Opened on July 11, 1936, at a cost of $60 million, New York City's Triborough Bridge carried approximately 30,000 vehicles per day between Queens, Manhattan, and the Bronx during its first year of operation. Today the bridge—actually a complex of three long-span bridges and related facilities—carries 200,000 vehicles a day on eight lanes of traffic. To maintain this critical link in New York's transportation system, the Metropolitan Transportation Authority's bridges and tunnels division began in 1997 a multi-year, $550 million program to renovate the bridge.
This massive reconstruction project was divided into three phases and let in a number of sections with a completion date of 2009. The Queens' section—part of phase one and now nearing completion—involves a $150 million full deck replacement project awarded to American Bridge Koch Skanska—a joint venture between American Bridge Corp., Coraopolis, Pa., and Koch Skanska, Carteret, N.J.
The suspended portion of this bridge consists of 250,000 square feet of an orthotropic steel replacement deck system. The steel panels are pre-formed at about 10 feet wide—the width of one road lane— and weigh about 15 tons each. An additional 175,000 square feet of precast concrete panels also are used for anchorage and viaduct decking.
In addition to deck replacement, the contractor is responsible for replacing barriers on the bridge with 28-foot-long galvanized steel median barriers. The barriers are assembled as modules with two median barriers welded down to each steel deck panel. This creates a new design offering additional room for traffic.
Bloxide Protects the Sections
As delivered, the steel deck panels are covered with a temporary coat of grit-filled epoxy for protection and traction. This epoxy coating must be shot-blasted off before the barrier modules can be welded to the deck panels. Galvanization in the weld area of the median barriers also must be ground down to bare metal to allow for a clean weld. After this preparation, the deck is power-washed and a coating of Bloxide—an aluminized rust preventative weldable primer—is rolled on the deck. The barriers then can be permanently welded to the deck without the need to remove the Bloxide coating.
Engineers at American Bridge Koch Skanska chose Bloxide—a proprietary primer manufactured by Tempil of South Plainfield, N.J., an Illinois Tool Works company—to fill several needs. It protects the weld areas of the massive deck sections and barrier modules before welding, improves weld quality, and serves as a protective coating to avoid corrosion through years of use, since the sections will be semi-exposed after the barrier modules are permanently welded to the deck panels.
Bloxide Use and Properties
The rust-preventive coating protects surfaces and prepared edges from rust, eliminates cleaning of rust prior to welding, and is excellent for extended periods of outside steel storage. In the welding process, it allows striking a welding arc without removal, protects the weld pool, and leaves no inclusion residue or slag. Aluminum in the primer acts as a scavenger in the weld pool and reduces porosity and pinholing, assisting in achieving high-quality welds (evaluated by X-ray).
Bloxide is effective on all steels, including high-tensile, carbon moly, and chrome moly, and acts as a primer for paint and other coatings. It is applied at temperatures above 50° F by brush, dip, or spray and resists temperatures up to 800° F.
One gallon of Bloxide covers approximately 800 square feet. To achieve longer protection and adequately cover the coarse, shot-blasted steel, the product was applied at a greater thickness on the Tri-borough Bridge project than the standard 0.75 mil dry thickness. On the Triborough Bridge, about 20 to 25 gallons of Bloxide was used to cover 7000 square feet.
— Jon Hart is a project engineer with American Bridge Koch Skanska, a joint venture.