Simple New Process Stores CO2 in Concrete without Compromising Strength (2024)

Research

Carbonated concrete offers potential to offset emissions from cement manufacturing

Jun 26, 2024Amanda Morris

The Problem

High CO2 emissions from the cement and concrete industries can be dangerous to the environment.

Our Idea

A method to sequester CO2 in concrete without compromising its strength and durability.

Why It Matters

The method offers a way to significantly reduce CO2 emissions from the cement and concrete industries, helping combat climate change.

Our Team

Professor Alessandro Rotta Loria

By using a carbonated — rather than a still — water-based solution during the concrete manufacturing process, a Northwestern University-led team of engineers has discovered a new way to store carbon dioxide (CO2) in the ubiquitous construction material.

Not only could the new process help sequester CO2from the ever-warming atmosphere, it also results in concrete with uncompromised strength and durability.

In laboratory experiments, the process achieved a CO2sequestration efficiency of up to 45 percent, meaning that nearly half of the CO2injected during concrete manufacturing was captured and stored. The researchers hope their new process could help offset CO2emissions from the cement and concrete industries, which areresponsible for 8 percent of global greenhouse gas emissions.

Thestudy was published June 26 in Communications Materials, a journal published by Nature Portfolio.

“The cement and concrete industries significantly contribute to human-caused CO2emissions,” said Northwestern’sAlessandro Rotta Loria, who led the study. “We are trying to develop approaches that lower CO2emissions 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 CO2emitted 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.”

Simple New Process Stores CO2 in Concrete without Compromising Strength (1)

Our solution is so simple technologically that it should be relatively easy for industry to implement.

Alessandro Rotta LoriaLouis Berger Assistant Professor of Civil and Environmental Engineering

“More interestingly, this approach to accelerate and accentuate the carbonation of cement-based materials provides an opportunity to engineer new clinker-based products where CO2becomes a key ingredient,” said study coauthor Davide Zampini, vice president of global research and development at CEMEX.

Rotta Loria is the Louis Berger Assistant Professor of Civil and Environmental Engineering at theMcCormick School of Engineering. The study was a collaboration betweenRotta Loria’s laboratoryand CEMEX, a global building materials company dedicated to sustainable construction.

Limitations of previous processes

A non-negotiable part of infrastructure, concrete is one of the world’s most consumed materials — second only to water. To make concrete in its simplest form, workers combine water, fine aggregates (like sand), coarse aggregates (like gravel), and cement, which binds all the ingredients together. Since the 1970s, previous researchers have explored various ways to store CO2inside concrete.

“The idea is that cement already reacts with CO2,” Rotta Loria explained. “That’s why concrete structures naturally absorb CO2. But, of course, the absorbed CO2is a small fraction of the CO2emitted from producing the cement needed to create concrete.”

Processes to store CO2fall into one of two categories: hardened concrete carbonation or fresh concrete carbonation. In the hardened approach, solid concrete blocks are placed into chambers where CO2gas is injected at high pressures. In the fresh version, workers inject CO2gas into the mixture of water, cement and aggregates while concrete is being produced.

In both approaches, some of the injected CO2reacts with the cement to become solid calcium carbonate crystals. Both techniques, however, share deal-breaking limitations. They are hindered by low CO2capture efficiency and high energy consumption. Even worse: The resulting concrete is often weakened, hampering its applicability.

45%

The process's CO2sequestration efficiency, storing and capturing nearly half of the CO2injected during concrete manufacturing

Uncompromised strength

In Northwestern’s new approach, the researchers leveraged the fresh concrete carbonation process. But, instead of injecting CO2while mixing all the ingredients together, they first injected CO2gas into water mixed with a small amount of cement powder. After mixing this carbonated suspension with the rest of the cement and aggregates, they achieved a concrete that actually absorbed CO2during its manufacturing.

“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,” Rotta Loria said. “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 CO2is injected into the fresh concrete mix.”

Simple New Process Stores CO2 in Concrete without Compromising Strength (2)

After analyzing their carbonated concrete, Rotta Loria and his colleagues found 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.”

“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 the CO2uptake through better understanding of the mechanisms tied to materials processing,” Zampini said.

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Simple New Process Stores CO2 in Concrete without Compromising Strength

Carbonated concrete developed by Professor Alessandro Rotta Loria offers the potential to offset emissions from cement manufacturing.

Simple New Process Stores CO2 in Concrete without Compromising Strength (2024)

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