A team of scientists is breathing new life into concrete.
Using a specific strain of bacteria, researchers at Delft University of Technology in the Netherlands have created a type of concrete with the ability to “heal” itself. This technology, once perfected, could make concrete structures more durable, and lead to both big savings in industrial development and greater sustainability.
Concrete is today the most widely used material in the world, present in roads, bridges, and buildings in cities and towns across the globe. From 2002 to 2012, worldwide demand for cement — the key ingredient in concrete — nearly doubled, rising from 1.8 to 3.7 billion metric tons, according to the Inter-American Cement Federation.
For all its usefulness, however, concrete has a major flaw: it cracks. And with cracking comes leakage, which in turn leads to corrosion of the steel reinforcements used to hold up most concrete structures, Prof. Henk Jonkers, who leads the team at Delft, told CNN.
“If they corrode, the structure collapses,” Mr. Jonkers said.
To help solve that problem, Jonkers and his team turned to a kind of bacteria that thrives in high-alkaline substances such as concrete. This bacteria, or “healing agent,” stays intact during mixing and can remain dormant until the concrete cracks and water trickles in.
But that was only part of solution.
“The next challenge was not only to have the bacteria active in concrete, but also to make them produce repair material for the concrete,” Jonkers said.
To do that, he and his team used calcium lactate, a crystalline salt used as an ingredient in baking powder. They then placed the bacteria and the calcium lactate into biodegradable capsules that went into the wet concrete mix.
CNN described the process:
When cracks eventually begin to form in the concrete, water enters and opens the capsules.
The bacteria then germinate, multiply and feed on the lactate, and in doing so they combine the calcium with carbonate ions to form calcite, or limestone, which closes up the cracks.
Due to higher costs, the new substance is not yet a realistic option for residential buildings, according to the project’s page on the Delft University website, but self-healing concrete would be ideal for building underground containers for hazardous waste because “no humans would have to go near it to repair any occurring cracks.” The Delft team is currently looking into improving the distribution of food sources for the bacteria and creating the right environment for it to produce as much crack-closing calcite as possible.
Besides having an impact on public safety and construction, bioconcrete could also benefit the environment by reducing the quantity of concrete used around the world, which would help cut down the material’s massive carbon footprint.
“It is combining nature with construction materials,” Jonkers told CNN. “If we can implement it in materials, we can really benefit from it, so I think it's a really nice example of tying nature and the built environments together in one new concept.”