Cut carbon dioxide from cement (CO2) emissions remained a challenge, despite widespread efforts to reduce CO emissions2 and save the planet from the worst climate change scenarios predicted by the scientific community. New research has highlighted a potential path to efficient carbon capture and use with an innovative approach using carbon mineralization.
Why cut CO cement2 Emissions Important?
Around the world, the demand for new buildings and infrastructure continues to increase, and therefore for concrete. While the ubiquitous building material causes relatively low mass emissions (less than 150 kg of CO2 per tonne of concrete), the sheer amount we use means it is responsible for up to 8% of human-caused CO2 emissions.
Latest Intergovernmental Panel on Climate Change (IPCC) report warns we need to achieve zero CO2 by 2050 – at a minimum – to avoid the worst-case scenarios of climate change. Tackling the major problem of concrete and CO2 emissions is therefore extremely important.
First and foremost, developers, planners, and citizens need to consider whether new buildings and infrastructure are needed. Reusing and restoring old buildings, maintaining and repairing buildings, and recycling building materials can all help reduce the total environmental damage of concrete by reducing the amount of new concrete produced.
Carbon mineralization to reduce CO in concrete2 Emissions
CO2 concrete emissions are mainly the result of cement manufacturing processes, with clinker production cited as the main cause.
To combat this, many researchers and cement producers have focused on reducing the amount of clinker needed for cement. Supplementary cementitious materials (SCM) are used to reduce the amount of clinker in the cement content. However, almost all SCMs adapted to meet the growing demand for concrete are already in use.
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In addition, concrete made with SCMs has limited applicability due to reduced mechanical strength. Specific applications such as precast concrete and high quality clay still require a high clinker content to be used safely.
Decreasing the clinker content also increases the risk of neutralization of the pore solution in the concrete. This, in turn, can lead to reinforcement corrosion due to carbonation.
Making clinker production more energy efficient is another method that has been pursued to reduce the amount of clinker produced. However, further improvements in energy efficiency can only be marginal, as the technology reaches the theoretical efficiency limit of clinker production.
In this context, the only way to make the cement less harmful is to capture the CO2 before it is emitted in the production of clinker. Carbon capture and use methods have the best potential to improve the impact of concrete on the environment. To effectively capture carbon emissions at the source, carbon mineralization techniques must be perfected and scaled up for industrial use.
Research on additional cementitious materials, carbon capture and use
A review of the literature recently criticized the construction industry’s reliance on DCS to reduce CO emissions2 emissions. He found several unanswered questions regarding the carbonation of concrete made with SCMs and criticized the extensive and almost exclusive use of SCMs in infrastructure development.
A recent research paper proposed a new approach to carbon capture and use that could overcome these problems. The carbonaceous mineralization of fines from recycled concrete has led to the production of new carbonatable materials and the reduction of net CO2 emissions. This article was published in the journal Scientific reports March 27, 2020.
The researchers stored the captured CO2 in calcium and magnesium carbonates. These do not easily dissolve in water, so the stored carbon will not be quickly returned to the hydrosphere. In fact, researchers have argued that these carbonates provide a permanent storage solution for CO2.
CO2 reacts with calcium or magnesium in rocks rich in alkaline earth silicates. In the natural world, silicate rocks like these react with CO2 over a geological period. Alteration effects of calcium and magnesium carbonates as well as silicon dioxide (SiO2).
Converting this process into an industrial technique for carbon capture and utilization is a challenge as the reaction has to be accelerated with mechanical, thermal or chemical treatments and carried out under extremely high pressure. In addition, large amounts of carbonatable material must be extracted and transported to the CO.2 carbonation plant.
When the CO2 has been captured, it must be used or disposed of effectively. The separation of calcium and magnesium carbonates improves the usability of carbonatable materials produced from carbon capture and utilization methods.
Researchers have found that these challenges are effectively addressed by using concrete fines – a byproduct of concrete recycling – as carbonatable materials. The researchers created a hydrated paste from concrete fines that could be carbonated with much less energy than silicate rocks.
The paste is mainly composed of calcite silica and alumina gels, which are very reactive. This means that carbon mineralization can take place within 28 days of hydration. Used as SCM, carbonate paste saves up to 114.5 g of CO2 for 100g of dough, more than a third of savings more than with a limestone SCM.
How can the cement industry benefit from this research and reduce CO2 Emissions?
Concrete fines are residual materials from recycling concrete that cannot yet be recovered. The method proposed in this research could be applied in the concrete industry to recover this waste while moving towards net zero CO.2 through carbon capture and use.
For this technology to be widely adopted, advances in concrete recycling must be made. Current technology does not properly separate coarse aggregates, sand and hydrated cement paste from recycled concrete.
Finally, for this method to reach its full potential, all of the CO2 emitted during the manufacture of concrete must be captured at the source of the pollution. It will only work if it is fully adopted and supported by the industry.
Industrial response to climate change
This article is part of the IPCC Editorial Series: Industrial Response to Climate Change, a collection of content exploring how different sectors are responding to the issues highlighted in the IPCC 2018 and 2021 reports. Here, Nano presents research institutions, industry organizations and innovative technologies leading to adaptive solutions to mitigate the climate change.
References and further reading
IPCC. (2018) Summary for policymakers. Global warming of 1.5 ° C. An IPCC special report on the impacts of global warming 1.5 ° C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat climate change, sustainable development and efforts to eradicate poverty. Available at: https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15_SPM_version_report_LR.pdf
IPCC. (2021) Summary for policymakers. Climate change 2021: the basis of physical science. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Available at: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf
Skocek, J., M. Zajac and M. Ben Haha (2020) Capture and use of carbon by mineralization of cement pastes derived from recycled concrete. Scientific reports. Available at: https://doi.org/10.1038/s41598-020-62503-z.
von Greve-Dierfeld, S. et al. (2020) Understanding the carbonation of concrete with additional cementitious materials: a critical review by RILEM TC 281-CCC. Materials and structures. Available at: https://doi.org/10.1617/s11527-020-01558-w.