Materials

New concrete recipe improves its carbon capture efficiency

New concrete recipe improves i...
Samples of the cement paste, containing different concentrations of titanium dioxide and different water-to-cement ratios, were placed into a chamber where they were exposed to higher CO2 concentrations
Samples of the cement paste, containing different concentrations of titanium dioxide and different water-to-cement ratios, were placed into a chamber where they were exposed to higher CO2 concentrations
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A pile of cement powder (left) and the amount of titanium dioxide nanoparticles (right) mixed into the cement to boost its carbon dioxide uptake
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A pile of cement powder (left) and the amount of titanium dioxide nanoparticles (right) mixed into the cement to boost its carbon dioxide uptake
Samples of the cement paste, containing different concentrations of titanium dioxide and different water-to-cement ratios, were placed into a chamber where they were exposed to higher CO2 concentrations
2/3
Samples of the cement paste, containing different concentrations of titanium dioxide and different water-to-cement ratios, were placed into a chamber where they were exposed to higher CO2 concentrations
Scans of the samples before and after exposure to the CO2 chamber reveal that they became more porous
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Scans of the samples before and after exposure to the CO2 chamber reveal that they became more porous
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Concrete is one of the world’s most commonly used materials, and unfortunately its production is a major source of carbon dioxide in the atmosphere. Now, engineers at Purdue University have developed a new cement recipe that can absorb CO2 twice as fast as usual, hopefully turning it into a useful carbon sink.

Concrete production accounts for over eight percent of the world’s carbon dioxide emissions, and with demand increasing every year researchers have been investigating ways to make concrete more environmentally friendly. Some steps have included changing the recipe to reduce or replace the binding agent that produces the chemical reaction that emits CO2. Some alternatives even involve capturing CO2 from other sources and using that in the mix.

But another avenue of research gives the material a more active role. Once it’s laid, concrete naturally absorbs CO2 from the atmosphere over its lifetime. It’s not enough to fully counter the emissions released during its production, but it at least helps reduce the footprint. Some studies have found ways to boost that absorption to make concrete even greener – and now, the Purdue team has discovered a new way to do so.

“We can’t wait decades for concrete to absorb the carbon dioxide produced in its manufacturing process,” says Mirian Velay-Lizancos, lead author of the study. “My team is making the concrete itself absorb carbon dioxide faster and in greater volumes. We’re not trying to change the way we use concrete; we’re making the concrete work for us.”

A pile of cement powder (left) and the amount of titanium dioxide nanoparticles (right) mixed into the cement to boost its carbon dioxide uptake
A pile of cement powder (left) and the amount of titanium dioxide nanoparticles (right) mixed into the cement to boost its carbon dioxide uptake

The secret ingredient is titanium dioxide. By mixing small portions of this material in with the cement paste, the team found that it reduced the size of calcium hydroxide molecules, which made the concrete more efficient at absorbing carbon dioxide.

The team tested the absorption of the concrete by placing samples in a chamber filled with high concentrations of CO2 for 24 hours, then analyzed their mass changes over time and performed 3D X-ray scans of the pore structure. They found that titanium dioxide could almost double the speed at which concrete absorbed CO2.

That said, it wasn’t just a matter of throwing in more titanium dioxide and boosting the effect even further. The team found that it worked up until a certain percentage, before dropping again. That percentage depended upon the water-to-cement ratio and the age of the cement.

The researchers plan to investigate the new cement recipe further, in hopes of making it more sustainable and durable.

The research was published in the journal Construction and Building Materials. The team demonstrates the work in the video below.

New mix could double concrete’s carbon uptake

Source: Purdue University

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4 comments
4 comments
TechGazer
Calling it a 'carbon sink' is misleading. It's not going to recapture 100% of the CO2 released by firing the components, and that doesn't include the CO2 that probably was released in generating the heat needed by the process. Thus, more concrete production = more total CO2 released. A carbon sink is something that reduces the total amount of CO2 in the atmosphere when you produce more of the sink.
Mirian Velay-Lizancos
The production of any construction material has associate CO2 emissions. So, to be clear, more production of any construction material = more total CO2.

Concrete is the most used construction material around the World. This is one of the main reasons why concrete is associate with an important piece of the CO2 emissions cake.

If concrete were not used, another material (that would also have CO2 emissions associated) would be used instead.

Concrete is strong, is cost-effective, fire-resistant, and exhibits great durability, minimizing reconstruction and waste generation.

In fact, it is tough to think of any alternative with the same performance that can bit concrete in terms of sustainability, considering its high durability. In any case, we are also working on that.

Nonetheless, reducing the net CO2 emissions of the most used construction material around the World will have a great impact. And this is what this research is about.
Mirian Velay-Lizancos
Thanks to Michael Irving for this great article on our research! Accurate and very well explained.

Regarding the comment by TechGazer: Any LCA a net CO2 emissions calculations that we perform in our studies DOES include the CO2 released in generating the heat needed by the process to produce cement (one of concrete’s compounds). "Carbon sink" is used in different contexts with different meanings. But, it is clear if you read the post that nobody could understand that we are claiming that the new concrete would possess negative net CO2 emissions, which I think how you define "carbon sink." It is widely accepted that even the regular concrete is a sink of CO2 during its service life. There are papers in top journals about it. But the process is very slow, and the environment can’t wait so much; this is why we are speeding up and enhancing the CO2 sequestration.
Robert Higgins
Good article, but should come with significant caveats. Concrete technology has attempted for decades to REDUCE CO2 uptake, specifically for concrete that is steel reinforced. The high pH (12.45) of calcium hydroxide "passivates" the area around the steel, which prevents corrosion (rust). If this area becomes "carbonated" and the pH surrounding the steel falls below a pH of 11, corrosion becomes a near certainty. This technology should be used ONLY for non-steel reinforced concrete.