The issue of stress-induced cracking in concrete can cause large structures like buildings, bridges and highways to lose their stability over time and to become structurally unsound.

A team of scientific researchers at TU Delft, one of the leading universities in the Netherlands, has come up with an innovative solution that uses an unexpected ingredient: natural bacteria.

A natural solution for crack repair

Cracking in concrete is a perpetual headache for engineers, as it requires additional amounts of internal steel reinforcement and/or ongoing repairs. It can also cause the internal reinforcements to rust, which can cause unsightly additional cracking and structural instability.

To find a solution, where the concrete can actually heal itself, the team of researchers, led by microbiologist Dr Hendrick Jonkers, looked in some unlikely places for inspiration, including rock formations close to volcanos.

In such environments the natural bacteria Bacillus pseudofirmus and Sporosarcina pasteurii can be found. These bacteria are not only heat and cold resistant, but can also lie dormant for hundreds of years.

Jonkers found that by mixing the same natural bacteria and their favourite food (calcium lactate) into concrete, they could produce a material with self-healing capacities.

Just add water

This self-healing ability comes into play when water enters concrete through open cracks. The water awakens the bacteria which then consumes its accompanying food. As a by-product they secrete limestone - which just happens to be the main component in concrete.

The newly produced limestone then fills the cracks in the concrete.

This "healing" process takes merely three weeks, regardless of the length of cracks, whether centimetres, metres or kilometres.

In terms of crack width, the scientists have found that this approach is capable of sealing cracks that are up to 0,8cm wide.

Plenty of potential for future uses

In 2015 Jonkers was nominated by the European Patent Office for a European Inventor Award.

The creation of self-healing bio-concrete has the potential to save billions in construction costs by eliminating repair costs as well as reducing the amount of expensive steel required in buildings and other structures.

A spray solution has also been developed to apply to existing buildings.

Sources: Science Alert, TU Delft