Engineers at the University of Cincinnati's civil engineering department are ecstatic about what they say are vast improvements in the quality of the cement they're now mixing. They are working on a new recipe for bridge concrete they
believe could last for up to 80 years without needing maintenance, will make bridges twice as strong, and lower the cost of bridges by reducing the amount of steel used in its construction.
The engineers are working on what is known as high-performance concrete (HPC). A prototype bridge using the new concrete will be built this fall in east central Ohio and is one of eight around the country being built under a special Federal Highway Administration program to introduce improved technology to bridge-building. The new concrete will allow the erection of longer concrete beams, which can handle more stress and endure greater torture from the elements.
Normally even to cross a small creek, a concrete bridge must use piers and
separate spans. With HPC, a single span can be built across the same area, meaning less expensive construction. "With the material and the design we're using for this particular bridge, we're able to eliminate the pieces which would have been sitting in the water, collecting debris," said Michael Basehart,
associate professor of civil engineering at the university.
Tests have demonstrated that the Cincinnati concrete mix is stronger than conventional concrete, about three times as strong as sidewalk concrete and twice as strong as normal bridge concrete, according to Richard Miller, associate professor of engineering at the University of Cincinnati.
The university engineers also conducted a wide range of durability tests on the concrete used in a sample beam.
Based on the tests, Miller says the concrete beams could last for up to 80 years without major maintenance because the denser material prevents road salt
from permeating the reinforcing steel inside. The material also is more resistant to freeze-thaw cycles, a common road-killer in temperate climate zones.
"In Cincinnati, for example, you might get 20 cycles of freeze-thaw each year. The concrete we've developed has been through 300 simulated freeze-thaw cycles without any problems," said Miller.
In addition to the cost benefits of the single span design and reduced maintenance costs, there also is a benefit to the local community where bridges are built. "A lot of steel needs to be imported, but all concrete is made locally. You can't import concrete, so it's a local job producer," explained Miller.
The Portland Cement Association named nine winners in its Fifth Biennial Bridge Awards Competition. The awards program was instituted in 1988 to recognize excellence in design and construction of concrete bridges.
The winners were selected by a jury of three prominent bridge engineers; Frederick Gottemoeller, president Frederick Gottemoeller & Associates Inc., Columbia, Md.; James R. Hoblitzell, structural engineer, Federal Highway Administration, Washington, D.C.; and James E. Roberts, director, engineering services and chief structures engineer, California DOT, Sacramento.
And the winners are:
The Big Qualicum Bridge, a 856-ft-long bridge carrying the new four-lane Vancouver Island highway almost 100 ft above the Big Qualicum River and Hunts Creek on the east coast of Vancouver Island, British Columbia.
The Depot Road Bridge is a pre-cast arch culvert in Covnetry, Conn., which replaced a deteriorating stone arch built in the early 1800s.
The Kellogg CBD Viaduct in Wichita, Kan., carries U.S. 54 across the Arkansas River and through the central business district. Aesthetic concerns strongly influenced the design.
The Log Farm Access Bridge is a 243-ft-long, rigid-frame bridge spanning
Highway 416 as it enters Ottawa, Ontario.
The North Santiam River Bridge in Gates, Ore., is a two-lane highway bridge that combines prestressed concrete bulb-tee girders with cast-in-place concrete pier tables to extend the span of the 60-in.-deep girders.
The 1,414-ft-long Los Angeles River Bridge carries the Pasadena Blue Line light-rail system across the Los Angeles River in Los Angeles.
The Rockcut Bridge features 7.5-ft-deep bulb-tee girders with an integral deck to increase the speed and ease of construction by eliminating deck formwork and the placement of cast-in-place concrete.
The final two winners involved reconstruction and rehabilitation of Bridges. The reconstruction of the historic Mendota Bridge crossing the Minnesota River Valley near Mendota, Minn., involved among other things, widening the bridge from 60 to 92 ft. The Portage Avenue Culvert at Omand's Creek in Winnipeg, Manitoba, involved the rehabilitation of a deteriorating
single-span reinforced concrete arch culvert.