A newly developed method to recycle cement could yield a billion metric tons yearly by 2050, equivalent to about one-quarter of global annual production of this important building material, a new study suggests. What’s more, the method has the potential to achieve a holy grail of the green building industry: zero-emission cement.

The new study shows that large-scale cement recycling has practical potential says study team member Cyrille Dunant, an engineer at the University of Cambridge in the UK.

Cement is used to bind together sand, gravel, and water to make concrete. Concrete, in turn, is a foundation of global infrastructure: it’s the second-most-used material on the planet (behind only water).

Concrete is responsible for about 7.5% of global greenhouse gas emissions

Concrete is also responsible for about 7.5% of global greenhouse gas emissions, and is fiendishly difficult to decarbonize.

The climate problem with concrete pretty much comes down to cement. Nearly 90% of concrete emissions arise from the production of cement, which is made by crushing limestone and other materials and heating them to extremely high temperatures. This requires a lot of energy, and the consequent transformation of limestone into lime releases large amounts of carbon dioxide.

Nearly 90% of concrete emissions arise from the production of cement

Past efforts to shrink the carbon footprint of concrete production have focused on finding materials such as fly ash to substitute for cement. But such strategies still require some use of cement, and the alternative materials aren’t available in high enough volumes for the global industry: the strategy essentially tinkers around the edges of what remains a behemoth problem.

The new approach instead relies on an extremely abundant material: concrete itself. It is already possible to separate cement from the other ingredients of used concrete, but until now there has been little market for this recovered cement paste.

The spark for the new method came from the realization that recovered cement paste has a lot in common with lime flux, another carbon-intensive material made from limestone, which is floated on top of melted steel to remove impurities during steel recycling.

In conventional steel recycling, used lime flux results in a waste product called slag. The new method instead employs used cement to remove impurities in the steel, and results in recycled cement that can then be used to make new concrete.

“The performance of cement as a flux was much better than expected,” Dunant reports.

High temperatures during the steel recycling process “re-clinker” the cement, which refers to the reactivation of oxides that are key to its binding function. In a paper published in the journal Nature, Dunant and his collaborators describe using an electrically powered arc furnace, an apparatus that is already commonly used in steel recycling, to accomplish this process.

This is the second key takeaway of the study, Dunant, says: “clinker production can be electrified.” If the arc furnace is powered by renewable electricity, the result could be zero-emission cement.

If the arc furnace is powered by renewable electricity, the result could be zero-emission cement.

By reducing the need for lime flux, the new method also reduces the carbon emissions involved in recycling steel. What’s more, the method adds little to the cost of either concrete or steel.

The recycled cement contains a higher level of iron oxide than conventional cement, but this shouldn’t affect its performance, the researchers say.

Widely implementing the process will be far from straightforward. “It’s always difficult to do co-production, particularly on a large scale, so the commercial route still needs to be understood, and what trade-offs will be required ‘in the real world’ between steel and cement production are still unknown,” Dunant says.

Still, the findings suggest the heartening conclusion that sometimes the way to solve a difficult environmental problem is to tackle two at the same time.

Source: Dunant C.F. et al.  “Electric recycling of Portland cement at scale.” Nature 2024.

References:

1. Miller, S. A., Horvath, A. & Monteiro, P. J. Readily implementable techniques can cut annual CO₂ emissions from the production of concrete by over 20%. Environ. Res. Lett. 11, 074029 (2016).

   Article ADS Google Scholar

2. Friedlingstein, P. et al. Global carbon budget 2022. Earth Syst. Sci. Data 14, 4811–4900 (2022).

   Article ADS Google Scholar

3. Bajželj, B., Allwood, J. M. & Cullen, J. M. Designing climate change mitigation plans that add up. Environ. Sci. Technol.47, 8062–8069 (2013).

   Article ADS PubMed PubMed Central Google Scholar

4. Scrivener, K., Martirena, F., Bishnoi, S. & Maity, S. Calcined clay limestone cements (LC³). Cem. Concr. Res. 114, 49–56 (2018).

   Article CAS Google Scholar

5. Zunino, F. et al. Hydration and mixture design of calcined clay blended cements: review by the RILEM TC 282-CCL. Mater. Struct. 55, 234 (2022).

   Article CAS Google Scholar

6. Busch, P., Kendall, A., Murphy, C. W. & Miller, S. A. Literature review on policies to mitigate GHG emissions for cement and concrete. Resour. Conserv. Recycl.182, 106278 (2022).

   Article CAS Google Scholar

7. Turner, L. K. & Collins, F. G. Carbon dioxide equivalent (CO₂-e) emissions: a comparison between geopolymer and OPC cement concrete. Construct. Build. Mater. 43, 125–130 (2013).

   Article Google Scholar

8. Gartner, E. & Sui, T. Alternative cement clinkers. Cem. Concr. Res. 114, 27–39 (2018).

   Article CAS Google Scholar

9. Dunant, C. F., Drewniok, M. P., Orr, J. J. & Allwood, J. M. Good early stage design decisions can halve embodied CO₂ and lower structural frames’ cost. Structures 33, 343–354 (2021).

   Article Google Scholar

10. Allwood, J. M. & Cullen, J. M. Sustainable Materials: With Both Eyes Open (Univ. Cambridge, 2012).

11. Ma, J. et al. Carbon capture and storage: history and the road ahead. Engineering 14, 33–43 (2022).

    Article CAS Google Scholar

12. Ho, D. T. Carbon dioxide removal is not a current climate solution — we need to change the narrative. Nature 616, 9 (2023).

    Article ADS CAS PubMed Google Scholar

13. Hills, T. P., Sceats, M., Rennie, D. & Fennell, P. LEILAC: low cost CO₂ capture for the cement and lime industries. Energy Procedia 114, 6166–6170 (2017).

    Article CAS Google Scholar

14. Manocha, S. & Ponchon, F. Management of lime in steel. Metals 8, 686 (2018).

    Article Google Scholar

15. Snellings, R., De Schepper, M., De Buysser, K., Van Driessche, I. & De Belie, N. Clinkering reactions during firing of recyclable concrete. J. Am. Ceram. Soc.95, 1741–1749 (2012).

    Article CAS Google Scholar

16. Jawed, I. & Skalny, J. Alkalies in cement: a review I. Forms of alkalies and their effect on clinker formation. Cem. Concr. Res. 7, 719–729 (1977).

    Article CAS Google Scholar

17. Krour, H. et al. Incorporation rate of recycled aggregates in cement raw meals. Constr. Build. Mater. 248, 118217 (2020).

    Article CAS Google Scholar

18. Rodrigues, F., Carvalho, M. T., Evangelista, L. & de Brito, J. Physical–chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants. J. Clean. Prod. 52, 438–445 (2013).

    Article CAS Google Scholar

19. Guignot, S., Touzé, S., Von der Weid, F., Ménard, Y. & Villeneuve, J. Recycling construction and demolition wastes as building materials: a life cycle assessment. J. Ind. Ecol. 19, 1030–1043 (2015).

    Article CAS Google Scholar

20. Gao, X. X., Cyr, M., Multon, S. & Sellier, A. A three-step method for the recovery of aggregates from concrete. Constr. Build. Mater. 45, 262–269 (2013).

    Article Google Scholar

21. Carriço, A., Bogas, J. A., Hu, S., Real, S. & Costa Pereira, M. F. Novel separation process for obtaining recycled cement and high-quality recycled sand from waste hardened concrete. J. Clean. Prod. 309, 127375 (2021).

    Article Google Scholar

22. Prajapati, R., Gettu, R. & Singh, S. Thermomechanical beneficiation of recycled concrete aggregates (RCA). Constr. Build. Mater. 310, 125200 (2021).

    Article Google Scholar

23. Pato, N., Zajac, M. & Schmidt, V. M. Zementindustrie: Kreisläufe und kohlendioxid. Nachr. Chem. 70, 38–40 (2022).

    Article CAS Google Scholar

24. Zajac, M. et al. Effect of carbonated cement paste on composite cement hydration and performance. Cem. Concr. Res. 134, 106090 (2020).

    Article CAS Google Scholar

25. Florea, M. V. A., Ning, Z. & Brouwers, H. J. H. Smart Crushing of Concrete and Activation of Liberated Concrete Fines(Univ. Eindhoven, 2012).

26. Dunant, C. F., Allwood, J. M. & Horton, P. M. Process for the combined manufacture of steel and cement clinker (WO 2023/285678 A1). ZKG Cement Lime Gypsum Issue 2 (2023).

27. EN, British Standard: BS EN 197-1:2011 cement. Composition, specifications and conformity criteria for common cements (incorporating corrigenda November 2011, October 2015 and February 2019) (European Committee for Standardisation, 2011).

28. Maciejewski, J. The effects of sulfide inclusions on mechanical properties and failures of steel components. J. Fail. Anal. Prev. 15, 169–178 (2015).

    Article Google Scholar

29. Carette, J. & Staquet, S. Monitoring the setting process of mortars by ultrasonic P and S-wave transmission velocity measurement. Constr. Build. Mater. 94, 196–208 (2015).

    Article Google Scholar

30. Tsivilis, S. & Parissakis, G. A mathematical model for the prediction of cement strength. Cem. Concr. Res. 25, 9–14 (1995).

    Article CAS Google Scholar

31. Bishnoi, S., Maity, S., Mallik, A., Joseph, S. & Krishnan, S. Pilot scale manufacture of limestone calcined clay cement: the Indian experience. Ind. Concr. J. 88, 22–28 (2014).

    Google Scholar

32. Allwood, J. M., Dunant, C. F., Lupton, R. C. & Serrenho, A. C. H. Steel Arising: Opportunities for the UK in a Transforming Global Steel Industry (Univ. Cambridge, 2019).

33. Shanks, W. et al. How much cement can we do without? lessons from cement material flows in the UK. Resour. Conserv. Recycl. 141, 441–454 (2019).

    Article Google Scholar

34. Department for Environment, Food & Rural Affairs. UK Statistics on Waste(Department for Environment, Food & Rural Affairs, 2014).

35. Wang, J. et al. A bayesian approach for the modelling of material stocks and flows with incomplete data. Preprint at https://arxiv.org/abs/2211.06178 (2022).

36. Carriço, A., Bogas, J. A. & Guedes, M. Thermoactivated cementitious materials – a review. Constr. Build. Mater.250, 118873 (2020).

    Article Google Scholar

37. Snellings, R., Bazzoni, A. & Scrivener, K. The existence of amorphous phase in portland cements: physical factors affecting Rietveld quantitative phase analysis. Cem. Concr. Res. 59, 139–146 (2014).

    Article CAS Google Scholar