Could Biochar Replace Cement in the Concrete of the Future?

By Ankit SinghReviewed by Sarah KellyOct 30 2026

Concrete is the most widely used construction material on Earth, but its main binding agent, cement, carries a heavy climate cost. Cement production accounts for around 8% of global carbon emissions each year, largely due to heating limestone in kilns.¹ 

Image Credit: Yo_bie/Shutterstock.com

To mitigate this environmental impact, engineers have traditionally used materials such as fly ash or slag to reduce the carbon footprint of concrete. An emerging alternative is biochar, a carbonaceous material produced via pyrolysis of biomass in low-oxygen environments. Plants absorb CO₂ as they grow, so locking that carbon into char and then concrete could store it for decades.^1,2

This article examines the role of biochar in concrete, evaluates various feedstocks, assesses potential carbon savings, and identifies scenarios in which concrete performance may be compromised.^1,2

How Biochar Works Inside Concrete

Under a microscope, biochar resembles a rigid sponge filled with tiny pores. When these particles are mixed into cement paste, the finest ones

slip between cement grains and fill voids that would otherwise weaken the hardened material. Chemical groups on the char surface also attract nearby cement particles, drawing them into clusters where hydration products, the mineral glue of concrete, can form more densely.¹

These pores also retain water. When biochar is soaked before mixing, it slowly releases moisture as the concrete cures, a process known as internal curing. This steady supply of water helps the cement continue reacting deep within the material, which can reduce shrinkage and early cracking.^1,4

Some biochars also contain amorphous silica, which reacts with cement hydration byproducts to form additional binding compounds, similar to the volcanic ash used in ancient Roman concrete.¹

Moreover, the porous structure of biochar changes how heat and sound move through a wall. Ordinary concrete conducts heat efficiently through its paste and aggregate, and biochar interrupts those pathways. Studies report lower thermal conductivity, improved sound absorption, and stronger shielding against electromagnetic waves as the biochar content increases. The high surface area also provides CO₂ with additional sites to react with calcium, forming stable carbonate minerals during carbonation curing.¹

Feedstocks Under Testing

In principle, almost any organic matter can become biochar. Laboratories have tested rice husks, peanut shells, corn stalks, coconut shells, bamboo, sawdust, wood waste, food scraps, sewage sludge, and even animal manure.¹

Agricultural and forestry residues dominate the research because they are cheap, abundant, and often burned or landfilled. Woody feedstocks tend to yield char with higher carbon content and more developed pore networks.¹

The choice of feedstock shapes results in measurable ways. A meta-analysis of 606 paired observations found that most plant-based biochars raised 28-day compressive strength by 3% to 13%, although rice and hardwood char were exceptions. However, the strength benefits were less pronounced in mixes containing aggregates, highlighting the importance of concrete composition.³

Chars produced above 450 °C and ground to small particle sizes performed best. Sludge and industrial waste need to be screened first, since they can carry heavy metals into the final product.^1,3

Production conditions are just as crucial as the raw materials used. Slow pyrolysis, which gradually heats biomass to temperatures between 300 and 700 °C over one to two hours, promotes the formation of stable, high-yield char.¹

A study published in Springer Biochar tested 16 different biochars and used machine learning to identify the traits that best predicted mortar strength. Initial water saturation, oxygen-to-carbon ratio, and soluble silicon emerged as the three strongest factors.⁴

What Biochar Means for Carbon Emissions

The climate case rests on two synergistic effects. For every kilogram of biochar that replaces cement, the emissions associated with producing that cement are avoided. A recent life-cycle assessment published in RCR Advances estimated that this reduction is about 0.63 kg of CO₂ equivalent per kilogram, mainly due to calcination.⁵

The char also contains carbon that plants have absorbed from the atmosphere, potentially resulting in a negative carbon footprint.⁵

The numbers from the same assessment illustrate the scale. Replacing 20% of cement by volume with wood biochar reduced concrete emissions by 42%. Similarly, substituting 60% of sand with fruit-waste biochar resulted in a remarkable 101% reduction in emissions, allowing the concrete to sequester more carbon than was emitted during its production.⁵

The energy recovered from pyrolysis gases and oils further enhances these environmental benefits.⁵

Economic modeling supports these findings. A study reported in Springer Biochar found that a mix containing 30% biochar had a carbon footprint of 58 kg/ton, compared with 421 kg/ton for the control. Its estimated carbon tax benefit rose from about $2.60/m³ to $34.10/m³. Though promising, results like these do depend heavily on assumptions about transport, feedstock, and the counting of biogenic carbon.^1,5

Trade-Offs in Strength, Workability, and Fire Performance

Environmental gains unfortunately come at the expense of strength as biochar dosage increases, with some research indicating that strength improves when biochar is kept below 2.5% of binder weight, and other studies reporting such losses at replacement levels greater than 5%.^3,4

Less cement means fewer hydration products, and excess char particles clump into weak zones. Scientists have also noted that, with careful selection of biochar, a replacement level of up to 10% can be used in mortar formulations without compromising compressive strength.⁴

The porosity that improves concrete curing also complicates on-site mixing and placement. Biochar absorbs mixing water, which can reduce flowability by 10–18% at a 5% dosage, and often shortens setting times. Engineers can offset these effects by presoaking the biochar, adjusting its particle size, or adding water-reducing admixtures. Durability results are mixed, with sulfate resistance improving over weeks and declining in longer exposure tests.¹

High temperatures reveal how biochar’s role within the mix shapes its performance. A study published in Composites Part C tested concrete containing 10% to 20% biochar and found that strength declined gradually as biochar content increased.⁶

After heating to 600 °C, mixes using biochar in place of sand held their strength relative to the control. However, mixes that used biochar in place of cement only kept pace with the control up to 200 °C.⁶

Conclusion

Biochar works in concrete by filling voids, storing curing water, and providing additional surface area for mineral formation. Researchers have

tested a long list of agricultural, forestry, and urban wastes, and the best results come from carefully controlled pyrolysis.

Life-cycle studies show meaningful emissions reductions, and some mixes achieve net-negative footprints, especially when char replaces sand. However, delivering durability and fresh-mix behavior still requires considered design.⁵

Higher amounts of biochar lead to greater carbon savings but can also result in weaker concrete. Therefore, advancements depend on engineering biochars that maintain performance at higher doses. Standardized testing, a reliable feedstock supply, and transparent carbon accounting will determine whether biochar can transition from laboratory research to practical applications in construction.

If these elements align, concrete could effectively sequester carbon in buildings and roads for many decades.

References and Further Reading

1. Ye, P. et al. (2025). The state-of-the-art review on biochar as green additives in cementitious composites: performance, applications, machine learning predictions, and environmental and economic implications. Biochar, 7(21). DOI:10.1007/s42773-024-00423-1. https://link.springer.com/article/10.1007/s42773-024-00423-1
2. Room, S., & Bahadori-Jahromi, A. (2024). Biochar-Enhanced Carbon-Negative and Sustainable Cement Composites: A Scientometric Review. Sustainability, 16(23). DOI:10.3390/su162310162. https://www.mdpi.com/2071-1050/16/23/10162
3. Zhao, Z. et al. (2024). Biochar affects compressive strength of Portland cement composites: a meta-analysis. Biochar, 6(21). DOI:10.1007/s42773-024-00309-2. https://link.springer.com/article/10.1007/s42773-024-00309-2
4. Hylton, J. et al. (2024). Relevant biochar characteristics influencing compressive strength of biochar-cement mortars. Biochar, 6(87). DOI:10.1007/s42773-024-00375-6. https://link.springer.com/article/10.1007/s42773-024-00375-6
5. Wang, D. et al. (2026). Life cycle assessment of both cement and sand-replaced biochar concrete. RCR Advances, 30. DOI:10.1016/j.rcradv.2026.200337. https://www.sciencedirect.com/science/article/pii/S266737892600026X
6. Mensah, R. A. et al. (2024). Fire behaviour of biochar-based cementitious composites. Composites Part C: Open Access, 14. DOI:10.1016/j.jcomc.2024.100471. https://www.sciencedirect.com/science/article/pii/S2666682024000410

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.