However, our research shows that the removals are limited. Cement, the binding agent in concrete, begins to take up CO2 as soon as it is poured in a process called ‘carbonation.’ The injection of CO2 adds to the removals that would occur naturally; removals from the injection are the equivalent of 6 months-worth of the natural carbonation that will continue for the lifetime of concrete (up to 100 years). 

However, the methodology results in over-crediting 

The natural carbonation of cement negates between 18 and 68% of the emissions associated with concrete production over the lifetime of the concrete[2][3][4][5][6][7]. These natural ‘removals’ of CO2 from the atmosphere offset emissions from the fossil fuels used to produce cement. As a result, the net emissions are about 33% lower than they appear to be if only fossil fuel emissions are counted. Although natural carbonation is included in global emissions accounting such as the annual update by the Global Carbon Project, VM0043 does not account for it. As a result, baseline emissions are substantially overestimated. 

Rightsizing could provide a ‘fix’. Because this project type can justify its additionality due to the low uptake of the technology at present and it has no risk of non-permanence, over-crediting can be addressed by recalculating the number of credits generated. We call this rightsizing and believe this can be a useful approach when methodologies allow over-crediting. 

Conclusion

Tackling concrete is important. It is one of the hardest-to-abate sectors. Most of the emissions come from processing cement. Managing these emissions will require scaling up carbon capture, which is currently cost-prohibitive in most instances. There are a few options to avoid the use of cement, but also many applications where there are currently no alternatives. Total cement production is expected to grow rapidly in the coming years. Therefore, progress in this sector is critical and this project type – if it measures actual emission reductions well – can contribute to reducing global emissions.

Follow us on LinkedIn to keep up with our ongoing series on carbon removals. Next up: “The state of GHG quality of removal-based carbon projects.”

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[1] Friedlingstein et al. (2024). Global Carbon Budget 2024. Accessible at: https://essd.copernicus.org/preprints/essd-2024-519/

[2] Guo et al. (2021). Global CO2 uptake by cement from 1930 to 2019. Accessible at: https://essd.copernicus.org/articles/13/1791/2021/essd-13-1791-2021.html

[3] Xi et al. (2016). Substantial global carbon uptake by cement carbonation. Accessible at: https://www.nature.com/articles/ngeo2840

[4] Huang, Z., Wang, J., Bing, L., Qiu, Y., Guo, R., Yu, Y., ... & Liu, Z. (2023). Global carbon uptake of cement carbonation accounts 1930–2021. Earth System Science Data, 15(11), 4947-4958.

[5] Jungclaus, M. A., Williams, S. L., Arehart, J., & Srubar, W. (2024). Whole-life carbon emissions of concrete mixtures considering maximum CO2 sequestration via carbonation. Resources, Conservation and Recycling. https://doi.org/10.1016/j.resconrec.2024.107605

[6] Niu, L., Wu, S., Andrew, R. M., Shao, Z., Wang, J., & Xi, F. (2025). Global and national CO2 uptake by cement carbonation from 1928 to 2024. Earth System Science Data, 17(5), 2231-2247.

[7] Patrisia, Y., Law, D. W., & Zhang, J. (2025). Quantifying concrete recarbonation potential: A life cycle approach to carbon uptake. Environmental Impact Assessment Review. https://doi.org/10.1016/j.eiar.2025.108300