Concrete is the most used material in the building industry, because it is such a versatile material. But no matter how you tweak it, one thing is certain: at some point it will crack. Stress and weather conditions are the main factors that slowly break the concrete. Of course, it is possible to repair cracks, but this takes time and money, especially when the construction has to be closed down while the reparations take place. Researchers at Technical University Delft (NL) and the company Basilisk Concrete have developed ‘living’, self-healing concrete that can repair itself within three weeks and makes manual repairs superfluous.

Once damaged, cracks in concrete will rapidly become worse if it is not repaired. Water will enter the cracks, and in winter, there are chances that it freezes, causing the cracks to grow. When the cracks appear in hard to reach places, repairing the concrete can become even trickier. When these cracks are deep enough to reach the steel reinforcement, this can corrode, causing serious damage.

The secret of the self-healing concrete is in the bacteria that are mixed in the mortar. These bacteria are enclosed in pellets and can be dormant for 200 years. However, when they come into contact with water and oxygen, they wake up. This can only happen when the concrete is cracked or deconstructed. Fed by nutrients in the pellets, the bacteria will multiply and start to produce calcium carbonate (limestone), filling the cracks. It is not clear if the bacteria can run out of nutrients.

The length of the cracks does not matter, only the breadth. At the moment, the bacteria can fill cracks up to 0.8 mm, though Basilisk claims that this number might increase in the future. The material is repaired within 3 weeks, no matter the length of the crack. It appears that the repaired areas remain visible, like a scar.

Basilisk has also developed a liquid containing the bacteria that can make ordinary concrete self-healing.

Photos: basiliskconcrete.com