If it’s broke, it’ll fix itself

How 200-year-old bacteria might heal the cracks in concrete

Concrete has been used in construction for thousands of years. Think of the Colosseum and the aqueducts of Ancient Rome. In the modern era, builders have sought to make improvements to the mixture’s strength, durability, and eco-friendliness. During the Industrial Revolution, engineers discovered better materials and faster ways to produce concrete. They began strength testing different mixes in 1836. The first concrete road in the U.S. was laid in 1891, and it handles modern auto traffic today. Recently, one company produced a concrete that locks in carbon dioxide as it dries. But through all these changes, one problem has remained unsolved: cracks.

These cracks start out small, but widen over time, which can make structures unstable: when water gets in the cracks, the metal rebar supports will rust and break. Workers can seal the cracks if they are spotted, but by then the damage could already be done, which leads to costly and time-consuming repairs. Even worse damage can occur if the cracks open in places where they won’t be noticed until it’s too late. To solve this problem, a new concrete revolution is under way. Someday, workers won’t have to inspect the dried concrete for cracks, because these cracks will seal themselves. That’s right—seal themselves!

Inspired by the way the human body heals itself after breaking a bone, Professor Henk Jonkers (pictured above) wondered whether it was possible to introduce healing abilities to a man-made material. As a microbiology researcher at Delft University in the Netherlands, Jonkers is particularly fascinated with bacteria. He began to envision embedding concrete with microscopic repairmen.

Knowing that bacteria produce limestone under certain conditions, he theorized that he could help cracks self-heal by adding a couple extra ingredients to the standard mix of sand, cement, and water. The first is a strand of bacteria called Bacillus, whose spores are sealed in biodegradable capsules. The other is the bacteria’s food source, calcium lactate. As a crack forms and water gets in, the water dissolves the capsules and activates the bacteria. The bacteria then consume the calcium lactate and produce limestone, which seals the cracks and protects the structure from further damage.

In the course of developing this concrete, several problems arose. The first was finding the right bacteria to use. Eventually Jonkers selected Bacillus because of its ability to survive in the high alkaline cement mix. Before being mixed into the concrete, the bacteria spores are placed in pods to prevent early activation, where they can survive for up to 200 years. These pods are made of a clay material that is weaker than the original concrete—that’s the second problem. To solve it, Jonkers and his team at Delft are now trying to pinpoint the highest percentage of the healing agent that can be added to the concrete mix before the strength and integrity of the structure is compromised. At the same time, the percentage
cannot be too low, or there might not be any healing agent in any given area where a crack appears.

Self-healing concrete is not in use yet, but scientists are optimistic that it will be soon, as reported in Smithsonian magazine. Right now the pricing is too high for most construction jobs, about double the cost per cubic meter, due to the high cost of calcium lactate. Jonkers hopes to get the cost down as the demand for his concrete increases, and he expects the product to be available in the next few years. Until then, cracks will continue to widen, unnoticed, until someone decides to fix them.

This post was written by Suffolk Construction’s Marketing Intern Morgan Harris. Connect with her on LinkedIn here.

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