Incorporating the Latest Materials With Sound Construction Techniques Promises to Reduce Bridge Life Cycle Costs
By Joseph L. Romano, P.E.

The I-95 Interchange at Scotch Road incorporates the latest construction materials along with sound and proven construction techniques with the goal of reducing the total bridge life-cycle costs while providing the public with a functional, aesthetically pleasing structure. The project is owned by the New Jersey Department of Transportation (NJDOT) and was designed by Arora and Associates, P.C. The interchange is located along I-95 where Scotch Road (CR 611) crosses over I-95 in the townships of Hopewell and Ewing, Mercer County, New Jersey.

The bridge, currently under construction, will be an approximately 300-foot-long, two-span, continuous structure. It will replace an older, functionally obsolete bridge and incorporates the latest advances in steel and concrete manufacturing. To increase the long-term effectiveness of these materials, the superstructure will be made continuous at the pier and will be supported at the ends by integral abutments. Therefore, the entire superstructure will be jointless and many of the problems associated with bridge deck joints, such as maintenance of bearings and rusting of steel, will be reduced. Eliminating deck joints also significantly reduces the chance of excessive corrosion and, hence, repairs to the girder ends.

The superstructure is comprised of unpainted high-performance steel (HPS) welded plate girders supporting a composite high-performance concrete deck slab. HPS is superior to conventional steels in that there is tighter control of the basic steel alloy elements that ultimately enhances the performance characteristics of the steel. Therefore, HPSs have better weathering, weldability, and toughness properties.

A high performance concrete (HPC) deck slab also will be used on this bridge. HPC structure is not new to the bridge construction industry. States such as Texas, Colorado, Virginia, Nebraska, Washington, New Hampshire, and New Jersey currently have bridges in service using HPC elements. Compared to conventional concrete, HPC has a decreased permeability to chlorides and other materials that can cause reinforcement to corrode. Arora and Associates and NJDOT engineers worked in cooperation to develop the specifications and design details for the newer materials used on this project.

Using pile-supported integral abutments reduces the initial and the total life-cycle costs. Labor and material costs are significantly lower with integral abutments than with conventional abutments. A further reduction in the initial cost was realized by reducing the span length and placing the pile-supported integral abutments behind mechanically stabilized earth (MSE) walls in lieu of full-height abutments.

A reduction in long-term costs can be realized through the elimination of the bearings at the abutments. Potential corrosion of the bearings at the pier also has been addressed. Although the deck is continuous over the pier, the potential for corrosion in the fascia bearings still exists because of their direct exposure to the weather. The interior pier bearings also are susceptible to corrosion because of the "up-splash" of moisture from the traffic below the bridge. To address this, steel drip plates, a common detail for use with weathering steel, have been welded above and below the bottom flanges of all girders to intercept water from being deposited on the pier cap and bearing area from the girders. These drip plates also aid in the prevention of substructure staining.

Weathering steels require no finished paint coating. This thin, protective coating of rust that forms on the girder shortly after fabrication and blast cleaning gives the girder a natural reddish- brown color and protects the steel from future corrosion. Using weathering steel eliminates the initial and future maintenance task of painting the girders.

When completed, the bridge will aesthetically complement this portion of I-95, which is located within a cut section that exposes the reddish-brown fracture shale common to the area. The use of unpainted weathering steel girders, decorative chain link fencing on the bridge, and selective pier-cap staining will complement the earth tones present in the area. In addition, the MSE walls in front of the integral abutments will have an architectural finish and also be stained to contrast yet complement the area.

The use of newer and more durable construction materials has an important role in reducing overall bridge life-cycle costs. However, the enhanced features of the materials and bridge elements have a better chance of performing as intended when they are incorporated with sound, cost-effective detailing and design techniques. The Scotch Road bridge intends to make this marriage a success. The construction of the Scotch Road and I-95 interchange began in the summer of 2001. The expected completion date is the summer of 2003.