If they had only chosen precast: experts propose precast as a solution for the troubled...

Summer 2004 was the summer of travel hell for many people in eastern Maryland. Time and time again, travelers heard the bad news on the radio. "The Chesapeake Bay Bridge traffic is ensnared in a massive back-up and has resulted in another delay," radio traffic reporters in Annapolis repeated

The 4.3-mile bridge connects Maryland's eastern and western shores. The bridge carries U.S. Route 50 east to west and U.S. Route 301, a major Washington, D.C. area north-south artery. It's the primary route for vacationers traveling from Baltimore and the nation's capitol to the Delaware, Maryland, and Virginia ocean resorts. Traffic congestion and jams occur at the slightest hint of trouble.

The William Preston Lane Memorial Bridge, known to many as the Chesapeake Bay Bridge, or simply the Bay Bridge, is actually two structures. The 38-foot-wide, three-lane, westbound structure was built in 1973. Alongside is the original two-lane eastbound span constructed in 1952. Neither bridge can be expanded to accommodate the ever-increasing traffic.

The Bay Bridge is a constant source of political grandstanding. For example, in an Aug. 11, 2005, Washington Post article, the Maryland Transportation Authority (MdTA) said that average weekday traffic is 61,000 vehicles. Weekend daily traffic is even worse, reported at 95,000 vehicles. Along with the traffic flow comes delays. MdTA officials say that on especially heavy days, delays can last for up to six hours.

Maryland Gov. Robert Ehrlich told the newspaper, "Finding a solution to the growing traffic congestion and needs at the Bay Bridge is essential if we are to continue to thrive as a state." With so much on the line, a task force was charged with developing a solution.

This environment generated a strong public outcry after almost two years of extended delays. Some locals suggested that the overlay project's problems began at the beginning. A report from a blue-ribbon panel of experts shows the repair project seems to be a classic story of a good idea applied improperly.

Haste makes waste

Given the potential for public up roar when lane shutdowns would be too long, engineers from MdTA and managers from the Cianbro Corporation, the Baltimore-based contractor with more than 55 years of road building experience, needed this project completed as quickly as possible. MdTA wanted the work to be completed outside the summer season, outside of peak hours, and with only one lane closed at a time.

The contractor began work in the spring of 2002. Cracks in the overlay first observed in December 2003 became a significant problem by the following spring. Sensing a major problem, MdTA instructed an overview team to find the engineering causes for the failure and to present solutions. The team consisted of Thomas Deen, John Milliron, Mary Lou Rails, and Henry Russell. All were experts in concrete and bridge construction.

In January 2005, the overview team, with help from others, submitted a report on the bridge deck failure to MdTA. In it, they examined the entire project from concept to execution.

"Measures to expedite production on the job contributed to critical weaknesses in the overlays that were constructed," the group stated.

The key problem was the overlay delaminated, or separated, from the substrate. "The delaminated overlays did not have the ability to contribute fully to the deck's load- carrying capacity," the report states. "Cracking in the overlays spread rapidly."

The task force identified six interrelated factors that contributed to the failure of the interface between the overlay and the substrate:

* The thin deck resulted in higher than normal shear stresses at the region of the interface.

* Inadequate surface preparation of the top portion of the substrate weakened its ability to form a strong bond with the overlay.

* The matrix restorer, an epoxy material applied to the substrate, diminished the bond strength of it to the overlay.

* Using a concrete mix design with silica fume resulted in slow strength gain during the cold weather construction periods.

* Since much of the construction occurred during cold weather, low curing temperatures may have slowed the concrete's strength gain. The bond between the overlay and the substrate may have been weakened by traffic that was allowed on the bridge too early.

* Using a sprayed curing compound may have further slowed the concrete's rate of strength gain, increasing susceptibility to damage by traffic.

Precast to the rescue

Given the concerns about the quality of the overlays, many experts believe it's only a matter of time before motorists will face another round of repairs. The investigators suggested this as well in their report. "It is prudent to begin now to assess the range of state-of-the-art options available and to design a strategy for full-depth replacement when needed," they said.

One the responsibilities of the task force was to advise MdTA on construction methods that would repair the bridge deck, while minimizing the effect on traffic. "Except for limited replacement, cast-in-place concrete deck options should generally be considered a last resort on the Bay Bridge," the report stated.

The report outlined several successful bridge deck repairs on which prefabricated systems were used. These successful projects include the Tappan Zee Bridge on the New York State Thruway, the Lewis and Clark Bridge over the Columbia River between Washington and Oregon, and the Jacques Cartier Bridge over the St. Lawrence River in Montreal, Quebec.

Engineers working on these structures faced similar challenges to those on the Bay Bridge. Using similar solutions could have made life easier for thousands of Maryland drivers.

The author is a freelance writer for newspapers, magazines, and Web sites in Maryland who spends maw hours stuck in traffic on the Chesapeake Bay Bridge.

For a report on prefabricated bridge projects, visit the U.S. Department of Transportation's Federal Highway Administration at www.fhwa.dot.gov/bridge/prefab/.