Neutron Imaging Study Uncovers Water's Role in CO₂ Storage in Recycled Concrete

Neutron imaging research conducted by the Institut Laue-Langevin on July 9, 2026, reveals how water limits CO₂ storage in recycled concrete. The study highlights the potential of using concrete waste to capture carbon, addressing two pressing environmental issues: high CO₂ emissions from construction and concrete waste accumulation.

Understanding CO₂ Storage in Recycled Concrete

The construction sector is responsible for 5%–7% of global CO₂ emissions due to energy-intensive cement production and the release of CO₂ from limestone. Concrete waste poses another challenge, with billions of tonnes discarded annually during demolition. Accelerated carbonation offers a solution by allowing recycled concrete to capture CO₂, transforming it into stable mineral compounds.

Researchers at the ILL utilized neutron imaging to observe the interaction of water and CO₂ within cement paste during carbonation. This real-time analysis showed that carbonation alters the material's structure, affecting water release, pore networks, and CO₂ transport. Understanding these dynamics is crucial for developing effective carbonation treatments.

The Process of Accelerated Carbonation

Accelerated carbonation accelerates the natural reaction where CO₂ penetrates concrete and forms calcium carbonate. By exposing recycled concrete aggregates to CO₂-rich gas, the reaction can be expedited under controlled conditions. This process is particularly beneficial for recycled aggregates, which often retain old cement paste that is more reactive.

• CO₂ reacts with cement paste to form calcium carbonate.
• Old cement paste provides pathways for CO₂ entry.
• Too little or too much water can hinder the carbonation process.

The delicate balance of moisture and gas permeability is essential for effective carbonation. As the carbonation progresses, the material undergoes changes that can enhance or impede the process.

Implications for Sustainable Construction

Using recycled concrete for CO₂ capture presents a dual opportunity: reducing emissions and minimizing waste. The potential for reusing between 2.8 and 5.1 gigatonnes of concrete annually could significantly lower the construction sector's carbon footprint. This approach not only diverts waste from landfills but also decreases the demand for virgin aggregates.

By better understanding the interplay of CO₂, water, and mineral reactions, researchers aim to optimize accelerated carbonation processes. This could lead to more sustainable construction practices and a circular economy model, ultimately contributing to lower carbon emissions.