A unique structural wrapping technique, developed over the last 20 years, is providing a new affordable option to replacement of West Virginia’s many structurally deficient bridges.
Essentially a thick mortar cover bound tightly by a carbon fabric and resin, the technique has been used to rehabilitate nearly 30 bridges statewide, keeping them safe and operable. And, researchers say, it has done so at a fraction of the cost of replacement.
|West Virginia has more than 6,700 bridges and ranks among the top 25 percent of states with significant bridge deficiencies. The state’s New River Gorge Bridge, 876 feet high, opened in 1977.|
The technique has been developed at West Virginia University’s Constructed Facilities Center, founded in 1988 and still directed by Dr. Hota GangaRoa, a professor of civil and environmental professor and a leading researcher in the study of structural deterioration and rehabilitation.
CFC serves a number of federal and state agencies, conducting interdisciplinary research in composite materials, diagnostic tools, design procedures and structural components.
The wrapping technique has proved so successful that CFC and the state Division of Highways have embarked on a partnership that may use it to rehabilitate 400 to 500 concrete bridges statewide over the next five years.
The potential is significant for West Virginia, which has more than 6,700 bridges and ranks among the top 25 percent of U.S. states with significant bridge deficiencies.
West Virginia’s bridge problem is twofold, GangaRao said. “Number one, the state does not have the funds to rehabilitate all its old bridges. Number two, traffic intensity and load capacities have increased significantly since these bridges were built.”
“We have a lot of coal roads here,” he said. “While a typical 18-wheeler weighs only 72 kips [36 tons], a coal road bridge sometimes will carry 120 kips [60 tons] from a fully loaded coal truck. That is very hard on a bridge.”
How it Works
The technique begins by evaluating the bridge in situ—looking “at how much it has corroded, how much the concrete has spalled, and other aspects,” GangaRao said. “These evaluations can be based on very complex instrumentation or based on visual inspection.”
Next, GangaRao said, “we strip the bridge down to a solid portion of its original concrete or steel.”
West Virginia University
|Dr. GangaRao, a civil and environmental engineering professor and researcher, has been working on the bridge wrapping technique for 20 years.|
Finally, the structure is covered with a two-inch outer mortar cover and wrapped tightly with a material made from either glass fabric or carbon fabric and resin. The fabric gives the wrapping material strength, while the resin binds with the structure’s original substrate.
“Not only does it hold things together, but the wrap also enhances the strength of the overall structure,” GangaRao said. The wrap also offers protection from road treatments and weather.
Extending the Process
The Constructed Facilities Center trains private contractors and state highway workers on proper wrapping procedures, and those workers do most of the labor during refurbishing.
The CFC has wrapped some bridges itself, said GangaRao. “But most of these hundreds of bridges across West Virginia are being rehabilitated by private contractors using the process we developed here.”
CFC’s newest project, announced in late August, is the four-phase, nearly $1 million statewide bridge rehabilitation.
For that project, CFC will evaluate existing wrapping techniques, establish which state bridges are candidates for restoration, determine cost-effective design methodologies, and guide workers and contractors to learn the best wrapping techniques.
“I don’t decide which bridges get chosen,” GangaRao emphasizes. “There are certain load rating schemes that are followed, so there’s not a biased opinion about the end result.”
State highway engineers “look at each and every bridge once every two years, and they determine how much corrosion, how much spalling has taken place, what loads it can take, and other information,” said GangaRao.
“Then they determine if it is the right time to replace or rehab the bridge, depending upon the extent of damage or the deterioration. They call me when the structure gets very critical.”
GangaRao also directs the Center for the Integration of Composites into Infrastructure, a cooperative research effort by the National Science Foundation, industry and WVU. CICI’s mission is to accelerate the adoption of polymer composites and innovative construction materials into infrastructure and transportation applications.
Not surprisingly, GangaRao is a self-avowed “cheerleader” on the topic of material degradation—and a strong voice on the consequences of neglect.
“I think our infrastructure is going to deteriorate even more in the next five or 10 years, simply because we just do not have the money to keep pace with the rate of deterioration that’s taking place,” he said.
On Borrowed Time
“This might be due to the aging of the infrastructure, or it might be due to excessive use, or it might be due to the simple fact that our existing infrastructure has far exceeded its life expectancy as designed back in the 1950s,” he continued.
“For all these reasons, our infrastructure is going deteriorate at an even greater pace than we’ve seen in the recent past, because there are more vehicles, more tonnage—and the fact that, like human beings, materials and structures age. Therefore, once it goes beyond a certain life expectancy, the deterioration increases in its rate.”
In 2010, GangaRao said, deficient highways and bridges added more than $129 billion in costs to U.S. households and businesses.
He adds: “That’s why we should be concerned.”