Precast panels help NYSDOT make emergency bridge repairs without shutting down a major artery into New York City.
By Bridget McCrea
It was mid-2001 and the more than 190,000 vehicles that used the inbound lane of the 3.5-mile-long Gowanus Expressway into New York City every day would soon be traveling on a new bridge deck. Precast concrete Exodermic panels, a licensed product that was to be instrumental in completing the redecking project quickly, were ready and waiting to be installed. But then tragedy struck.
The project, having just begun in 2001, was promptly shut down after the terrorist attacks of Sept. 11. “When 9/11 hit, it literally stopped us in our tracks,” says Robert Harding, vice president and chief engineer at Whitestone, N.Y.-based Grace Industries, the project contractor. “We were in the process of getting everything ready to do this major project, and suddenly everyone’s attention had to shift to more pressing matters.”
A yard full of the precast Exodermic panels began to gather dust at Downingtown, Pa.-based Faddis Concrete Products, waiting to be installed on the bridge. Because the appalling events unfolded in the Gowanus Expressway’s own back yard, it would be at least a year until the project would resume.
“At the time, we didn’t know when we were going to start back up again,” recalls Harding. “It didn’t hurt the project, but it definitely prolonged it.”
Owned by the New York State Department of Transportation (NYSDOT) and built in 1941, the bridge serves as the southern extension of the Brooklyn-Queens Expressway and has been identified by the American Automobile Association as one of the most congested highways in the United States.
In the early 1990s, NYSDOT began looking at ways to update and improve the bridge, with one of its major initiatives being the redecking project. According to Harold Fink, director of the Gowanus Expressway Project for NYSDOT, the redecking is part of a larger plan to improve the Expressway, which – after 60 years of heavy use – had outlived its useful life and was in need of an overhaul. Fink says the bridge deck was in the poorest condition, with “punch-throughs” showing up along the structure. “It was a pretty serious issue,” recalls Fink. “To address it, we generally use an emergency repair contract about every 18 to 24 months and basically maintain a constant presence out there.”
To reduce the time it would take to install the new decking, NYSDOT engineers specified precast Exodermic panels for the repair. Grids for the panels were produced by American Bridge under subcontract from LB Foster, and Faddis Concrete Products and Grace Industries manufactured the panels. According to Fink, the selection allowed NYSDOT to limit bridge shutdowns to weekends, when traffic in and out of New York City is much lighter.
“We had to do the work on the weekends and not impact peak weekday traffic,” says Fink. “By using precast, we were able to do two spans each weekend.”
Time is of the essence
Harding says NYSDOT’s plan was to demolish a section of the bridge deck on a Friday night, replace it with the precast panels and have the bridge reopened by Monday morning. He says precast was the best choice, since it required no mass curing that a poured-in-place structure would require. Breaking out the existing concrete, building the new forms, installing the reinforcing steel and pouring a bridge in the conventional manner requires a minimum 28-day curing time – time that the NYSDOT couldn’t afford when it came to the heavily traveled Gowanus Expressway.
“It’s one of the most important arterial roads into Manhattan, and they just couldn’t afford to shut down a section of it,” says Harding.
Once the panels were ready for installation, Harding says the companies handling the repairs launched a frantic Friday-through-Sunday schedule to get them in place for Monday morning’s rush hour. Load limitations on the antiquated bridge made the work tedious, says Harding, mainly in terms of setting up cranes. “They had to be positioned very accurately to make sure the structure stayed safe,” he explains. “We used a variety of load-transfer beams to set up the cranes, and had to factor in weight and other issues before bringing them up.”
Every Friday for the next few months, the crew would set out on a routine of breaking out the old decking, taking care of any structural repairs that needed to be made and prepping the work site for installation. On Saturday, the panels were installed using a crane with a six-point lifting apparatus to avoid damaging the panels. “We had to jack them up a bit to bring them to the proper elevation,” says Harding.
Gary Figallo, production manager for Faddis Concrete, says the handling of the panels was critical, particularly when it came to the arrangement and delivery methods. While NYSDOT had the project on hold after 9/11, for example, he says Faddis Concrete stored the panels three deep in a flat, planar condition to avoid damaging them. During installation, he says the panels had to be handled flat to avoid any stresses such as twisting, which could lead to cracking.
“The panels had to be cast, handled, delivered and installed flat,” says Figallo. “Once they were installed, they were fine.” At the beginning of the project, the precaster set up rigid form decks for clamping down the grids prior to placing the concrete. “We were aware that the heat of the hot-dip galvanizing had warped the grids on prior projects, and that sweep (horizontal curvature) would be the most difficult dimensional error to deal with,” Figallo explains. “As it turned out, only one deck was rejected for having (excessive) sweep.”
In between the panels, where they rested on the beams, Harding says the contractor used rapid-setting concrete, which has a cure time of two to three hours. By Monday morning, the four to five panels were installed and ready to accommodate the heavy New York City commuter traffic, save for the longitudinal diamond grinding necessary to even out the high and low spots, which was performed at the end of the project. Four days later, the routine started again and continued until all 120 panels were in place.
No one likes road delays, particularly those who must navigate congested areas like New York City. That is why NYSDOT invested a little extra money for precast panels that could be installed when needed, without disrupting traffic flow. By selecting precast, the state also got a high-strength concrete in a mix that was carefully controlled in a plant setting, rather than out on the roadway.
“All kinds of problems can come up when you’re trying to deliver a very high quality concrete to a job site,” says Figallo. “There can be traffic delays, problems with the mixer, operator error with the mixer and issues like too much water in the mix. With precast, we were able to control the quality, which should lend itself to a more durable, longer-lasting product.”
Despite the scheduling delay, Fink says NYSDOT is “99 percent satisfied” with the project’s outcome, though he says the state has noticed minor leaking at the joints between the precast panels where the rapid-setting concrete was used. “There’s been leakage at the closure pours,” says Fink. “It’s not a serious leak, but we are concerned about that.”
Figallo points to the bridge’s structure as the culprit. The substructure is supported by steel beams, he says, and the precast elements are interrupted at those points. “After the grid is put in place, they weld something onto the top of the steel beam called an elephant stud, and that provides the connection between the new decking and the existing structure,” says Figallo. “Rapid-setting concrete was used at the closure pours and is keyed into the precast to provide a structural connection. Apparently some of those are not watertight.”
Harding says the time saved to the traveling public was a good tradeoff for the extra cost paid for the precast panels over the poured-in-place option. “Your really can’t put a cost on it,” says Harding. “Our projects are extremely sensitive to commuters. While we would love to shut down the road and do it during the day, we can’t because it would slow or even stop the commerce coming in and going out of New York City.”
Project: Gowanus Expressway, New York City
Owner: New York State Department of Transportation
Engineers: Charles H. Sells Inc., Briarcliff Manor, N.Y., and NYSDOT
Contractor/Installer: Grace Industries, Whitestone, N.Y.
Precast Manufacturer: Faddis Concrete Products, Downingtown, Pa.*
* Faddis Concrete Products is a certified plant under NPCA’s Quality Assurance/Plant Certification Program.