Concrete, Heal Thyself

Researchers in the Netherlands are "healing" cracked concrete by including bacterial spores and nutrients at the mixing stage. When activated by water, the bacteria feed on the nutrients and produce limestone, sealing the cracks and greatly extending the service life of the concrete. Given successful trials, self-healing concrete could be commercially available in 2-3 years.

Concrete, like everything else, doesn’t last forever.

Despite being the world’s most widely used building material, an unavoidable side effect of concrete’s hardening process are “micro-cracks,” small fractures that corrode structures when water finds its way in.

"For durability reasons – in order to improve the service life of the construction – it is important to get these micro-cracks healed," Dr Henk Jonkers told BBC News.

Jonkers, along with concrete technologist Eric Schlangen, are “healing” the cracks with limestone-producing bacteria. Bacterial spores and the nutrients they will need are added to the concrete mix in granular form, and remain dormant until water activates them.

The bacteria – from the Bacillus genus, harmless to humans – feed on the nutrients to produce limestone, sealing the cracks.

“In the lab we have been able to show healing of cracks with a width of 0.5mm – two to three times higher than the norms state,” Dr. Jonkers said. Fractures of 0.2mm or less are considered acceptable within industry standards.

The team is currently trying to reduce process costs for the system, but even if the healing agent adds 50 percent to the cost of the concrete, the total cost on a construction project should only increase by 1-2 percent.

The savings in maintenance costs, typically a greater expense than the initial installation, could reduce overall building costs in addition to other advantages.

The research is taking place at Delft Technical University, in the Netherlands, and Jonkers said the next part of the process will include outdoors tests with different types of concrete, large-scale quantities with the healing bacteria included, and two years of monitoring to see how the real-world results last. The team is already talking to several construction firms that may provide help.

“Then, if everybody's happy, we can think about trying to commercialize the product,” Jonkers said.