As our nation's bridges come under increasing scrutiny, New Jersey agencies are taking action. At issue was bridge safety for two deteriorating spans in high traffic areas. The challenge was to maintain the historic character of the two bridges while updating them to current safety standards. The engineering firm of French & Parrello in Wall, NJ, met this challenge head on with advanced concrete technology that garnered the firm awards for both projects by the New Jersey chapter of the American Concrete Institute (NJACI) and the New Jersey Concrete and Aggregate Association (NJCAA).
The first bridge is a NJ Department of Transportation span on Route 202 over Mine Brook in Bernardsville Borough. It was a concrete arch bridge in a rural, but highly trafficked, area. Local residents wanted the replacement bridge to replicate the original as much as possible.
"Initially, we were considering staged construction for replacement of the bridge," said Michael Troncone, P.E., Transportation Department director, French & Parrello. "But that would have had tremendous environmental repercussions. It would have required temporary widening and the cutting down of numerous trees, wetlands impacts and filling within a flood plain. Therefore, we had to close the bridge and detour the traffic."
In order to minimize these closures, French & Parrello turned to precast concrete. The bridge was designed using precast inverted T-sections. Small cast-in-place closure pours in the footings were used to lock the precast sections together. Stone veneer from a local quarry was used on the exposed surfaces of the bridge to create the historic look.
The NJDOT required the project to be completed within nine weeks. The actual installation of the precast concrete took only a few days. The remainder of the time was for aerial utility relocations, road construction, drainage, grading, and placement of the stone veneer.
"The contractor finished three weeks ahead of schedule due to the decision to work with precast concrete," acknowledges Troncone.
The second bridge is a 67-foot span on East Cliff Street over Peters Brook in Somerville Borough. The original bridge featured concrete balustrades within the parapets and on the arch. While the concrete slab arch had only minor spalling and some exposed reinforcing steel, the spandrel walls were bulging and leaking water. The challenge here was to replicate the architecturally significant balustrade parapets.
"It became apparent that concrete had to be used on this project," explains Troncone, "so that the finished result would replicate the original bridge without indicating that it was rehabilitated."
French & Parrello called for the removal of the original spandrel walls and installation of an anchor slab that was doweled into the top of the arch. Designers then called for pouring of new spandrel walls in front of the anchor slab. On top of the wingwalls and the new spandrel walls, the contractor placed a parapet that incorporated precast balustrades, precast planks and cast-in-place railing and pylons that replicated the look of the original bridge. A calcium nitrate-based corrosion inhibitor was added to the cast-in-place concrete to increase the service life of the rehabilitated concrete bridge components.
Also included in the work was rehabilitation of the arch extrados. A cement mortar parge coat was spread over the arch, and a membrane waterproofing applied. Porous fill (No. 8 broken stone) was used to fill the space above the arch to support the road bed.
Three different types of concrete repairs were also performed at various locations along the arch intrados and on the front face of the wingwalls. Quick-setting, non-sag patch concrete was used to repair surface scaling, concrete spalls and areas with exposed reinforcing steel. The team coated all exposed exterior surfaces with a flexible acrylic skim coat for a smooth, uniform appearance.
"A very valuable feature of concrete is that it can be formed in any shape desired," said Troncone. "These projects validate the fact that concrete can be used to incorporate aesthetics in bridge design."
For the first bridge, French and Parrello utilized 58 cubic yards of NJDOT Class A concrete, 212 linear feet of abutment and wingwall units, and 53 linear feet of culvert units for a cost of $1,242,421. For the second bridge, the firm repaired 995 square feet with 92 cubic yards of concrete plus 460 square yards of mortar parge coat. There was also 147 linear feet of balustrade railing.
The innovations in both bridges earned French & Parrello recognition by the concrete industry at the NJACI and NJCAA annual awards.
"We are pleased to be honored for these projects, which will ultimately make those areas in New Jersey a better place to live," said Argo Parrello, president and CEO of French & Parrello.
The NJACI is an active organization of approximately 500 members who strive to further education in concrete technology throughout the state of New Jersey. Members include contractors, engineers, educators, concrete and concrete material suppliers, manufacturers of concrete-related products, and testing laboratories. For more information, visit www.njaci.com.
The NJCAA represents their members in areas of legislation and technical consultation. The group promotes the concrete and aggregate industry.
Editor's note: French & Parrello is a multidisciplinary engineering firm with two offices in New Jersey and one in Pennsylvania.