Concrete is incredibly sturdy when subjected to heavy compression, but suffers catastrophic cracking under strain–that’s why it snaps so easily in earthquakes. But a scientist in Michigan has just perfected a new concrete mix that changes all that. It’s bendy, and it can heal its own cracks–all it takes is a little rain.
The invention, by professor Victor Li of Michigan University, is a refinement of a research material dubbed “engineering cement composite” or ECC. His lab has been working to perfect this substance for 15 years. Unlike the ceramic behavior of “normal” concrete, the new ECC is a bit more like a metal.
Its amazing properties rely on a chemical and structural mix: In the resulting solid, tiny cracks do still form when the material is bent, but they remain tiny and don’t connect up to each other. The cracks stay around 60 microns in size, allowing the solid to bend, and their propagation is halted by microscopic reinforcing fibers. Furthermore, the cracks are exactly the right size to allow moisture and air in when they form. After a short while to react, “spare” dry cement in the mix reacts with the available carbon dioxide and water to form calcium carbonate–a naturally strong material that then seals up the cracks.
That means the material can suffer bending and stretching loads that would utterly destroy plain concrete and even badly affect steel beams, and still remain firm. As Li puts it, the results were somewhat unexpected: “We found, to our happy surprise, that when we load it again after it heals, it behaves just like new, with practically the same stiffness and strength.”
The implications of a bendable, self-healing concrete are somewhat incredible. Current architectural and civil engineering designs are strictly limited by the material characteristics of plain and steel bar-reinforced concrete. A totally new material could enable radically different building designs that couldn’t be constructed using current materials. The earthquake-readiness of a building made with a bendable concrete structure could also be significantly enhanced. And the self-healing aspects have important ecological implications, giving infrastructure elements like bridges much longer life-spans, negating–or at least delaying–the need for expensive and eco-unfriendly rebuilds.