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Bridges, tunnels and other engineering structures could become safer thanks to self-repairing concrete developed as part of a European research project.

“The concrete is filled with super-absorbent polymers,” said Elke Gruyaert, an engineer at Ghent University in Belgium, which took a lead role in the research. “So, when a crack appears, water comes in, and the super-absorbent polymers swell and they block the crack from further intake of water.”

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The polymers add into the concrete mix. Once it is dry, the researchers crack it to see how it reacts. Then they quantify its mechanical behavior, impermeability and durability.

“If a small crack starts healing immediately, then there is no risk that it grows bigger,” said Brenda Debbaut, an industrial engineer at Ghent University. “The total structure won’t run the risk of falling down. We want to stop the problem before it is big enough.”

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Scientists working on the European-backed research project think these elastic polymers can indeed protect structures bearing dynamic and mechanical loads. In bridges and tunnels even tiny cracks turn into potentially dangerous damage.

“You do not have healed concrete regain its strength completely,” said Nele de Belie, technical director of the Magnel Laboratory for Concrete Research. “It’s strong enough as it is. What you do want to regain is the liquid tightness and impermeability, so that durability still remains fine.”

There are other biological products that can end up used to help concrete repair itself. At Delft University of Technology in the Netherlands, researchers identified another agent to help concrete self-heal: Bacteria.

“These are bacteria that we have isolated from locations in our planet that have conditions which are similar to concrete,” said Henk Jonkers, a biologist at Delft University of Technology. “One condition is rock-like. The other condition is being very alkaline, so very high PH conditions. These bacteria like to grow under those conditions. These bacteria are not pathogenic, and are not harmful for human beings or for the environment.”

As soon as a small crack appears, bacteria contained within the concrete mixes with leaked water, creating calcium carbonate that seals the crack. Researchers are currently testing how impermeable the bacteria-driven sealing really is.

“We are trying to see if the liquid can penetrate through our healed crack, by how much, and what is the difference before healing and after healing,” said Eirini Tziviloglou, another civil engineer at Delft University of Technology.

With around 70 percent of European tunnels and bridges made of concrete they say these healing agents have significant market potential.

“The initial cost will increase,” de Belie said. “But then if you can reduce the maintenance costs and you increase the service life of the structures, then at the end, this self-healing concrete presents an economically positive picture.”

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