Self-healing concrete

13 June 2013
Posted by Kate Lamble.

Rusting Steel in Concrete.A £3 million grant has been awarded to teams across Bath, Cardiff and Cambridge universities to investigate a new building technology; self-healing concrete.

Concrete is vitally important for the structural integrity of buildings and foundations and while we might think of it as a long lasting material, over time, tiny little cracks can form which can weaken it.

These cracks let in water, which can freeze and widen the crack through to the steel frame which re-enforces large blocks of concrete. When that steel frame gets corroded, it stops the tension that pulls all the concrete together, weakening it. Repairing this concrete can be costly, but cement production produces around 7% of the world's CO2 production. So, if we can reduce the amount of concrete that we need to repair or replace we can not only save money but also reduce our overall CO2 emissions. 

The idea these teams have come up with is to allow concrete to repair itself by impregnating the liquid concrete with thousands of microcapsules containing bacteria. These bacteria produce calcite, a crystal version of calcium carbonate. So when a crack forms and the microcapsule is broken open, the calcite produced would not only block up the crack to prevent water from getting in but also use up the oxygen in the crack which would stop the metal frame from corroding. 

There are several hurdles to overcome, firstly designing microcapsules which are able to withstand a huge amount of pressure within the concrete but crack open when exposed to water as a crack forms. The bacteria also have to be carefully selected as they have to survive the alkaline conditions of the concrete and survive for potentially hundreds of years. The team are are beginning by selecting bacteria from soda lakes which are used to conditions which a high pH and have decided to use bacteria which produce inert internal spores (similar to although certainly not including anthrax). This way when the capsule is broken open by a crack water can activate the germination of the inert bacteria which will naturally start producing the material to plug up the gap!

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