Seawater, electricity and CO2: New carbon-negative materials developed that could replace sand in cement production.
Seawater, electricity and carbon dioxide are all it takes to produce a building material that promises to revolutionise construction. Developed by researchers at Northwestern University, the new material is a carbon-negative aggregate, meaning it captures more CO2 than it emits during production, and is a great replacement for sand, which is currently used to make cement, plaster and paint .
A new filler that is literally made from seawater can capture half its weight in CO2. Scientists have also discovered that they can control its properties in great detail, from its chemical composition to its porosity.
How to Turn CO2 and Seawater into Building Materials
As Earth’s temperature rises, scientists around the world are exploring the possibility of capturing CO2 from the atmosphere and storing it deep underwater or underground to reduce the carbon emissions that are suffocating the planet. However, various carbon capture and storage methods have failed to remove enough CO2 from the air.
So researchers at Northwestern University decided to make the most of the vast amounts of carbon dioxide in the atmosphere by converting it into valuable materials that can be used to make concrete, cement, plaster, and paint.
This new material , described in a study recently published in the journal Advanced Sustainable Systems , is made using seawater , electricity and, of course, carbon dioxide. As Alessandro Rotta Loria , a professor of civil and environmental engineering at Northwestern University’s McCormick School of Engineering who led the study, explains ,
“Cement, concrete, paint and plaster are usually made from or derived from the minerals calcium and magnesium, which are often contained in the aggregate we call sand.”
Currently, these aggregates are extracts from mountains , river beds, beaches and the seabed. But there are other ways to get it without digging and wasting soil. Electricity and CO2 can be used to grow materials like sand in seawater.
A process similar to the growth of coral and mollusc shells.
The new study builds on previous research findings from Rotta Loria’s lab, which focused on storing CO2 in concrete and using electricity to compact sea sand —a promising solution, especially for protecting beaches from erosion. In their latest study, the team used the findings from that project to inject CO2 and apply electricity to seawater in a lab setting. As Rotta Loria explains,
“Our research group is trying to use electricity to innovate in construction and industrial processes. And we like to use seawater because it is an abundant natural resource, unlike fresh water.”
To create the new carbon-negative material, the scientists placed electrodes in seawater and passed a weak electric current through it, which splits the water molecules into hydrogen gas and hydroxide ions. With the electricity on, they pass CO2 gas through the seawater. This process, they say, changes the chemistry of the water, increasing the concentration of bicarbonate ions. The hydroxide ions and bicarbonate ions eventually react with other dissolved ions, such as calcium and magnesium , naturally present in seawater, to form hard minerals , including calcium carbonate and magnesium hydroxide.
Rotta Loria compares the lab process to the technology used by corals and mollusks to form their shells, which uses metabolic energy to convert dissolved ions into calcium carbonate . The researchers simply replaced the metabolic energy needed to run the process with electricity and enhanced the mineralization by introducing CO2.
Concrete of the Future Has No Carbon Emissions (And Doesn’t Harm Marine Life)
During the experiment, the researchers made two important discoveries: not only were they able to create useful aggregates from minerals naturally present in the water, but they were also able to change the composition by manipulating parameters such as the electrical voltage and duration of CO2 injection. The scientists explain that depending on the conditions, the material can be brittle and porous or denser and harder, but it mainly consists of calcium carbonate and magnesium hydroxide. As Rotta Loria explains,
We have shown that when producing this material we can completely control its properties, such as chemical composition, size, shape and porosity. This gives us a certain flexibility and allows us to develop materials suitable for a wide range of applications.
For example, they can be used in concrete instead of sand and gravel, which make up 60-70% of this widely used building material. Or they can be used in the production of cement, plaster and paint . The use of these new materials will not essentially change the basic technical characteristics of cement and concrete.
According to Rotta Loria, industry can implement this production technology using modular reactors in which reactions can take place without disturbing marine life.
“We can create a cycle where we capture CO2 directly from the source. And with a cement plant off the coast, we can use the surrounding waters to power a special reactor where the CO2 is converted with clean electricity into a material that can be used for various purposes in the construction industry. It will then become a true carbon sink,”
