New Generation Green Material: Biochar Concrete

1.What is Biochar?

Biochar is a solid carbon material produced by biomass pyrolysis under oxygen-lacking/non-oxygen conditions. Its properties (surface area, pore structure, surface functional group, alkalinity, etc.) are strongly dependent on the pyrolysis temperature and the type of biomass, and these parameters determine the degree of "taste" with the cement binder [1], [2].

2.The process for making biochar

• Biomass preparation (drying, screening);
• Pyrolysis (~450–700 °C; heating rate/time/gas flow control);
• Safe cooling – dust/moisture control;
• Quality analysis (ash, pH, BET, pore distribution) [1], [2].

3.Why is biochar concrete considered a "new generation green material"?

Technical perspective. Biochar beads have a pore system – large surface area: (i) water retention and slow release → internal curing to reduce premature shrinkage; (ii) play the role of "filler-nucleation" to create hydrolysis germs, thicken the ITZ region; (iii) the combination of accelerated CO₂ curing (ACC) helps capture and mineralize CO₂, and can enhance early age if optimized [1]–[3].

Life Cycle Perspective (LCA). The recent LCA framework shows that a roadmap for partial replacement of cement with biochar and copper optimized with SCMs (fly ash, slag) is feasible to reduce emissions; The benefits depend on the biochar source, energy and the manufacturing-use scenario [4].

The process of making biochar concrete

Three common integration strategies [1], [2], [7], [8]:

• Partial replacement of cement (the starting point of practice is usually in low-medium doses): it is necessary to be superplastic, with priority given to fine particles to promote the "filler–nucleation" effect.
• Replace some of the sand/fine (aiming for internal curing and/or volume reduction): pre-saturate the biochar to stabilize the drop.
• Converted into a biochar-rich pellet or core-shell: dust-reduction/water absorption, easy to operate on an industrial scale, and carbon "lock" at the particle level [7], [8].

Learn more about the characteristics of biochar concrete.

  Mechanism of action in cement matrix

• Internal curing: biochar capillaries store water → prolong hydration, reduce micro-cracking due to premature shrinkage [1], [2].
• Filler–nucleation & ITZ: fine particles thicken microstructures, improve junction [1], [2].
• ACC: biochar (dry/presaturated) + CO₂ → increase CO₂ mineralization levels and can increase the intensity (depending on the pyrolysis temperature/dose/age) [3].

  "Safe" integration & distribution strategy

• Practical starting dose: change the cement at a low–medium level; change the sand by a few percent to activate internal curing; always test the slump-compression/bending -resistivity-absorbency on the target mix level [1], [2].
• Biochar treatment: fine grinding, pre-saturation, superplasticizing use; consider ACC when having carbon targets and sustainability [1]–[3].
• Industrial scale: CLWA or core–shell is preferred to improve repeatability, reduce operational risks, and facilitate logistics [7], [8].

  Mechanical & long-lasting features

• Mechanical: most of the data suggest retention/intensity at low–moderate doses (especially when fine-grained, presaturated, or ACC is present); high doses are easy to reduce intensity due to increased emptiness – water absorption [1], [2], [3].
• Cl⁻ & corrosion: the 2024 structural study (  dry–wet alternating CaCl₂ environment) emphasizes the need for moisture/nourishment management, as local moisture around the reinforcement can sensitize corrosion; mechanically, dry samples can increase the intensity [5].
• Freezing–thawing (F/T): durable F/T depends on biochar characteristics & dose; ≤ 5 % and fine particles may improve, high doses risk rapid mass loss during the F/T cycle—hence the need for mix-specific testing [6].

4. Comparison of biochar concrete with popular concrete today

Biochar concrete                                Concrete Current

Advantages:

• Reducing life cycle emissions: replacing part of cement with biochar, combined with SCMs (fly ash/slag) is a promising LCA roadmap; the added benefit of ACC integration [4], [3].
• Microstructure & long-lasting: internal curing + "filler–nucleation" reduces absorbency, supports ITZ microstructure, maintains/increases mechanics at optimal doses [1], [2].
• Industrial operation (granular solution): CLWA or core-shell for easy mixing – less dust – less water absorption; at the same time, it is a carbon storage tank at the aggregate level [7], [8].

Challenges

• Functionality: biochar reduces drop/increases water demand if not optimal (needs superplasticity/presaturation); high doses are easy to reduce intensity [1], [2].
• Corrosion in specific chloride environments: moisture control is required, especially under dry–wet CaCl₂ [5].
• Cold – humid area: durable F/T sensitive to size/pores/hydrophilic of biochar; requires F/T testing according to local standards [6].
• Standardization: there is currently no separate designation in EN/ACI; should be designed according to features and proven equivalent [1], [2].

Conclusion

Biochar concrete is not an "elixir" for all grades, but it is a feasible route to reduce emissions and optimize microstructures when deployed at the right dose – right process: fine grain/pre-saturated, superplasticity compatible, ACC consideration; in parallel, prioritize CLWA/core–shell particle configuration for scale production. In order to move towards widespread application, it is necessary to standardize biochar characterization – test methods, apply feature-based design and integrate LCA into distribution decisions [1]–[8].

References

[1] S. Barbhuiya, B. B. Das, and F. Kanavaris, “Biocharconcrete: A comprehensive review of properties, production and sustainability,” Case Studies in Construction Materials,vol. 20,e02859,2024. [Online]. Available: https://assets.syncraft.at/2024/10/PU-Barbhuiya-2024-Biochar-Concrete.pdf

[2] G. Murali and L. S. Wong, “A comprehensive review of biocharmodified concrete: Mechanical performance and microstructural insights,” Construction and Building Materials, vol. 425, 135986, 2024.  [Online]. Available: https://www.sciencedirect.com/science/article/pii/S0950061824011279?utm_source

[3] Y. Chen et al., “Accelerated carbonation curing of biocharcement mortar: Effects of biochar pyrolysis temperatures on carbon sequestration, mechanical properties and microstructure,” Construction and Building Materials, 2024. [Online].Available:https://www.sciencedirect.com/science/article/pii/S0950061824035888?utm_source

[4] “Circular economy for the building industry: Life cycle assessment of biochar in cementitious materials,” Resources, Conservation & Recycling, 2025 (online first). [Online].Available:https://www.sciencedirect.com/science/article/pii/S092134492500415X?utm_source

[5] F. Zanotto et al., “Study of the corrosion behaviour of reinforcing bars in biocharadded concrete under wet and dry exposure to calcium chloride solutions,” Construction and Building Materials, vol. 420, 135509, 2024. [Online].Available:https://www.sciencedirect.com/science/article/pii/S2352710225001950?utm_source

[6] T. Chen, Z. Yang, H. Liu, L. Li, L. Qin, and X. Gao, “Effect of biochar characteristics on freezethaw durability of biocharcement composites,” JournalofBuildingEngineering,111959,2025. [Online].Available:https://www.sciencedirect.com/science/article/pii/S2352710225001950?utm_source

[7] M. Wyrzykowski, N. Toropovs, F. Winnefeld, and P. Lura, “Coldbonded biocharrich lightweight aggregates for netzero concrete,” Journal of Cleaner Production,vol. 434,140008,2023. [Online].Available:https://www.sciencedirect.com/science/article/pii/S0959652623041665?utm_source

[8] S. Zou, M. L. Sham, J. Xiao, L. M. Leung, J.X. Lu, and C. S. Poon, “Biocharenabled carbonnegative aggregate designed by coreshell structure: A novel biochar utilising method in concrete,” Construction and Building Materials,138507,2024.Online].Available: https://www.sciencedirect.com/science/article/pii/S0950061824036493?utm_source

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