Each year, global cement production releases more than two and a half billion tonnes of CO₂ into the atmosphere. This immense carbon footprint makes concrete one of the biggest hurdles in the transition to a low-carbon economy. Now, researchers at Northwestern University have developed a technology that could help turn the tide: a carbon-negative building material that not only avoids emissions but also captures CO₂ from the air—while generating hydrogen as a valuable by-product. The method, which mimics the shell-forming process of molluscs, produces a new kind of sand that could form the foundation for greener concrete.
Producing sand for sustainable concrete—and clean energy
To create this innovative carbon-negative material, the researchers introduced electrodes into seawater and applied a low-voltage electric current. This current splits water molecules, releasing hydrogen and generating hydroxide ions. Simultaneously, COâ‚‚ is injected into the seawater, altering its chemical composition and increasing the concentration of bicarbonate ions.
These hydroxide and bicarbonate ions then react with other dissolved minerals naturally found in seawater, such as calcium and magnesium. The result is the formation of solid compounds—mainly calcium carbonate and magnesium hydroxide. Calcium carbonate acts as a direct carbon sink by locking away CO₂ in its crystal structure, while magnesium hydroxide can continue to absorb carbon through further chemical reactions.
According to the researchers, this approach resembles the way molluscs and corals form their shells, using biological energy to transform dissolved ions into calcium carbonate. In this case, the team has swapped biological energy for electricity and boosted mineral formation by adding COâ‚‚ to speed up the process.
Crucially, when powered by renewable energy, the system also produces green hydrogen as a by-product—a clean fuel with a growing role in sectors such as transport, chemicals and power generation. This dual benefit positions the technology as a tool not only for reducing emissions but also for generating renewable energy.
Reducing reliance on sand mining
As well as tapping into abundant natural resources, the technique offers an alternative to intensive sand mining—a growing environmental concern worldwide.
Cement, concrete, paints and plasters typically rely on minerals rich in calcium and magnesium, which are commonly sourced by extracting sand and aggregates. Today, these materials are mined from mountains, rivers, coastlines and even the seabed—practices that are increasingly unsustainable.
Benefits and potential applications
The material developed by the Northwestern team offers a series of advantages that could make it a game-changer for the construction sector:
- Lower emissions: By capturing more COâ‚‚ than it emits, the process actively contributes to efforts to combat climate change.
- Renewable inputs: It uses seawater and atmospheric CO₂—resources that are practically limitless—ensuring long-term environmental viability.
- Hydrogen co-production: The generation of hydrogen adds further value, opening up additional pathways for clean energy development.
- Versatility: The material can be adapted for a wide range of applications, from structural concrete to architectural finishes and decorative features.
Taken together, these qualities make it a strong candidate for a sector that is rapidly shifting toward more circular and sustainable building practices.
The challenges of large-scale adoption
Despite its potential, the material still faces hurdles before it can be rolled out at scale:
- Industrial scalability: Moving from lab to large-scale production will require investment, pilot testing and process optimisation.
- Cost-effectiveness: Its economic viability compared with conventional alternatives will need to be assessed across various markets.
- Regulatory approval: Like all new building materials, it must meet stringent safety and performance standards before entering the mainstream.
Nonetheless, the team at Northwestern is optimistic. With support from research institutions, investors and policymakers, they believe this new material could be integrated into commercial construction over time.
Turning COâ‚‚ into a resource
Northwestern University’s approach marks a significant step forward in rethinking how we build. By turning CO₂ from a pollutant into a raw material, it points the way towards infrastructure that is not just durable and functional, but also an ally in tackling climate change.
If you are interested in other ways COâ‚‚ is being repurposed as a resource, take a look at our recent article on the subject. And if you would like to stay up to date on the latest breakthroughs in science and technology, you can subscribe to our newsletter at the bottom of the page.
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