Storing CO2 in Concrete for Sustainable Construction
By: Prof. Don Mac Elroy | Director of Technology at NEG8 Carbon
Concrete is the second most-used substance in the world after water (sustainability.mit.edu) and construction and buildings have the infamous claim of contributing a hefty 37% of the 38 billion tonnes of CO₂e (CO2 equivalent) emitted globally each year (UN Environment Programme report (2023))
As efforts to tackle climate change intensify, smart ideas are emerging such as storing CO₂ in concrete, effectively turning buildings into carbon sinks.
A study led by Elisabeth Van Roijen at the University of California, Davis, explores how transforming traditional building materials into carbon-capturing alternatives could remove up to 16.6 billion tonnes of CO₂ annually, a remarkable figure. The results of the study were published in the journal Science (2025).
Two Key Strategies for Locking Carbon into Concrete
The first is altering the composition of concrete and bricks to include carbon-absorbing aggregates (Van Roijen et al. show that replacing traditional cement and concrete aggregates with CO2-storing materials could remove 13.1 billion tonnes of atmospheric CO2 annually).
The second is injecting captured CO₂ into wet concrete during its manufacture. Once the CO2 has been injected into the concrete, it reacts with the cement – with calcium (Ca) or magnesium (Mg) compounds – to form stable calcium carbonate, mimicking natural carbonisation in rocks but at a much faster pace.
Why Portland cement is bad for the environment
To make Portland cement, which is used extensively in concrete, limestone or chalk are heated with clay at an extremely high temperature (1450 °C) to make clinker, which is then ground to produce cement. Firing at this high temperature uses mostly fossil fuel energy which makes this process emissions intensive. This is then exacerbated by the CO2 emitted when heating limestone. In fact, one tonne of carbon dioxide is emitted for every tonne of cement produced.
Benefits of Trapping CO₂ in Concrete
Efficiency and Permanence
Between 85% and 94% of the injected CO₂ is absorbed in the concrete and secured for good.
Strength of Concrete
The chemical reactions not only lock in carbon but also improve the concrete’s durability.
Environmental Impact
With an annual global concrete production of 30 billion tonnes (and 4.25 billion tonnes of cement), the potential for a positive impact is enormous.
Although concrete’s weight-related carbon storage is relatively low, it is so widely used, which makes it an excellent carbon sink when implemented on a global scale.
For every cubic metre of concrete, about 13 kgs of CO₂ can be locked away. This process would help offset the 7%-8% of global emissions attributed to cement production. Also, and more importantly, emissions are lower because about 5% less cement is used resulting in approximately 10% CO₂ less net emissions from cement utilization.
The technology to inject CO₂ into concrete already exists and is starting to gain traction. For example, it is simple to retrofit a valve box to a CO₂ storage tank which can then inject the required amount of CO₂ into the concrete as it mixes. Another option is to install a CO₂ canister to a concrete mixer truck which administers the exact amount of CO₂ needed on the go.
The pertinent question is: “Where do you get the CO₂ from to add to the concrete?”
This is a valid question and for this process to really do the job of reducing CO₂ in the atmosphere and cut emissions, the CO₂ must be sourced using carbon capture technologies like Direct Air Capture.
The Role of Direct Air Capture (DAC) in Capturing CO2 for Environmentally Friendly Concrete
Direct Air Capture (See: How Does Direct Air Capture Work?) could play a major part in this vision by extracting CO₂ directly from the atmosphere at any location. The captured carbon dioxide can then be integrated into the building materials supply chain, ensuring a closed loop that removes CO₂ and stores it permanently.
This solution tackles the issue of providing sustainably sourced CO₂ for concrete while also addressing another question: what should be done with the CO2 captured via DAC? One option is to store the CO₂ underground in depleted oil and gas wells or via geological mineralisation. Another is to use it in a different process, as in this case. (See: What is CO2 Sequestration? and What is CO2 Utilization?)
Challenges of CO2 Sequestration in Concrete
While the concept is promising, challenges remain.
Supply chain issues around sourcing and transporting CO₂ at scale remain complex. However, advancements in technologies like Direct Air Capture have the potential to provide a consistent supply of CO2.
The building sector is traditionally risk averse. Introducing new materials may be met with resistance, particularly in applications with high structural demands. To mitigate these challenges, early applications of carbon-capturing materials might focus on non-structural uses, such as flooring, pavements, and insulation, where performance risks are lower.
Furthermore, there needs to be a system of monitoring and verification especially if the captured and stored CO2 is purchased to offset emissions.
Sustainable Concrete – Looking Ahead
Interest is certainly rising in this approach to carbon sequestration. For example, the U.S Department of Energy’s Office of Fossil Energy and Carbon Management recently announced $101 million in federal funding to support the development of CO2 capture, removal and conversion test centres for cement manufacturing and power plants.
The awarded projects include the Board of Trustees of the University of Illinois for the CO2 conversion technologies in the cement industry, and Holcim US, who plan to build a Cement Carbon Management Innovation Centre at its cement facility in Maryland.
Carbon-capturing materials present a compelling option for reducing global CO₂ emissions, particularly when scaled across industries as vast as construction.
For more:
- The Advantages of Direct Air Capture
- With Direct Air Capture, We Can Avoid €20bn in Emissions Fines
- NEG8 Carbon Nominated for Prestigious Earthshot Prize 2025
- Achieving Net-Zero Carbon Emissions Targets with Direct Air Capture