A Northwestern University-led team of engineers has discovered an innovative way to store carbon dioxide (CO2) in concrete by using a carbonated water-based solution during the manufacturing process. This new method not only helps sequester CO2 from the atmosphere but also produces concrete with uncompromised strength and durability.

In laboratory experiments, the process achieved a CO2 sequestration efficiency of up to 45%, meaning nearly half of the CO2 injected during concrete manufacturing was captured and stored. This breakthrough could significantly offset CO2 emissions from the cement and concrete industries, which are responsible for 8% of global greenhouse gas emissions.

“The cement and concrete industries significantly contribute to human-caused CO2 emissions,” said Northwestern’s Alessandro Rotta Loria, who led the study. “We are developing approaches that lower CO2 emissions associated with these industries and, eventually, could turn cement and concrete into massive ‘carbon sinks.’ We are not there yet, but we now have a new method to reuse some of the CO2 emitted during concrete manufacturing in this very same material. Our solution is simple technologically, making it relatively easy for the industry to implement.”

Davide Zampini, co-author of the study and vice president of global research and development at CEMEX, added, “This approach to accelerating and accentuating the carbonation of cement-based materials provides an opportunity to engineer new clinker-based products where CO2 becomes a key ingredient.”

Concrete, second only to water as the most consumed material in the world, is essential for infrastructure. To make concrete, workers combine water, fine aggregates (like sand), coarse aggregates (like gravel), and cement, which binds all the ingredients together. Since the 1970s, researchers have explored various ways to store CO2 inside concrete, but previous methods had significant drawbacks.

“Previous methods either involved placing solid concrete blocks into high-pressure CO2 chambers or injecting CO2 gas into the mixture of water, cement, and aggregates during production,” explained Rotta Loria. “However, both methods suffer from low CO2 capture efficiency, high energy consumption, and often weakened concrete.”

In Northwestern’s new approach, researchers leveraged the fresh concrete carbonation process. Instead of injecting CO2 while mixing all the ingredients together, they first injected CO2 gas into water mixed with a small amount of cement powder. This carbonated suspension was then mixed with the rest of the cement and aggregates, resulting in concrete that absorbed CO2 during its manufacturing.

“The cement suspension carbonated in our approach is a much lower viscosity fluid compared to the typical mix of water, cement, and aggregates,” Rotta Loria said. “This allows for quicker mixing and fast chemical reactions that result in calcium carbonate minerals. The result is a concrete product with a significant concentration of calcium carbonate minerals.”

After analyzing their carbonated concrete, Rotta Loria and his colleagues found that its strength rivaled the durability of regular concrete. “A typical limitation of carbonation approaches is that strength is often affected by the chemical reactions,” he said. “But based on our experiments, we show the strength might actually be even higher. We still need to test this further, but at the very least, we can say that it’s uncompromised. Because the strength is unchanged, the applications also don’t change. It could be used in beams, slabs, columns, foundations—everything we currently use concrete for.”

Zampini noted, “The findings of this research underline that although carbonation of cement-based materials is a well-known reaction, there is still room to further optimize CO2 uptake through a better understanding of the mechanisms tied to materials processing.”

This new method presents a promising solution for reducing the carbon footprint of concrete manufacturing while maintaining the material’s essential properties, paving the way for more sustainable construction practices.

By Impact Lab