Concrete that can repair itself

19 November 2013

Interview with

Abir Al-Tabbaa, University of Cambridge

Chris - When a building gets damaged, you can plaster up the holes or you can knock it down and you can start all over again. But wouldn't it be nice if the building could repair itself? Dr Abir Al-Tabbaa from the University of Cambridge works on self-healing concrete. She's with us now. Hello.

Abir - Hello.

Chris - Is this possible?

Abir - We hope so. This is the work we've just started to do as a big research project - 3 million pounds funded by the government and industry, with our collaborators at Cardiff and Bath Universities. We're trying to develop self-healing construction materials.

Chris - Given that you're spending that much money researching the problem, this means it must be costing industry a lot of money.

Abir - Absolutely, yes. So, a huge amount of money is spent every year on repairing damaged structures.

Chris - So, why does concrete crack because it's effectively rock, isn't it?

Abir - It is rock, but when concrete goes in tension, it cracks. If you have a beam and you apply load to it, some part of it goes in compression. It's stressed against itself and the other one is pulled out.

Chris - So in other words, if you've got concrete being squashed, it's absolutely fine with that, but when you start getting bits of concrete stretched in some way then you're going to get little cracks opening up.

Abir - That's correct.

Chris - So, what sort of price tag is there on this worldwide then and how do you remedy the problem at the moment?

Abir - Repairs cost a huge amount, so we're spending billions of pounds every year repairing damaged buildings and roads and infrastructure generally. It's been left to deteriorate so there's a huge amount of repair to be done.

Chris -   So, how are you trying to make concrete that will fix itself when this happens?

Abir - So, our vision is to encapsulate self-healing elements within the concrete. Actually, we're not just talking about concrete. We're talking about cement materials, so as water and cement as well, and grout.  It's looking at micro capsules, so little bubbles that contain healing agents like glue or resin, and some bacteria that will precipitate sort of natural cements basically and seal the cracks.

Chris - And these things will be put into the concrete when it's being poured for the first time, will they?  So, they're in there.  So, should a crack happen, they can activate.

Abir - That's correct. So, this will revert to a new concrete, but we can also use it for repairing existing structures where you would normally place a cement grout for example so you could place a self-healing cement grout so it doesn't crack again in the future.

Chris - So, why are you putting bacteria in there?

Abir - Well, bacteria will basically produce limestone which is our natural cement and that will fill the cracks and seal them.

Chris - How do the bacteria know to do that then?

Abir - The bacteria will be placed dormant and then the nutrients were also placed separately. When there's a crack and there's water ingress, the water will come in contact with the bacteria and the bacteria will come in contact with the nutrients, and hopefully, start producing limestone.

Matt - So, you're basically trapping these bacteria deep in this concrete. Are they living all this time or how do they survive trapped inside concrete?

Abir - Yeah.  The plan is they remain dormant until they're needed.

Matt - So, they're woken up when their job to repair concrete comes around.

Abir - Exactly.

Matt - So, what are some of the key applications you can see for this self-healing concrete? Obviously, it's one thing to replace the paving stone. That's not a big deal. But I can imagine there are some instances where it's a real pain to have to repair concrete structures.

Abir - Yes, that's correct. So, we're looking for example at roads and infrastructure where you don't really want to have delays or cause disruption. There are also incidents where you are unable to detect or inspect damage. For example, oil wells or nuclear facilities.

Matt - So, these are the kind of facilities. Once you've dug an oil rig in the middle of the ocean, drilling down hundreds or thousands of metres underwater, once they're finished, they have to plug the hole.  Is that plug one of these concrete structures that you're talking about?

Abir - Cement, yes.

Matt - Cement and obviously, you can't be going down to the bottom of the sea to fix that up. Yeah, I can see where a self-healing concrete would be ideal.

Chris - But equally, are the pressures not incredibly high there. So, how do the bacteria cope with being under those immense pressures? Also, if they're under a building, surely, the pressure inside the concrete is enormous too.

Abir - Well, the bacteria, one idea is to encapsulate them and so, in little capsules. So, the shell of a capsule will take all the pressure while the bacteria remains safe inside.

Chris - But then when they crack, breaks open the capsule, they're going to be exposed, aren't they?

Abir - Sure.  I mean, this will be a big challenge. So, part of the challenge is to ensure that the bacteria will survive under those conditions.

Chris - Dare we ask, what the timeframe is?

Abir - Well, we are hoping to do some trials actually within the next 2 years. So, we have a target to produce something feasible in about a year and try that on perhaps the road section.

Matt - Thank you very much, Abir Al-Tabbaa from the University of Cambridge.

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