Carbon-storing building materials

In plain language

Concrete is made from cement, water, sand and gravel. Making cement releases CO2, both from the fuel burned and from the chemical change in the limestone. Builders are therefore looking for ways to cut the amount of cement, or to store carbon inside the product itself. Any change has to keep the concrete strong and durable, so a new material is only useful if it still does its job.

Two approaches are often grouped under this heading, and they work differently. Biochar is a carbon-rich solid made by heating plant material with little oxygen. Researchers have added it to concrete mixes in place of some sand or cement. Carbonation curing works the other way round. Fresh cement-based products are exposed to CO2 in a controlled chamber, so that the gas reacts to form solid carbonate minerals. Neither approach has yet shown, on its own, that a building product removes carbon from the air over its whole life.

Technical explanation

Biochar concrete uses pyrolysed biomass as a partial replacement for fine aggregate or cement. Biochar is porous and absorbs water, so its effect on workability, strength, shrinkage and durability depends on its feedstock, pyrolysis temperature, particle size and surface chemistry. A 2023 study by Roychand and colleagues reports that pyrolysed spent coffee grounds can be used to enhance concrete strength (Roychand and colleagues, 2023). The full text was not accessed, so no figures from it are cited here. Results from one biochar do not transfer to others.

A 2025 study by Roychand and colleagues evaluates coffee-biochar concrete in real-world construction (Roychand and colleagues, 2025). The full text was not accessed, so the details of the field trial are not cited here. Carbonation curing is a separate route. Zhang and colleagues (2025) describe a pilot-scale study of carbonation curing for bendable concrete, aimed at CO2 utilisation in infrastructure. Zou and colleagues (2025) study encapsulated biochar combined with carbonation in aggregate and concrete, using experiments and simulation. The full text was not accessed, so its results are not cited.

For climate claims, the functional unit matters. A candidate mix should be compared with a control that provides the same strength, stiffness, service life and maintenance needs, using cradle-to-grave accounting. That accounting must cover feedstock and its alternative uses, pyrolysis or CO2 capture and purification, curing energy, transport, use, and end-of-life handling such as crushing and recycling, because carbon can be released again at those stages.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The field evidence reviewed so far is limited to individual projects. The sources reviewed do not establish durability across climates, exposure conditions or structural applications.
• Biochar properties vary with feedstock and production conditions, so results for coffee-ground biochar cannot be generalised to other biochars without testing.
• A laboratory recipe may not repeat in commercial biochar production, so results from laboratory mixes need checking at scale.
• Carbon content does not automatically mean a net climate benefit. Alternative uses of the feedstock, pyrolysis energy and carbon release at end of life all affect the result.
• CO2 curing needs a reliable CO2 source, purification and transport, and it uses energy. The amount of CO2 supplied is not necessarily the amount stored, and CO2 taken from a fossil source may only delay its release.
• Building codes, procurement rules and environmental product declarations are built around established materials, so new mixes need specifications, fire and structural data, and service-life evidence before wide use.

Possible future uses

Product concepts: Carbon-curing cement blocks

Timeline

1. Sept 2023Laboratory study on spent coffee grounds as a concrete ingredient, reporting enhanced concrete strength, is published in the Journal of Cleaner Production. Sources: [4]
2. Feb 2025Pilot-scale study of carbonation-cured bendable concrete is published in the Journal of Cleaner Production. Sources: [2]
3. May 2025Study of encapsulated biochar and carbonation in aggregate and concrete, combining experiment and simulation, is published in Cement and Concrete Composites. Sources: [3]
4. Jul 2025Study of coffee-biochar concrete evaluated in real-world construction is published in Case Studies in Construction Materials. Sources: [1]

Futures this could help bring about

How far away?

Buildings that lock away carbon

Pilots · 2 of 6 steps done

Glossary

Biochar

Carbon-rich solid made by heating biomass with limited oxygen. Its properties depend on the feedstock and production conditions.

Carbonation curing

Controlled exposure of fresh cement-based material to CO2, so that carbonate minerals form in the product.

Functional unit

A defined service, such as a stated load capacity over a stated lifetime, used to compare the environmental impact of products fairly.

Sources

1. peer reviewed paper
   Translating lab success to the field: Evaluating coffee biochar-enhanced concrete in real-world construction
   Rajeev Roychand, Shannon Kilmartin-Lynch, Mohammad Saberian et al.. Case Studies in Construction Materials, Jul 2025. DOI: 10.1016/j.cscm.2025.e04233. Accessed 21 Oct 2026.
2. peer reviewed paper
   Pilot-scale validation of CO2 utilization for greener and tougher infrastructure through carbonation curing of bendable concrete
   Duo Zhang, Bing Feng, Beata Jaworska et al.. Journal of Cleaner Production, Feb 2025. DOI: 10.1016/j.jclepro.2025.144845. Accessed 21 Oct 2026.
3. peer reviewed paper
   Carbon sequestration in aggregate and concrete by encapsulated biochar and carbonation: Experiment and simulation
   Shuai Zou, Xi Chen, Man Lung Sham et al.. Cement and Concrete Composites, May 2025. DOI: 10.1016/j.cemconcomp.2025.105990. Accessed 21 Oct 2026.
4. peer reviewed paper
   Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength
   Rajeev Roychand, Shannon Kilmartin-Lynch, Mohammad Saberian et al.. Journal of Cleaner Production, Sept 2023. DOI: 10.1016/j.jclepro.2023.138205. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.