Bubbly water helps CO2 get stored in concrete

Carbonated water may be the key to storing CO₂ properly in concrete, according to a new study published in Communications Materials.

“The cement and concrete industries significantly contribute to human-caused CO₂ emissions,” says senior author Alessandro Rotta Loria, a professor at Northwestern University, US.

“We are trying to develop approaches that lower CO₂ emissions associated with those 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 as a result of concrete manufacturing in this very same material. And our solution is so simple technologically that it should be relatively easy for industry to implement.”

Rotta Loria, along with colleagues from Northwestern and international building materials company CEMEX, found their method was 45% efficient at storing CO₂, while still preserving the strength of the concrete.

There are plenty of projects around the globe aimed at storing CO₂ in concrete. Generally, these projects involve adding CO₂ to wet mixes or dry blocks, so that some of the minerals inside the concrete react to become stronger compounds like calcium carbonate (CaCO₃).

But many of these processes are low in efficiency, taking up very little CO₂, or produce weaker concrete.

This new approach added the CO₂ at an earlier step: the researchers injected the gas into water, along with a small amount of cement powder.

“The cement suspension carbonated in our approach is a much lower viscosity fluid compared to the mix of water, cement and aggregates that is customarily employed in present approaches to carbonate fresh concrete,” says Rotta Loria.

“So, we can mix it very quickly and leverage a very fast kinetics of the chemical reactions that result in calcium carbonate minerals.

“The result is a concrete product with a significant concentration of calcium carbonate minerals compared to when CO₂ is injected into the fresh concrete mix.”

The researchers strength-tested their new concrete and found it comparable to commercial concrete.

“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,” says Rotta Loria.

“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.”