Bridges, tunnels and roads: Concrete is the main component of our infrastructure. And when the structural elements need to be repaired, it often leads to long traffic jams.
At the Annual Meeting of the AAAS (American Association for the Advancement of Science) in Washington, D.C., Prof. Christian Grosse from the (TUM) and other experts talked about smart materials for sustainable infrastructure.
Small cracks can form in concrete due to permanent loading or variations in temperature. As Prof. Christian Grosse from the Chair of Non-destructive Testing (NDT) at TUM explains, the cracks do not usually pose any direct threat to the stability of structures: “However, water and salts can penetrate the concrete and damage the affected components.”
Repairing infrastructure is expensive and can result in long traffic jams. In the EU research project HealCON, an international team of researchers is working toward the development of concrete that can repair itself. The scientists are examining three different self-healing mechanisms.
– Bacteria as mini construction workers
Certain bacteria produce calcium carbonate as a metabolic product. The scientists soak balls of clay with the spores of these bacteria and mix the balls into concrete. Once water penetrates the concrete, the microorganisms become active and release calcium carbonate, one of the main components of concrete. “The bacteria can close cracks of up to a few millimeters in width in a matter of a few days,” says Grosse.
– Hydrogels as gap fillers
Hydrogels are polymers that absorb moisture. They are used in diapers, among other things. Materials containing hydrogels can expand to ten or even 100 times their original size. Cracks that form in concrete can be healed by a hydrogel that expands when it comes into contact with moisture, thus preventing the water from penetrating further without expanding the cracks.
– Greater strength thanks to epoxy resin
Epoxy resins or polyurethane can be encapsulated and mixed into the concrete. When the concrete cracks, the capsules break open and the polymer is released. It forms a hard mass that seals the crack. It also has a positive side-effect: It increases structural stability.
Looking into concrete
Grosse and his colleagues specialize in testing how well these healing agents work in individual cases. They use non-destructive testing methods to do this, for example acoustic emission technology.