Micro-capsules and Bacteria to be Used in Self-healing Concrete

A new research project involving the University of Bath, UK, aims to develop novel self-healing concrete that uses an inbuilt immune system to close its own wounds and prevent deterioration.

The life of concrete structures is reduced when the material cracks and water is able to get at the steel reinforcement, causing rust and degradation.

It is therefore for this reason that the team of Bath researchers is aiming to develop a concrete mix that contains bacteria within microcapsules, which will germinate when water enters a crack in the concrete in order to produce limestone (calcite), plugging the crack before water and oxygen have a chance to corrode the steel reinforcement.

Indeed, the self-healing concrete process could vastly increase the lifespan of concrete structures, and would also remove the need for repairs as well as reduce the lifetime cost of a structure by up to 50 percent. In other words, considering the fact that over seven per cent of the world’s CO2 emissions are caused by cement production, using this new technique will have a significant impact on the environment.

But how is this all working? To give more precise details, let’s focus on several researchers’ words:

According to Dr Richard Cooper, from the University’s Department of Biology & Biochemistry, the “cement is highly alkaline, making it a hostile environment for bacteria.” He explains that they “will be assessing different species of bacteria to find one that is able to form abundant spores and which will survive and germinate in this environment. The work will involve finding alkaline-tolerant isolates and testing their biology and physiology”.

Dr Kevin Paine, working for the University’s Department of Architecture & Civil Engineering, adds that “concrete densifies as it hardens, so the pore size decreases to a level where bacteria may be crushed.” This is why the researchers are “looking at enclosing the bacteria in micro-capsules, along with nutrients and calcium lactate which the bacteria will convert when water becomes present and use to fill cracks in the concrete.”

On top of that, Dr Andrew Heath, from the same department, puts forward the point that “self-healing materials are particularly suited to situations where safe access for maintenance is costly, so the outputs of this extended research programme could reduce the life-cycle costs of infrastructure.”

Dr Cooper believes that “including bacteria in concrete offers a double layer of protection in preventing steel corrosion. Not only do the bacteria work to plug cracks in the concrete, the process of doing so uses oxygen present which would otherwise be involved in the corrosion process of the steel bars.”

During the research programme the research team will assess the survival of different species of bacteria in concrete over time. Indeed, these bacteria will be allowed to mature before being ground down to create a suspension, which will afterwards be examined by biologists looking for surviving bacteria.

This project is funded by a £2m EPSRC grant, matched by an additional industrial contribution of just over £1 million. It involves the joint collaboration of researchers from the universities of Bath, Cardiff (the lead partner) and Cambridge.

The University of Bath

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