Turning CO₂ into cement: A new path to greener construction

We often think of carbon dioxide as nothing more than pollution. It’s a byproduct of factories, cars, and power plants – and one of the main drivers of climate change. But what if we could take this waste gas and transform it into something useful?

That’s exactly what scientists at the University of Michigan, along with collaborators from UC Davis and UCLA, have been working on.

The team has developed a method to convert carbon dioxide into metal oxalates, which can be used as building blocks in cement manufacturing.

Putting carbon dioxide to good use

“This research shows how we can take carbon dioxide, which everyone knows is a waste product that is of little-to-zero value, and upcycle it into something that’s valuable,” said Charles McCrory, associate professor of chemistry and macromolecular science and engineering.

“We’re not just taking carbon dioxide and burying it; we’re taking it from different point sources and repurposing it for something useful.”

The work grew out of a project called the Center for Closing the Carbon Cycle (4C), funded by the U.S. Department of Energy. One of the center’s goals is to find practical ways to capture and reuse carbon dioxide, rather than simply releasing it into the air.

Cement with a smaller footprint

The most common type of cement, known as Portland cement, is made by heating limestone and other minerals. This process requires a lot of energy and creates a significant amount of carbon dioxide.

The researchers wanted to flip the script by using CO₂ to create materials that could take the place of traditional cement ingredients.

The team focused on metal oxalates. These are simple salt compounds that can serve as alternative cement precursors.

Scientists have long known that lead could act as a catalyst to help convert carbon dioxide into metal oxalates. The problem? It typically takes a lot of lead to make the process work, and that brings serious environmental and health risks.

A trace amount makes a big difference

That’s where the 4C team made a breakthrough. They used polymers to control the chemical surroundings of the lead catalyst.

This control allowed the experts to cut the amount of lead required down to parts per billion – a level so low it’s comparable to common impurities already found in commercial materials.

“Those metal ions are combining with the oxalate to make a solid, and that solid crashes out of the solution,” explained Mcrory. “That’s the product that we collect and that can be mixed in as part of the cement-making process.”

By adjusting the microenvironment – the chemical makeup around the catalyst – the researchers were able to boost the efficiency of the reaction while using only tiny amounts of lead.

Building cement from CO₂

The process works using a pair of electrodes. One converts carbon dioxide into dissolved oxalate ions. The other, made from metal, releases ions that latch onto the oxalate and form solid metal oxalates. These solids can then be collected and used in cement production.

“Metal oxalates represent an underexplored frontier – serving as alternative cementitious materials, synthesis precursors and even carbon dioxide storage solutions,” said Jesus Velasquez, a co-lead author from UC Davis.

Study co-lead author Anastassia Alexandrova confirmed the science behind the idea using computer modeling.

“Catalysts are often discovered by accident, and successful industrial formulations are often very complicated. These cocktail catalysts are discovered empirically through trial and error,” said Alexandrova.

“In this work, we have an example of a trace lead impurity actually being a catalyst. I believe there are many more such examples in practice catalysis, and also that this is an underexplored opportunity for catalyst discovery.”

Using cement to store CO₂

Once carbon dioxide is locked into metal oxalates, it’s unlikely to return to the atmosphere under normal conditions. That makes the process not just a method of recycling carbon dioxide – but also a way to store it securely.

“It’s a true capture process because you’re making a solid from it,” said Mcrory. “But it’s also a useful capture process because you’re making a useful and valuable material that has downstream applications.”

The team believes their method could eventually be scaled up for industrial use. Much work remains to optimize the production of the final solid product, but the low level of lead required is a key step toward making the process environmentally responsible.

“We are a ways away, but I think it’s a scalable process,” Mcrory added. “Part of the reason we wanted to reduce the lead catalyst to parts per billion is the challenges of scaling up a catalyst with massive amounts of lead. It wouldn’t be environmentally reasonable, otherwise.”

The full study was published in the journal Advanced Materials.

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