Self-Healing Concrete 2012

Scientists in the Netherlands have demonstrated a form of self-healing concrete that could revolutionise the construction industry.

Self-Healing Concrete 2012

Credit: TU Delft

The new material is being tested by microbiologist Henk Jonkers and concrete specialist Eric Schlangen, at Delft Technical University. It contains limestone-producing bacteria, which become active when rainwater soaks into the structure. These tiny microorganisms are mixed in with nutrients, lying dormant as spores. If coming into contact with water, they begin to feed on the surrounding nutrients, producing limestone as a by-product.

Concrete is the most common man-made material in the world. 7.5 billion cubic metres are cast each year – more than a cubic metre for every person on Earth. It has a very low coefficient of thermal expansion, however, and shrinks as it matures. Along with corrosive rainwater and chemicals, this gradually results in fractures. As a result, buildings and other structures need substantially reinforcing with steel. However, steel prices are becoming higher, especially with China and India's industrial growth. An alternative is to repair cracks, but this can be very difficult in underground environments, for example.

Self-healing concrete is an ideal solution. It would not only save time and money, but also benefit the environment. The team at Delft Technical University has used bacteria of the bacillus species which have exactly the right characteristics. Their spores can tolerate the highly alkaline environment of the concrete, survive for decades in a kind of sleep mode and without food or oxygen. They will only come to life when cracks appear and water soaks into the concrete. They will then multiply and produce limestone, thereby closing the crack in a few weeks. Once the damage is healed completely, moisture can no longer get into the concrete, so it will not weaken.

Full-scale outdoor testing is now underway. A building in the south of Holland has been covered with the bio-concrete and will be monitored over the next two years. It is hoped that the material can be commercialised by 2015, offering big savings in construction and maintenance costs by extending the concrete's service life.