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Bacteria used to heal masonry cracks

Self healing 3x2

A bacterial liquid could be used to promote self-healing in stone, slashing maintenance costs for buildings and historic structures.

Engineers at Cardiff University are developing a system to coat buildings in bacteria which produce calcium carbonate, a form of limestone, which would seal any small cracks appearing in masonry. By repairing smaller cracks larger cracks could be prevented from forming, drastically reducing the need for maintenance on stone buildings and historic structures.

Over the next two years the EU-funded trial will graduate from lab-based tests to real world experiments.

Cardiff University school of engineering researcher and the study’s principal investigator Mike Harbottle told New Civil Engineer how the trial developed as an extension of a self-healing concrete study. Harbottle, who has a background in geotechnical engineering, found the bacteria grew more readily in stone than concrete.

“It’s a lot easier to get it to work [in rock] than it is in concrete because concrete is such a harsh environment,” he said, adding the bacteria prefer a ph-neutral, soil-like environment with the right level of nutrients.

“In concrete it’s not a very good environment for life, whereas in masonry, on a rock like limestone or sandstone where there is quite a large pore space…there are living organisms that will naturally colonise these materials anyway.

“It’s a lot more of a benign environment to the organisms so they’ll be a lot happier there and do a better job.”

Harbottle said that one challenge on the trial is keeping the bacteria fed – most live on a diet of sugar. Timescales differ between different types of bacteria too, with some producing sufficient mineral matter in just a few days.

Although it is early in the trial, Harbottle believes a bacterial liquid could cut maintenance time and costs for engineers.

“For example, historic structures where there maybe isn’t the budget to maintain them as much as we’d like, then having something that reduces the level of maintenance may be pretty advantageous,” he said.

A separate £6M self-healing building research project at Cardiff University is trialling other materials such as concrete over the next five years.

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