Bridges, tunnels and other civil engineering structures could become safer thanks to self-repairing being developed as part of a European research project.
Engineers at Ghent University in Belgium have taken a lead role in the pioneering work. One of the team, Elke Gruyaert, explained the process:
“The concrete is filled with super-absorbent polymers. So when a crack appears, water comes in, and the super-absorbent polymers swell and they block the crack from further intake of water.”
The polymers are added to the concrete mix. Once it is dry, the researchers crack it to see how it reacts. Then they quantify its mechanical behaviour, impermeability and durability.
Brenda Debbaut, an industrial engineer at Ghent University, says the results are very quickly evident:
“If a small crack starts healing immediately, then there is no risk that it grows bigger. So the total structure won’t run the risk of falling down. We want to stop the problem before it is big enough”.
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.
Nele de Belie, Technical Director of the Magnel Laboratory for Concrete Research says impermeability is the key factor:
“You do not have healed concrete regain its strength completely. 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 be used to help concrete repair itself. At Delft University of Technology in the Netherlands, researchers have 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,” says 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 is the difference before healing and after healing,” says Eirini Tziviloglou, another civil engineer at Delft University of Technology
Scientists now aim to implement the technology in real structures.
With around 70% of European tunnels and bridges made of concrete they say these healing agents have significant market potential, as Nele de Belie explains:
“The initial cost will increase. 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”.
More tests are needed but self-healing could become a viable product on the market.