Northwestern University engineers have come up with a new way to make concrete that uses a carbonated solution to store carbon dioxide (CO2) from the air. It’s easy to make, and the concrete is just as strong and long-lasting as the old ones.

When you think of the different kinds of water—still or sparkling—you probably picture the drinks that a waiter brings out at a restaurant. But these two choices are also useful in the building business.

In the past, cement and water were mixed to make a paste that was used to make concrete. Then, crushed rocks like sand and gravel are added to this paste. When these things are mixed together, they harden and stick to the aggregate to make the solid mass that builders use.

However, this is not a green business. The normal making of Portland cement, which is the most common type, releases a huge amount of CO2. Cement production is the third biggest source of anthropogenic carbon emissions, with 8% of all carbon emissions coming from human activities. The only two bigger sources are fossil fuels and changes in land use.

There are, however, other choices. Because it is naturally alkaline, carbonated concrete has a lot of potential to store CO2. This is because CO2 can be turned into solid crystals mostly made up of calcium carbonate (CaCO3). Because these crystals last longer than structures made of cement, they are a great way to keep CO2 stored.

The idea of using this solution was first put forward in the 1970s, but it didn’t get much attention until recently.

In this way, CO2 can be stored in two different ways: through the through the carbonation of hardened concrete or the carbonation of fresh concrete. In the first method, high-pressure CO2 gas is injected into solid blocks of concrete. In the second method, the gas is added to the mixture of water, cement, and aggregates.

The methods used to do these things, on the other hand, have their limits. It doesn’t matter how often they are used; neither of them is very good at capturing carbon. The process also makes the concrete weaker. up until now.

In tests done in the lab, engineers from Northwestern University were able to capture up to 45 percent of CO2. This means that almost half of the CO2 that was put into the concrete while it was being made was taken in and stored.

“The cement and concrete industries make a big difference in the amount of CO2 that people release into the air,” said Alessandro Rotta Loria of Northwestern, who led the study that came up with the solution.

“We are working on ways to lower the CO2 emissions that those industries produce. Eventually, cement and concrete could become huge “carbon sinks.” We’re not quite there yet, but we now have a new way to reuse some of the CO2 that is released when concrete is made from this same material. And our technological solution is so simple that it should be pretty easy for businesses to use.

How did they do it? The engineers took the fresh concrete method and used it in their method, but instead of adding the gas to the mix at the same time, they added it to the water along with some powder. By mixing this carbonated liquid with the other ingredients, they made concrete that took in CO2 while it was being made.

“Our method of carbonating cement suspension is a much thinner fluid than the mix of water, cement, and aggregates that is usually used in current methods to carbonate new concrete,” Rotta Loria said.

“That means we can mix it very quickly and take advantage of the fact that the chemical reactions that make calcium carbonate minerals happen very quickly.” In contrast to when CO2 is added to fresh concrete mix, the end product has a high concentration of calcium carbonate minerals.

If that wasn’t already a big deal, more testing showed that the new concrete was just as strong and long-lasting as regular concrete.

“One problem with carbonation methods is that the chemical reactions often change the strength,” Rotta Loria said. “However, our tests show that the strength could be even stronger.” Even though we still need to test this more, we can say for sure that it’s safe. The applications don’t change because the strength stays the same. It could be used for everything that concrete is used for now: beams, slabs, columns, foundations, and more.

“The results of this study show that even though carbonation of cement-based materials is a well-known reaction, there is still room to improve the CO2 uptake by learning more about how materials are processed,” Davide Zampini, who helped write the study, said in the end.

The study was written up in Nature.