Self Healing Concrete

Concrete will continue to be the most important material used in the construction industry, from the foundation of buildings to the structure of bridges. But most Concrete structures are prone to cracking. Tiny cracks on the surface of concrete make the whole structure vulnerable because water seeps into degrade the concrete and corrode the steel reinforcement, greatly reducing the lifespan of a structure.

Hendrik Jonkers, a microbiologist at Delft University has a plan to increase the lifespan of many civil engineering structures. He has worked closely with civil and structural engineering to learn about the properties of concrete and steel reinforcement, and develop the concrete. His innovation, which embeds self-activating limestone-producing bacteria into building material, is designed to decrease the amount of new concrete produced and lower maintenance and repair costs for different types of structures.

HOW DOES BIOCONCRETE WORK?

Self-healing concrete is a product that will biologically produce limestone to heal cracks that appear on the surface of concrete structures.  Specially selected types of the bacteria genus Bacillus, along with a calcium-based nutrient known as calcium lactate, and nitrogen and phosphorus, are added to the ingredients of the concrete when it is being mixed.  These self-healing agents can lie dormant within the concrete for up to 200 years.

However, when a concrete structure is damaged and water starts to seep through the cracks that appear in the concrete, the spores of the bacteria germinate on contact with the water and nutrients.  Having been activated, the bacteria start to feed on the calcium lactate. As the bacteria feeds, oxygen is consumed and the soluble calcium lactate is converted to insoluble limestone.  The limestone solidifies on the cracked surface, thereby sealing it up. It mimics the process by which bone fractures in the human body are naturally healed by osteoblast cells that mineralize to re-form the bone. The consumption of oxygen during the bacterial conversion of calcium lactate to limestone has an additional advantage.

DEVELOPMENT OF BIO CONCRETE MARK II :

A second self-healing agent that will be much cheaper and also would result in much stronger concrete is being developed in close collaboration with Erik Schlangen. The new healing agent would comprise only 3-5% of the overall volume and the concrete would therefore be much stronger.  The new self-healing agent would be a viable product for most structural concrete applications.  The team still has to do a lot of lab testing which will take another year before the new product is ready for full-scale testing. Jonkers says: “If the cost of the self-healing agent can be brought down sufficiently and the concerns over the long-term effects on the concrete performance properly addressed, then the product could have great potential.”  Virginie Wiktor and Arjan Thijssen in Delft.