Reducing the Carbon Emissions of Concrete

Introduction

Concrete is the most widely used construction material worldwide. It is primarily composed of cement, water, sand, and gravel. The production of Portland cement, a key ingredient in concrete, is responsible for 1.6 billion metric tonnes of carbon dioxide (CO2), or about 8% of global CO2 emissions. Innovations in reducing the carbon footprint of concrete are critical to addressing climate change.

Strategies to Reduce Carbon in Concrete

• Use of Supplementary Cementitious Materials (SCMs): Incorporating SCMs such as fly ash, slag, silica fume, biochar, and calcined clay can reduce the amount of cement required, thus lowering carbon emissions.

• Carbon capture and storage (CCS): Technologies that capture and store CO2 emissions from cement plants can substantially reduce carbon output.

Alternative Binders

• Geopolymers: Utilizing industrial by-products to create geopolymer binders can cut CO2 emissions by up to 80% compared to traditional Portland cement (Abbas, et al.,2024, Srinivasan and Sivakumar, 2013, Rajamane et al., 2014)

• Calcium Silicate Cements (CSCs): These alternatives can absorb CO2 during curing, partially offsetting emissions from production (Wang, et al. 2022).

Use of Recycled Materials

• Incorporating recycled and innovative course aggregates (e.g. iron and steel slags, sintered fly ash lightweight aggregates) and fine aggregates (e.g. Manufactured Sand, copper slag, granulated blast furnace slag, foundry waste sand) reduces the need for virgin materials, thereby decreasing environmental impact (Subramanian, 2019, IS 383:2016).

• Recycling concrete from demolished structures as aggregate in new construction conserves resources and reduces waste.

Efficient Design and Construction Techniques

• Optimization:?Effective structural design can minimize material use and result in significant reductions in concrete and subsequent CO2 emissions.

• 3D Printing: Advanced construction technologies like 3D printing use only the necessary amount of material, reducing waste and emissions. But, we should note that 3D-printed concrete may emit more CO2 than normal concrete.
• Scientists at Nanyang Technological University, Singapore (NTU Singapore) have developed a 3D concrete printing method that captures carbon, demonstrating a new pathway to reduce the environmental impact of the construction industry. The innovative method, detailed in Ref. 3, aims to significantly reduce the carbon footprint of cement – through lower material usage, reduced construction time, and labor requirements. Results have shown that the method of injecting steam and CO2 improved the mechanical properties of the concrete, offering increased strength compared to conventional 3D-printed concrete.

The Role of Policy and Regulation

• Governments can promote low-carbon concrete by setting regulations that encourage or mandate the use of environmentally friendly materials and technologies.

• Tax incentives for sustainable construction practices can accelerate the adoption of greener concrete solutions.

Case Studies and Innovations

• Projects like The Edge in Amsterdam demonstrate the use of low-carbon concrete in high-performance, sustainable building design (see the Photo at the top).
• The Edge Building demonstrates sustainable and ecological design with maximum impact. With a record score of 98.36% from the BREEAM, it is considered the most sustainable and ecological building in the world. Designed and built by PLP Architecture, its focus on energy efficiency incorporates innovative technologies, such as solar panels to generate electricity and thermal energy storage. In addition, it offers comfort to workers through remote control of temperature and lighting through their mobile phones. It reuses rainwater for green areas and has received recognition for its inspiring architectural approach.

• Startups are developing new concrete technologies that incorporate CO2 directly into the concrete mix, transforming it into a part of the material.
• For Example, CarbonCure’s equipment is retrofitted into concrete plants. The CarbonCure Valve Box is connected to the CO? tank stored onsite and automatically injects a precise dosage of CO? into the concrete during mixing.?The CarbonCure Control Box syncs with the plant’s batching software, so adding CO??to a mix is as easy and quick as flipping a switch.

Challenges and Considerations

• Performance requirements of alternative cement are still being investigated to meet long-term durability and structural integrity standards.

• Economic impacts, including cost considerations and market acceptance, can play crucial roles in the widespread adoption of low-carbon concrete.

Future Outlook

• With continued innovation and adoption of sustainable technologies the construction industry can significantly mitigate its environmental impact.

• Collaborative efforts among engineers, policymakers, and researchers are key to advancing carbon reduction in concrete construction.

References

1. Abbas, R., Abdelzaher, M. A., Shehata, N., and Tantawy M A (2024) "Production, characterization and performance of green geopolymer modified with industrial by-products" Sci Rep., Mar., 1;14:5104. doi: 10.1038/s41598-024-55494-8
2. https://natural-resources.canada.ca/funding-partnerships/co2-utilization-concrete-new-circular-economy-model
3. https://genexigente.com/el-edificio-sostenible-the-edge-amsterdam-destaca-como-referente-arquitectonico/
4. IS 383:2016, Course and Fine Aggregates for Concrete-Specification, Bureau of Indian Standards, New Delhi, 18 pp.
5. Lim, S.G., Tay, Y.W.D., Paul, S.C., Lee, J., Amr, I.T., Fadhel, B.A. Jamal, A., Al-Khowaiter, A.O., and Tan, M.J. (2024) "Carbon capture and sequestration with in-situ CO2 and steam integrated 3D concrete printing", Carbon Capture Science & Technology, Vol.13, Dec., 100306
6. Rajamane N.P., M.C. Nataraja and R. Jeyalakshmi (2014) “Pozzolanic industrial waste based geopolymer concretes with low carbon footprint”, The Indian Concrete Journal, Vol. 88, No 7, July, pp. 49-68.
7. Srinivasan, K., and Sivakumar, A. (2013)Geopolymer Binders: A Need for Future Concrete Construction, ISRN Polymer Science,https://doi.org/10.1155/2013/509185
8. Subramanian, N. (2019)Building Materials-Testing and Sustainability, Oxford University Press, New Delhi, 788 pp.
9. Wang, X., Guo, M.-Z. and Ling,T.-C. (2022)"Review on CO2 curing of non-hydraulic calcium silicates cements: Mechanism, carbonation and performance",n Concrete Journal, Vol. 88, No 7, July, pp. 49-68.
10. Srinivasan, K., and Sivakumar, A. (2013)Geopolymer Binders: A Need for Future Concrete Construction, ISRN Polymer Science,https://doi.org/10.1155/2013/509185
11. Subramanian, N. (2019)Building Materials-Testing and Sustainability, Oxford University Press, New Delhi, 788 pp.
12. Wang, X., Guo, M.-Z. and Ling,T.-C. (2022)"Review on CO2 curing of non-hydraulic calcium silicates cements: Mechanism, carbonation and performance", Cement and Concrete Composites, Vol. 133, Oct. 104641 https://doi.org/10.1016/j.cemconcomp.2022.104641

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