Can building materials store carbon?

What these materials are

Concrete is a mix of cement, water, sand and gravel. Carbon-storing building materials are products designed to keep carbon in solid form rather than let it return to the air. One possible route is to store carbon inside the product itself, provided the concrete stays strong and durable enough to do its job.

Two approaches are grouped under this heading, and they work differently. The first adds biochar, a carbon-rich solid, to the mix. The second cures cement-based products with carbon dioxide (CO2), so that the material takes up the gas as it sets.

How carbon gets into the material

In the biochar approach, the carbon is already part of the solid when it is mixed in. In a 2023 laboratory study, Roychand and colleagues heated spent coffee grounds at 350 °C and 500 °C, then used the grounds to replace part of the fine aggregate (sand) in concrete (Roychand and colleagues, 2023).

Carbonation curing works differently. The cement-based product is exposed to CO2 during curing, and the cement takes up the gas. The 2025 pilot study by Zhang and colleagues expresses this as CO2 uptake relative to the mass of cement (Zhang and colleagues, 2025).

What has been demonstrated

The results below were measured in the studies, although each is tied to a specific mix, feedstock or site.

Carbonation-cured bendable concrete. Zhang and colleagues tested carbonation curing of engineered cementitious composites, also called bendable concrete, at pilot scale. Total CO2 uptake fell from 26.6% to 4.3% of cement mass as specimen thickness increased. The team cast non-reinforced slabs from carbonated material and installed them in a sidewalk renovation in Southeast Michigan. The slabs had a heavily carbonated surface over a nearly non-carbonated core. Even so, the slabs' flexural strength improved by 31.7%, with a high intensity of fine cracks maintained. The authors report only a marginal loss of strength and ductility over 3 years, and the slabs remained intact after 34 months in service (Zhang and colleagues, 2025).

Coffee-ground biochar in the laboratory. In the 2023 study, raw and pyrolysed coffee grounds replaced 5, 10, 15 and 20% of the fine aggregate by volume. Organic compounds leaching from the raw grounds hindered cement hydration and significantly reduced compressive strength. Grounds pyrolysed at 350 °C gave a 29.3% increase in the compressive strength of the blended concrete (Roychand and colleagues, 2023).

A real construction project. A 2025 study by Roychand and colleagues evaluated coffee-biochar concrete in real-world construction, working with a local council. The team tested slump, compressive strength of the concrete and of cored slab samples, flexural strength and shrinkage against a control mix. The authors conclude that it has potential as a sustainable construction material, but that supply-chain limitations must be addressed before it becomes a mainstream material (Roychand and colleagues, 2025).

What is only reported

The items in this section are authors' claims or titles that we could not check against full results.

Encapsulated biochar with carbonation. Zou and colleagues study carbon sequestration in aggregate and concrete using encapsulated biochar and carbonation, through experiment and simulation. The bibliographic record has no abstract, so we give no figures from the paper (Zou and colleagues, 2025).

Field-trial biochar. The 2025 field study reports that the commercial producer's pyrolysis equipment could not operate at the optimal 350 °C, so the biochar used on site was not made at the temperature that worked best in the laboratory (Roychand and colleagues, 2025).

Structural benefit as climate benefit. Zhang and colleagues argue that carbonation curing offers more emission reduction through stronger slabs, which could allow smaller structures and less cement, than through the CO2 taken up directly. They present this as a path towards low-carbon infrastructure (Zhang and colleagues, 2025). We treat this as the authors' argument, not a measured whole-life result.

We found no manufacturer carbon figures in the sources reviewed for this article.

What is speculative

Whether whole buildings could store large amounts of carbon is not tested by these sources. The studies examine specimens, slabs, aggregate and concrete mixes, and field trials, not complete structures (Zhang and colleagues, 2025; Zou and colleagues, 2025). Any building-scale claim would need its own evidence.

Limits and open problems

How much carbon is stored. In the Michigan work, CO2 uptake fell as the specimen thickened, and the authors describe the slabs' capacity for CO2 storage as limited (Zhang and colleagues, 2025). Carbon held in a product is not the same as a net climate benefit, which would also need to account for things such as the energy used in production.

Biochar variability. The strength results cited here come from one feedstock, spent coffee grounds, pyrolysed at 350 °C and 500 °C. They do not show that other biochars would behave the same way (Roychand and colleagues, 2023).

Supply. The field project shows that a commercial producer may not be able to reproduce laboratory conditions (Roychand and colleagues, 2025).

Permanence and durability. The longest service record here is 34 months for the Michigan slabs. The evidence comes from individual projects and single sites, so it does not show how the materials would perform across different climates or in structural use (Zhang and colleagues, 2025; Roychand and colleagues, 2025).

Codes and cost. We found no source on building codes, standards or cost for these materials, so these questions remain open.

What to watch next

• The full results of the encapsulated-biochar study by Zou and colleagues, including any carbon figures.
• Follow-up data from the coffee-biochar field project, particularly durability over time.
• Longer service records for the Michigan carbonation-cured slabs, beyond 34 months.
• Whether biochar can be produced at commercial scale to the specifications the laboratory work used.