Maryland officials said yesterday that they are baffled about why a special type of concrete used on other bridge projects failed on a recently repaved section of the Chesapeake Bay Bridge, a problem that could cost $7 million to fix and promises to delay traffic for months.

The section lies along two miles of one of the westbound lanes of the bridge, where a four-year, $60 million construction project to remake the span is a little beyond its halfway point.

State Transportation Secretary Robert L. Flanagan said that two inches of concrete were scraped off the road surface, and when a different type of concrete was poured onto the road, it did not bond and began to crack.

A consultant has been hired to figure out whether fault lies with the state, the project's engineer or the construction company.

Whatever the cause of the problem, it is certain motorists can expect more delays along Route 50.

State officials said drivers, who have been sitting in construction-related backups for nearly three years, should expect "major delays and congestion" on the bridge this fall because the left lane of the westbound span will be closed until Nov. 24. Additionally, two lanes will be closed nightly starting at 8 p.m., and all three will be shut down from 10 p.m. until 5 a.m. During those hours, two-way traffic will run on the eastbound span.

State officials said they used a type of material, called microsilica concrete, that allowed them to do work on the bridge during the cool spring and fall months. They said they avoided summertime work so they would not add to heavy delays that come from Eastern Shore beach traffic. The winter is too cold for such work.

Microsilica is much finer than regular cement particles, which makes it denser and stronger. But the process to mix it is also more delicate, and if not done properly, the concrete can shrink and crack, according to construction experts.

Nonetheless, they said, it's a widely accepted technology that several states use. "Microsilica has been used across the country successfully over a million times," said Scott Haislip, director of streets and local roads at the American Concrete Pavement Association. "There's no reason with proper protection" it could not be installed in any type of weather, he said.

Maryland officials said they had confidence in the substance because it had been successfully used in similar circumstances on two other bridges, both on Interstate 895.

A spokeswoman for Cianbro Corp. said the fault does not lie with the Pittsfield, Maine-based construction firm. "We did perform the work per the contract specifications," Dottie Hutchins said. Calls to Wallace, Montgomery & Assoc., the Baltimore engineering firm responsible for the project design, were not returned.

Flanagan has hired Hal Kassoff, former head of the State Highway Administration, to lead a commission to figure out how to fix the bridge. Kassoff said he planned to meet with Flanagan this week to form a strategy but was unsure of solutions.

"I can't say it's impossible to work in the cold weather," said Kassoff, an employee with the engineering firm Parsons Brinckerhoff. "But that technique didn't produce the results."

Virginia endured a major construction problem last year when a 21/2-mile stretch of Interstate 64 had to be torn up and repaved after engineers discovered that it had been improperly graded and could be hazardous during rainstorms. That cost the state $2.7 million.

In Maryland, Democrats in the legislature criticized transportation officials in the Republican administration of Gov. Robert L. Ehrlich Jr. and promised increased oversight.

"We will definitely have hearings on this, in both the Senate and House," said Del. Peter Franchot (D-Montgomery), chairman of the House appropriations subcommittee on transportation. "There are generic questions of competence and just overall ineptness."

Franchot also criticized the idea of forming an outside commission.

"I don't think we need to sugarcoat this situation with some kind of blue-ribbon commission," he said. "They obviously made an error. They just need to admit the error and move forward."

After three years of construction-related backups, even more congestion is ahead.Use of the denser and stronger microsilica concrete allowed bridge work during the spring and fall. Summertime work was avoided so it would not worsen Eastern Shore beach traffic.