Big news for concrete fans: scientists have figured out how to extend the lifespan of the pervasive building material by up to four times – and the secret was in our blood all along.
In a paper published last week in Applied Materials Today, researchers from Worcester Polytechnic Institute explained how they took inspiration from the human body to develop their new concrete. The result, they say, is a building material that can “heal” cracks in the same way our bodies can heal a cut or scratch.
“It sounds sci-fi,” said lead author Nima Rahbar, “but it’s a real solution to a significant problem in the construction industry.”
Now, there’s a reasonable chance that when you see the word “concrete”, your reaction is less “ooh, interesting, please continue!” and more “oh, yeah, concrete, that gray stuff that made a bunch of weird architecture possible”. But that’s not fair, because concrete is interesting: it’s the most widely used substance on the planet, and by some estimates now outweighs the combined mass of every tree, bush, and shrub in the world.
As the global use of concrete continues to grow, so too does the industry’s devastating environmental impact. Concrete production is now responsible for nearly a tenth of global greenhouse gases – to put it another way, if concrete were a country, it would be second only to China and the USA in CO2 emissions.
One of the biggest reasons for this massive environmental cost is that concrete just doesn’t last that long. Until we figure out what made the Parthenon so durable, our modern cement structures will continue to crack and deteriorate after as little as a decade. More cracks mean more cement is needed to fill those cracks, and therefore more damage to the environment.
“The global use of concrete is ubiquitous,” explained Rahbar. “If tiny cracks could automatically be repaired when they first start, they won’t turn into bigger problems that need repair or replacement.”
This new development is certainly a huge step in the right direction. It isn’t the first type of self-healing concrete we’ve seen, but the team believes it has many advantages over other, mostly bacteria-based, methods. It is “significantly faster”, notes the paper, capable of closing millimeter-scale cracks in just 24 hours – current methods, it explains, need a minimum of four weeks to do the same. It’s also cheap, safe, and odorless compared to bacterial concrete, and it avoids the uncertainties of potential health risks from other types of concrete. And it’s versatile: the team have developed not just the new concrete itself, but also a cement mix that can be applied to cracks in traditional concrete.
“Healing traditional concrete that’s already in use is critically beneficial,” explained Rahbar. “[This] will help reduce the need to produce and ship additional concrete, which has a huge environmental impact.”
Perhaps most tantalizingly, it actively consumes CO2 – a fact which stands in contrast to traditional concrete production. And as with so many innovative scientific solutions, nature got there first: the concrete works by using carbonic anhydrase, an enzyme found in red blood cells that helps carbon dioxide transfer and conversion. When a crack forms in the concrete, this enzyme reacts with carbon dioxide in the atmosphere and starts to produce calcium carbonate crystals. The crack is automatically filled in with these crystals, which are similar to concrete in structure and strength.
“We looked to nature to find what triggers the fastest CO2 transfer, and that’s the CA enzyme,” Rahbar said. “Since enzymes in our bodies react amazingly quickly, they can be used as an efficient mechanism to repair and strengthen concrete structures.”