Self-healing concrete for safer, durable, and cheaper-to-maintain infrastructure

The term “self healing” leads one to think about eastern religions, but researchers at the University of Michigan applied it to concrete: the concrete material they developed can heal itself when it cracks. No human intervention is necessary — just water and carbon dioxide.

As the Obama administration contemplates how to direct billions of dollars to rehabilitate the aging U.S. infrastructure — just one example: experts estimate that there more than 70,000 bridges in the the United States which are structurally deficient — it is good to know that handful of drizzly days would be enough to mend a damaged bridge made of the new substance. Self-healing is possible because the material is designed to bend and crack in narrow hairlines rather than break and split in wide gaps, as traditional concrete behaves.

“It’s like if you get a small cut on your hand, your body can heal itself. But if you have a large wound, your body needs help. You might need stitches. We’ve created a material with such tiny crack widths that it takes care of the healing by itself. Even if you overload it, the cracks stay small,” said Victor Li, the E. Benjamin Wylie Collegiate Professor of Civil Engineering and a professor of Materials Science and Engineering. A paper about the material, titled “Autogenous healing of engineered cementitous composites under wet-dry cycles,” is published online in Cement and Concrete Research. It will be printed in a forthcoming edition of the journal.

In Li’s lab, self-healed specimens recovered most if not all of their original strength after researchers subjected them to a 3 percent tensile strain. This means they stretched the specimens to 3 percent beyond their initial size. It is the equivalent of stretching a 100-foot piece an extra three feet-enough strain to severely deform metal or catastrophically fracture traditional concrete. “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,” Li said. “Self-healing of crack damage recovers any stiffness lost when the material was damaged and returns it to its pristine state. The material can be damaged and still remain safe to load.”

The engineers found that cracks must be kept below 150 micrometers, and preferably below 50, for full healing. To accomplish this, Li and his team improved the bendable engineered cement composite, or ECC, they have been developing for the past fifteen years. More