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Andrew Careaga
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NEW MATERIALS HOLD PROMISE FOR FIXING AILING INFRASTRUCTURE
ROLLA, Mo. -- It isn't your typical Band-Aid approach to the problems of decaying roads, bridges and buildings. But new lightweight materials that can be wrapped like a bandage around deteriorating concrete beams and columns hold promise as a cost-effective solution to infrastructure problems, according to a University of Missouri-Rolla professor.
Dr. Antonio Nanni, the Vernon and Maralee Jones Professor of civil engineering at UMR, says new composite materials -- such as sheets of carbon fiber- reinforced polymers (FRPs) that can be "wallpapered" over a damaged portion of a structure -- could help solve the nation's infrastructure problems. They are lighter than steel reinforcement bars, yet stronger, and they may be cost-effective over the long run, Nanni says.
"In the repair and rehabilitation of building and civil infrastructure, these FRP materials may be very competitive on a first-cost basis," says Nanni, an expert in concrete and new materials. "Composites are also much more durable than steel, as well as lightweight and, we hope, corrosion-free. However, we have not yet fully determined the durability of these materials for construction-type applications."
Such composite materials have been used in the aerospace industry, but are new to the construction business. Concerns about ailing infrastructure, however, are leading Nanni and others to look at them as a possible solution to road, bridge and building problems.
Recent reports about the nation's civil infrastructure have raised concerns nationally. According to a 1997 report from the Federal Highway Administration, one of every four bridges on the National Highway System, the backbone of America's road network, is obsolete or has structural problems. In Missouri, about 44 percent of bridges are considered deficient.
Carbon and other fibers -- including corrosion-free glasses and a fiber known as aramid -- hold promise for repairing not only roads and bridges, but also buildings and other structures, Nanni says. He is working with several organizations to test the effectiveness of these new repair and strengthening methods.
Nanni and his research team recently traveled to southern California to test the ability of these carbon composites to strengthen a 35-year-old, pre-stressed concrete deck that was weakened due to corrosion of its steel tendons. To strengthen the deck, sheets of carbon fiber were externally bonded to the top and bottom surfaces. Testing showed that the carbon fiber sheets improved the deck's ability to withstand the design loads.
This rehabilitation method, known as "externally bonded reinforcement," is "ideal when you are rehabilitating existing structures," Nanni says. "You are not increasing the structural member's thickness or adding any weight to the structure."
Carbon fibers are anywhere from two to eight times stronger than steel, depending on the grade of steel, Nanni says.
While Nanni emphasizes the usefulness of these new materials in rehabilitating existing infrastructure, he also is involved in research on using these materials for new construction. Through a grant from the Federal Highway Administration, Nanni will test pre-stressed concrete girders and piles that use fiber- reinforced polymers rather than steel tendons for pre-stressing. Working through a subcontract with the University of Wyoming, Nanni and his team will test 40-foot- long girders in UMR's Engineering Research Laboratory.
Nanni also recently received a grant from the National Science Foundation to study the use of externally bonded FRP composites to repair reinforced concrete structures.
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