To get ordinary concrete, combine gravel, sand, water, and cement. But substitute a portion of that gravel with highly flexible microfibers and you get self-healing concrete. That’s a simplified explanation of what University of Michigan engineering professor Victor Li (Left) has done, as lead developer of a material called engineered cementitious composite (ECC).
When ECC, or “self-healing concrete,” comes under strain, a calcium carbonate patch forms from the alchemy of two ingredients: rainwater and air. In just one 24-hour cycle, the material can heal itself by up to 80 percent.
Li’s innovation recently received the attention of Popular Mechanics, which included self-healing concrete in its list of “110 Predictions For the Next 110 Years,” declaring that “bridges will repair themselves” within the next decade, thanks to the material.
At the moment, self-healing concrete is several times more expensive than the old-fashioned stuff, Li says, but commercial optimization could bring the cost down. It would make a lot of economic sense in the long run, he says, because material costs are just one factor that determines the total lifecycle cost. “Intelligent” infrastructures that repair themselves are more sustainable, significantly reducing costly repeated maintenance that requires human intervention. Self-healing concrete, Li says, would “reduce, dramatically, the cost of maintenance of our civil infrastructures,” which, as drivers in metro Detroit know, are crumbling.
As for ECC’s healing properties, Li likens it to human skin. “If we get a paper cut, we expect it to re-heal itself … but if we cut not only our skin, but through the whole finger, it’s going to be more difficult for it to repair itself,” he says. The analogy is simple: The greater the damage, the longer the recovery. For ECC, dry environments also foster longer recovery periods, while heavy rainfall leads to more rapid ones — another silver lining for Michigan’s seemingly ceaseless spring showers.
For his newborn son’s generation, Li expects that self-healing concrete will be nothing to be surprised about. “When he grows up in, say, about 15 to 20 years,” Li says, “I would venture to say that our construction materials will not only be self-healing, but in general will be a lot smarter.”
He and his colleagues are already working on other “intelligent” industrial materials, namely “self-sensing” concrete that knows when it needs repair, and “self-adaptive” concrete that adjusts its thermal properties for buildings to use less energy.