The University of MichiganNews Services
The University Record Online
search
Updated 11:00 AM May 17, 2005
 

front

accolades

briefs

view events

submit events

UM employment


obituaries
police beat
regents round-up
research reporter
letters


archives

Advertise with Record

contact us
meet the staff
contact us
contact us
 
  Research
U-M professor's work will bend, but not break

A new type of fiber-reinforced bendable concrete will be used for the first time in Michigan this summer, and U-M scientists hope their new material will find widespread use across the country.

The new material looks like regular concrete, but is 500 times more resistant to cracking and 40 percent lighter. Tiny fibers that comprise about 2 percent of the mixture's volume partly account for its performance. The materials added to the concrete are designed for maximum flexibility. Because of its long life, the Engineered Cement Composites (ECC) are expected to cost less in the long run.

"The ECC material has promise for solving some of the deck durability issues we face, such as premature cracking," says Steve Kahl, supervisor, experimental studies group, with the Michigan Department of Transportation's (MDOT) construction and technology division. "We're hoping the ECC will work well, and possibly lower the cost when experience is gained on large scale production."

U-M's ECC technology has been used on projects in Japan, Korea, Switzerland and Australia, but has had relatively slow adoption in the United States, despite traditional concrete's many problems: lack of durability and sustainability; failure under severe loading; and the resulting repair expenses, says engineering professor Victor Li, whose team is developing the composites.

Li, who holds appointments in the departments of civil and environmental engineering and materials science and engineering, says ECC addresses most of those problems. The ductile, or bendable, concrete is made mainly of the same ingredients in regular concrete minus the coarse aggregate. Under excessive strain, the ECC concrete gives because the specially coated network of fibers veining the cement can slide within the material, thus avoiding the inflexibility that causes brittleness and breakage.

Fiber-reinforced concrete is not new, but Li says that U-M's ECC—under development for the past 10 years—is vastly superior to other fiber-reinforced concretes in development today. The key, Li says, is that ECC is engineered, which means that in addition to reinforcing the concrete with microscale fibers that act as ligaments to bond it more tightly, scientists design the ingredients in the concrete itself to make it more flexible. U-M holds four patents with three pending on ECC technologies.

This summer in Ypsilanti, MDOT will use ECC to retrofit a section of the Grove Street bridge deck over I-94. ECC will replace the expansion joint and link the adjacent concrete slabs to form a continuous deck. An expansion joint is a section with interlocking steel teeth that lets the concrete deck move as a result of temperature variations, but major problems occur when joints jam frequently, and scientists expect significant savings by using ECC. Li says state suppliers are being trained to make ECC concrete now.

A patch repair placed on the Curtis Road bridge over M-14 in Ann Arbor in October 2002 has established long-term performance of ECC. The patch, which has experienced three winters of freezing and thawing cycles, has much better crack control than the normal concrete patch placed adjacent to ECC one day earlier, Li says.

While long-term studies still are needed, comparisons by the School of Natural Resources and Environment Center for Sustainable Systems, in conjunction with Li's group, show that during 60 years of service on a bridge deck ECC—compared with regular concrete—is 37 percent less expensive, consumes 40 percent less energy, and produces 39 percent less carbon dioxide, a major cause of global warming.

More Stories