Seawater and Carbon Dioxide Can Be Turned into a Solid Building Material

Researchers have shown that seawater and carbon dioxide can be converted into a solid construction material that ends up storing more carbon than is emitted during its production.

This result reframes a basic building input as a potential climate benefit, particularly in places where emissions-heavy industry already sits alongside the shoreline.

Seawater and carbon dioxide become stone

In a small, bench-top reactor, seawater produced pale, sand-like granules that could substitute for aggregate normally dug up for use in concrete.

Alongside collaborators at Northwestern University, Alessandro Rotta Loria demonstrated that this material can be grown directly within a carefully controlled chemical environment.

The resulting solids were not limited to a single format: they could form as loose powders suspended in the liquid or as grains that accumulate on an electrode.

Which form you get hinges on a tight chemical window, raising the broader question of how the material shifts when operating conditions change.

How the reaction works

When an electric current is passed through seawater, the water splits and generates hydroxide ions-charged species that make the surrounding liquid less acidic.

In parallel, carbon dioxide bubbled through the seawater produces bicarbonate ions: dissolved carbon compounds primed to build minerals.

Those components then react with the calcium and magnesium already present in seawater, hardening into calcium carbonate (the same mineral found in limestone and shells) along with a magnesium-rich solid.

The process also releases hydrogen gas, creating a second output that could help support the economics of the approach.

Shaping the mineral mix

Modest adjustments to voltage and current, the carbon dioxide flow rate, and water circulation yielded particles spanning airy flakes through to compact, dense grains.

In certain set-ups the solids adhered to the electrode, whereas in others hydrogen bubbles dislodged them and dispersed them into the solution.

“We showed that when we generate these materials, we can fully control their properties, such as the chemical composition, size, shape, and porosity,” said Rotta Loria.

That controllability is important because concrete, plaster and filler applications all require different combinations of particle size, density and internal void space.

Why sand matters

In a standard concrete formulation, aggregates-sand and gravel that provide bulk-make up roughly 60 to 75 percent of the overall volume.

Swapping out a portion of that mass for reactor-grown material could reduce the need to extract sand from rivers, coastlines and seabeds.

Because the reactor can produce either fine powders or larger grains, the same underlying chemistry could be tuned for multiple building products.

In effect, captured carbon becomes an input manufacturers already consume in vast quantities, offering a more practical outcome than burial alone.

Some mixes become carbon negative

With the most favourable formulations, the resulting material can be carbon-negative, holding on to more carbon dioxide than the process emits.

A mixture split 50–50 between calcium carbonate and a magnesium-rich solid can retain more than half of its own weight as carbon dioxide.

Additional processing via carbonation-a reaction that draws carbon dioxide into solids-allows the magnesium-rich portion to lock away even more.

That extra stage also alters the material itself, shifting the focus from storage alone towards how it performs once built into a structure.

Strength after curing

Over 30-day trials, the deposits continued accumulating around the electrode until they became chunks several centimetres across (inch-scale) rather than remaining as loose powder.

Within these chunks, porosity-the proportion of open space in a solid-still allowed ions to move, enabling growth to continue.

Following further carbonation, compressive strength increased from about 14 kg/cm² (around 200 pounds per square inch) to more than 61 kg/cm² (over 870).

However, very alkaline conditions still caused some aggregate pieces to break apart, indicating that durability will depend on the environments and applications chosen by builders.

Keeping oceans separate

Rather than venting carbon dioxide into open seawater, the researchers envisage the chemistry taking place inside modular reactors positioned near the coast.

In these coastal units, operators could regulate incoming water, capture by-products, and treat the remaining liquid before returning it.

“We could create a circularity where we sequester CO₂ right at the source,” Rotta Loria said.

This matters because a climate solution becomes far harder to justify if it damages the local ecosystems around it.

Future research directions

A 2018 assessment by Chatham House estimated cement production contributes around 8 percent of global carbon dioxide emissions.

For this material to meaningfully reduce cement’s climate impact, the electricity that drives the process would need to be low-carbon and affordable.

At higher voltages, chlorine-related reactions also appeared at the positive electrode, underlining that industrial-scale systems must carefully manage unwanted side chemistry.

More rigorous wear testing is still required, since construction materials are as likely to fail through abrasion and impacts as they are under compressive loads.

Building ingredients that store emissions

Beyond concrete, the same mineral products could supply cement, plaster, paint, or restoration work that requires calcium- and magnesium-rich solids.

Because particles can either grow on an electrode or precipitate freely in solution, manufacturers could tailor outputs to suit different supply chains.

That flexibility may help explain industry interest, as carbon capture is more resilient when it ends in a sellable ingredient.

What is waste gas in one process can become feedstock in another.

Seawater, electricity and captured carbon can now be used to make building ingredients that store emissions, reduce reliance on mined materials and generate useful hydrogen.

Whether this concept becomes routine in construction will depend on reactor engineering, access to clean power, costs, and robust evidence from larger-scale trials.