Reporter Volume 25, No.9 October 28, 1993

By ELLEN GOLDBAUM
News Bureau Staff
If structural engineers could tell precisely where tiny cracks in
concrete begin, they might be able to repair them before they grow
into dangerous fractures.
With "smart concrete," a new, electrically conductive material
developed recently at UB, they may now be able to do just that.  
The new material is also stronger than ordinary concrete, and acts to
shield electromagnetic radiation. Unlike other materials developed for
"smart structures," the new concrete does not rely on sensors embedded
into the material to track structural flaws. Instead, tiny carbon
fibers mixed into the concrete with a conventional concrete mixer make
the material intrinsically "smart." 
The material is described in a paper to be published in a forthcoming
issue of Smart Materials and Structures. 
"The carbon fibers are distributed everywhere throughout the concrete
on a microscopic scale so its conductivity is 10 times higher than
that of ordinary concrete," explained Deborah D.L. Chung, UB Niagara
Mohawk chair of materials research, professor of mechanical and
aerospace engineering and author of the paper with doctoral candidate
Pu-Woei Chen.
"The concrete's electrical resistance will increase in the presence of
a flaw," she said.
The change in resistance is easily detected by electrical probes
placed on the outside of structures. Such probes could either be
permanently attached to structures in strategic locations, providing
continuous monitoring, or they could be applied whenever engineers
suspect there is a flaw. 
"Because the fibers protrude out of the concrete a little, the contact
resistance between the metal probe and the concrete is small, making
probing convenient," Chung said.
In addition to revealing its structural health, the smart concrete
turns out to be tougher than ordinary concrete and stronger flexurally
because of the presence of carbon fibers. It's also capable of
shielding electromagnetic radiation, making it potentially useful as a
building material for electric power plants, military structures and
nuclear reactors. 
According to Chung, the carbon fibers reduce by 90 percent the amount
that concrete will shrink during drying. "When you put all these
attractions together, the extra expense of about 20 percent is
manageable," she said.