Self-Healing Concrete

This is look at Victor Li’s latest innovation: self-healing concrete. Cement and Concrete Research
is soon to publish a paper by Li, who is a professor in materials
science and engineering at the University of Michigan, that describes a
form of concrete that forms many tiny cracks when overloaded instead of
a few large ones, leading to a process in which the concrete
effectively “heals” itself.

Even after a 3 percent tensile strain, Li’s samples recovered nearly
all of its original strength. “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.”

Li and his research group have spent more than a
decade developing what he calls engineered cement composites. An early
version of this ECC is what made the bendable concrete possible. The
current version of ECC keeps cracks under 60 micrometers. The cracks,
though small, expose small amounts of unhydrated cement in the
concrete. When the concrete is subjected to water and carbon dioxide,
it forms a tiny calcium carbonate “scar.” Li found in his lab that
between one and five wet-dry cycles are needed to reach final level of
healing.

This kind of thing is always great stuff, but
cost-benefit analyses often deflate some great innovation. Here, the
question is whether a signficant extension in the lifespan of something
like a concrete highway can offset the premium paid for ECC-enhanced
materials that at one point were looking like they would cost
three-times as much as traditional concrete. Nevertheless, U-M says it
is is pursuing patent protection for the intellectual property, and is
seeking commercialization partners to help bring the technology to
market.

Li delivered a keynote address
on self-healing concrete at the International Conference on
Self-Healing Materials in Chicago in June 2009.

Also see the video about Li’s bendable concrete.