NARRATOR >> each year an average of more than two tons of concrete is poured for every man
woman and child on the planet that makes concrete by far the single most utilized
engineering material on earth.
LEE >> Concrete is a very very good construction
material for many reasons. It is relatively inexpensive it can be formed into
different kinds of shapes relatively easily and its ingredients are widely
available the one shortcoming is the brittleness of this material.
NARRATOR >> In an experiment conducted by University of Michigan Civic and Environmental
engineering professor Victor Lee the steel reinforcement rod embedded in this
structural model was pulled upwards the concrete in which it was anchored
shattered the outcome was much better for Professor Lee's bendable concrete
called engineered cementitious concrete or ECC this is what we call plastic
behavior so the material provides a gift under very extreme loading instead of
fracturing into pieces and still hold a load.
NARRATOR >> ECC's bend but don't break
approach can result in safer buildings.
LEE >> That's how we got started in this work
to enhance structural safety under extreme loading such as during a major
earthquake event or even during man-made disasters like bomb blast for
example we would like to keep the occupants safe
NARRATOR >> another test conducted by research fellow Mo Lee measures bending loads on a
horizontal span.
LEE >> This is the normal concrete specimen under blending mode so
here on the bottom of the specimen will be under tension and the top of the
specimen will be under compression you can see that it has very sudden failure
which correspond well to the catastrophic failure mode of concrete
structures.
NARRATOR >> achieving catastrophic failure on the ECC sample takes four
times as much force and it displays over 300 times the ductability or fendability
of the standard sample and while failure for the standard sample means
snapping in two, the failed ECC stays in one piece. The secret lies in adding
coded microscopic fibers that work together to share the load
LEE >> You can see those
tiny little cracks warmed here those cracks are so little that they are
as tight as human hair according to postdoctoral research
fellow Eric Cycolich there's a side benefit to trading one big crack for
many smaller cracks. Turns out bendable concrete is also self-healing.
SPEAKER >> This is the kind of crack that you would see in regular cement or regular concrete.
It's fairly wide and then down here is a crack that started out much smaller and
it was able to heal much better. All concrete has some capacity for
self-healing but in normal concrete that doesn't work because the cracks are all
very very wide
SPEAKER >> And what kind of exotic chemicals does it take to heal these
micro-cracks?
SPEAKER >> Water and air which fortunately especially here in Michigan
we have we have plenty of both
SPEAKER >> And like any place that has four seasons, Michigan
has plenty of cracks and potholes on roads and bridges. Part of the problem is
that roads are made of a combination of concrete and steel and when steel rusts
it expands a process that can be accelerated with a small electrical current.
SPEAKER >> 120 hours after the current started the concrete cracks and cracked
to a very severe extent so that basically it just fractures the concrete
you can see the corroded steel inside. This is basically what happens often on a
bridge deck where steel is corroded because of the presence of water and
de-icing salts.
SPEAKER >> And while standard concrete failed after 120 hours of the
accelerated corrosion experiment the ECC sample remained intact after three times
as much exposure
SPEAKER >> here's a very small micro crack showing
up and here's another one where the corrosion material comes out so it
experiences damage because of the corrosion of the steel which expands
around it but it accommodates that expansion by being able to plastically
yield.
NARRATOR >> So four states with only two seasons winter and construction just how long
made a road made with ECC last?
SPEAKER >> What we are are hoping to achieve with this newer
material is to extend the service life to as much as 100 years
NARRATOR >> Concrete that
bends, fills itself and makes building safer and roads that can last 100 years
What could possibly be next? How about smart roads that could tell
you how they're doing?
SPEAKER >> We have the ability of self sensing the structure would
always know and report this condition so that repair can be done only when and
where it is needed
NARRATOR >> An infrastructure that's safer more durable and more
sustainable Sounds like a good road forward!