Officials at the Maine Department of Transportation needed to quickly replace the 60-year-old Bath Viaduct on U.S. Route 1, which spans surface streets and a railway. To achieve their goal for smoothing summer traffic, they created a design-build, incentive-laden contract with a deadline of 220 days, versus the 720 days it took to construct the original bridge.
The project required demolishing the original 20-span structure and constructing a new 1,300-foot viaduct as well as modifying one abutment, adding drainage, and replacing a railway crossing at the intersection.
To meet this rapid timetable, designer VHB and contractor Reed & Reed incorporated a variety of Accelerated Bridge Construction (ABC) techniques into their plan. Foremost was the use of precast concrete New England Extreme Tee D beams, which include a topped flange that serves as the wearing surface, eliminating the requirement to have secondary castings done in the field, reducing on site tasks, and schedule durations.
The viaduct features 20 spans, encompassing 80 NEXT beams in all. The beams were cast with 8,000-psi concrete requiring a release strength of 6,000psi. This requirement would normally create challenges for a precast producer especially achieving this on a daily basis, notes Andrew LeVatte, from Strescon Limited, the precast producer.
“As soon as we secured the contract and shop drawings were approved, we jumped into casting the NEXT beams,” he says. “We poured, cured, and stripped the beams every day. Achieving the 7-day release strength of 6,000-psi concrete in 18 hours, never losing a day of production”.
Precast Prestressed bridge beams naturally camber once the prestressing force applied to the prestressing strand is transferred into the concrete. In order to compensate for this, VHB Engineering calculated the amount of camber in the beam then adjusted the concrete thickness of the driving surface as it approached the beam end essentially creating a flat driving surface.
The NEXT beams, four per line, are 8’4” wide, with span ranging from 60 to 70 feet long and 75-foot spans over the rail tracks. The beams had rebar for deck curbs installed on fascia beams upon arrival at the site. The beams were unloaded with a 250-ton Manitowoc 999 crane and erected by two 150-ton Link Belt cranes. The beams were set, a pour strip was applied, and they were covered with a membrane and topped by a 3-inch wearing course.
The beams were manufactured throughout the summer and early fall and were ready for delivery through the winter. The existing foundations were reused to save time and material, and 19 hammerhead piers and pier caps were cast by Reed & Reed crews near the site, as they were too cumbersome to transport to the site, Lavatte says.
Traffic was detoured during construction and crews worked both day and night shifts to speed construction. Precast components arrived steadily and were quickly erected. In fact, the project beat its deadline of Memorial Day weekend in 2017 by nearly one month, maximizing the incentive payment.