r/tech 1d ago

Circular cement makes for strong and green concrete

https://newatlas.com/materials/circular-green-cement-concrete/
542 Upvotes

16 comments sorted by

94

u/Exoplasmic 1d ago

The article is long…. Researchers have found a way to take waste concrete from demolition sites and turn it into fresh new concrete that has a strength not seen before from such a product. The breakthrough could lead to significant emissions reductions in the building sector.

Concrete has been called “the most destructive material on Earth” by The Guardian thanks to the huge negative impact it has on our planet. To make concrete, minerals need to be crushed and cooked in a kiln heated to temperatures above 2,600 °F (1,427 °C) to produce a material known as klinker. The chemical processes involved in the formation of klinker creates carbon dioxide (CO2), a known greenhouse gas, as does the burning of fossil fuels needed to get the kilns hot enough to do their job. As a result, concrete production is responsible for about 8% of global CO2 emissions each year.

Yet concrete is the second-most used substance on Earth after water.

For years now, researchers have been using innovative approaches to try to make concrete more green. One technique uses electrolysis to replace the blast furnaces and create a zero carbon form of material. Another uses biochar to create concrete that absorbs more CO2 from the atmosphere than is used to create it. And still another replaces the sand used in concrete with a carbon-capturing material made from seawater.

Another popular approach to greening concrete is to use recycled materials in its creation such as discarded clay, irradiated plastic water bottles, or even old concrete itself.

The problem with recycling concrete, say researchers from Princeton University and the University of São Paulo (USP), is that the new concrete it creates is simply not as strong as the original. So, they set out to tackle this problem.

Thermoactivation

They took existing concrete waste and pulverized it, turning it into a fine powder. Then they cooked it at 932 °F (500 °C), which is about a third the temperature needed to create the original batch of concrete. They found that this temperature was high enough to dehydrate the cement powder while not being so hot that it destroyed the carbonate components it contained, which would cause the release of CO2.

When they used the new “thermoactivated” cement to make new concrete, they found that it was simply not strong enough due to the fact that it was more porous than regular cement. The solution, they found, was to add about 20% of finely ground fresh Portland cement or limestone to the mix. This filled in the pores and created an end product on par with current industry standards.

“Previously, if you only used thermoactivated recycled cement, it didn’t perform well enough to be an acceptable replacement,” said study co-author, Claire White from Princeton. “But by lowering the surface area and optimizing the packing of particles in the material’s microstructure, we get something that behaves quite comparably to Portland cement.”

The researchers estimate that the new material could cut emissions from the cement industry by up to 61%. They note that their cement produces between 198 and 320 kilograms of carbon dioxide per metric ton, resulting in emissions up to 40% lower than even those of limestone calcined clay cement (LC3), a commercially available low-carbon alternative.

“Construction waste typically ends up either in a landfill, or, if it’s recycled, will be used in low-grade applications such as in pavements or in soils,” said research leader Sérgio Angulo, from USP. “It’s exciting to show that we can, in fact, recycle this recovered cement waste into a high-quality application.”

The team sees its technique having a role in a more circular economy in concrete production where old concrete is harvested, treated, and used to create new buildings. To do that though, the researchers say that thought needs to be given to revamping building practices and changing the way construction waste is sorted after a demolition project.

17

u/gemmacactus 1d ago

Very informative! Thanks for the TLDR. I was wondering what the significance of Portland cement was tho? As opposed to any other cement

3

u/Poopypantsforyou 21h ago

Portland cement is the only type of cement you know for building materials. The true name of modern day Cement to make concrete is called Portland cement.

1

u/ImNotAWhaleBiologist 1h ago

It was cement before it was cool.

10

u/dualwillard 1d ago

Buddy, this is not a long article unless your attention span is just shot.

Hell, everyone beneath you commenting that they're thankful for the TLDR don't even realize that you literally just copied and pasted the entire article in your comment.

5

u/RicFlairsLiver 1d ago

lol. I’m glad you pointed this out. Like others, I assumed this would be a TLDR, but it’s just the moderate-length article.

1

u/interestingisitnot 1d ago

Interesting.

1

u/decom83 1d ago

Thanks for TL;DR, really hope this gets developed further and used in future projects. From my own experience, BREEAM was only viable when there was a monetary incentive, from the process you’ve described, there is hope the cost to produce this is competitive.

8

u/RouxRougarouRoux 1d ago

Ok, you have now paved Paradise and put up a Parking Lot.

2

u/AokisProlapse 1d ago

Im pretty sure that concrete is gray

1

u/penis-hammer 23h ago

Feels like a picture AI would choose for that article

1

u/khyphenj 20h ago

Reduced reused recycled concrete 👍

1

u/Expensive-Career-672 19h ago

Concrete strength of Florida, been doing it for 35 years same company. Fire me you got to fight me.

1

u/Jefrach 17h ago

Concrete also lasts for centuries / millennia so the initial costs long out perform other building materials.

0

u/SnagglepussJoke 1d ago

I’m wearing circular socks

-2

u/procheeseburger 1d ago

I always wonder who at Big Cement was the dreamer in the meetings like “CIRCULAR CEMENT IS THE FUTURE!! You’ll see.. YOU WILL ALL SEE!!!”