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Engineers would love it if concrete bridges and skyscrapers didn't require so much maintenance, and they might have found the perfect solution using bacteria.

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You can learn more at [ INTRO ]. Once you start learning about bacteria, you start to realize that they can do basically anything: eat plastic, generate electricity, create the world's strongest glue, and even hold up bridges and skyscrapers.

Yeah, bridges and skyscrapers. Bacteria. It's all thanks to a bizarre connection with concrete.

Concrete is the second most widely used substance on Earth. The only thing we use more of is water… which really makes you realize that we build a lot of stuff. Normally, concrete's mix of cement, water, and aggregates — like sand or gravel — is sturdy.

But it does develop cracks. Then, those cracks can fill with water and ice, which can make them expand even further. If there's a lot of water, it can also rust the steel reinforcements that hold up your structure.

So concrete needs to be maintained. The problem is, that's expensive and a huge hassle — especially if you're repairing something like the Three Gorges Dam in China, or hazardous waste facilities. And since cement production is responsible for around nine percent of the world's CO2 emissions, replacing or reinforcing structures with /more/ concrete is also harmful to the environment.

For years, scientists have been trying to solve this problem by getting concrete to repair itself. And that's where the bacteria come in. A while back, scientists were scouring the bottoms of lakes formed by volcanoes, searching for organisms that survive in extreme conditions.

And they found several species of bacteria that seem like they were made for concrete. First, these intrepid microbes live in alkaline environments, or those with a pH higher than 7. Some of these areas are so alkaline that they can burn your skin — but that's actually great, because good concrete also has a high pH.

The coolest part, though, is that some of these bacteria excrete calcite, a mineral that makes up concrete. And that means they're really useful. A few researchers have been investigating this since 2006, and their teams have come up with a great method for putting these bacteria to work.

First, they place the microbes into biodegradable plastic bubbles or tiny clay pellets, along with some calcium lactate for food. Then, they mix the capsules into concrete. When the concrete is fully intact, these die-hard bacteria remain dormant, trapped in a rocky prison.

But when a crack forms, water seeps in, dissolves the capsule, and wakes up the microbes. The hungry bacteria then eat the calcium lactate and excrete calcite, which bonds to the concrete and fills in the crack. The bacteria are then re-sealed in their prison until another crack forms.

Voilà: self-healing concrete! Assorted studies have shown that bacteria can restore more than ninety percent of concrete's strength through this method. Which is amazing.

The problem right now is that this self-repairing concrete is also expensive — so you probably won't find it at your local hardware store. For now, experts think its smartest use is in places where maintenance is dangerous and massively inconvenient, like in underground chambers storing radioactive waste. But scientists are exploring ways to make it cheaper — like by replacing costly calcium lactate with a sugary food.

One scientist is even developing a bacteria-filled liquid that can be sprayed on regular concrete instead of mixed into it. So someday, these microbes might help support buildings and bridges around the world. Self-healing concrete is a really cool way we could help reduce the world's carbon emissions, but it obviously isn't the only one.

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We've been talking about Brilliant's courses all week, and that's because there's a lot you can learn from them. Sign up at and you can get 20% off an annual Premium subscription. You'll get learn cool things and support our show along the way.

So thank you! [ outro ].