When Connecticut highway officials designed the Merritt Parkway in the 1930s, they saw an opportunity to create a different experience for America’s growing legions of auto drivers. First conceived to relieve congestion on the old Boston Post Road that crawled through the coastal towns, the Merritt broke new ground in highway design: It was one of the first highways to be routed away from busy downtowns, one of the first to prohibit truck traffic and one of the nation’s earliest limited-access highways.
But it is perhaps best known for its landscaping and its bridges. The Merritt’s unusually wide right-of-way is carefully landscaped to hide adjacent parcels of land, creating a sense that drivers are making their way through a vast park that stretches from the New York state line almost to New Haven. The original concrete bridges—each with a unique Art Deco design—still carry cross traffic over the highway.
The parkway notion caught the imagination of highway planners across the country, and these design principles were copied with greater and lesser degrees of success throughout the country. Still, few attained the grace and beauty of the original Merritt Parkway, which was named to the National Register of Historic Places, a distinction usually reserved for historic buildings and battlefields.
After the Merritt was completed as far as the Housatonic River near Milford, Connecticut highway officials broke ground on a new parkway—the Wilbur Cross—that would extend nearly to Hartford. Originally, plans called for parkways all the way to the Massachusetts border, a plan that was overtaken by development of the Interstate Highway System. Today, the Wilbur Cross feeds into the Berlin Turnpike north of Meriden.
If there was one piece of the puzzle that didn’t quite fit into the parkway vision, it was the Sikorsky Bridge, which spanned the Housatonic River, connecting the Merritt and the Wilbur Cross.
It was a stepchild. Officially, it wasn’t part of either parkway.
And it certainly didn’t fit with the Merritt’s design principles. Still, feeling the lingering effects of the Depression and with the threat of war on the horizon, Connecticut officials were more interested in saving time and money than in highway aesthetics. Opened in 1940, the bridge was a utilitarian steel structure with an open-grid steel deck. The cost was $1 million.
High, shoulderless and narrow-laned, the Sikorsky Bridge was unloved by drivers, who dreaded driving over the slippery decking, especially during wet or icy weather.
Nearby residents didn’t care much for the Sikorsky, either. They considered it an eyesore, and the open-grid decking allowed the water below to reflect traffic noise.
In 1989, a reconstruction project replaced support stringers, retrofitted pin-and-hanger assemblies and refurbished the deck, but it didn’t do much for drivers or residents.
In fact, the new grid, which contained slightly larger studs, greatly increased vibration and noise.
Even with additional repairs, engineering studies concluded that the bridge needed to be replaced for a number of reasons, including the inability to replace the open deck with a solid deck that would have adequate shoulders to carry current traffic.
Old with the new
Given the history of the Parkway, the concerns of nearby residents and complaints from drivers, the Connecticut Department of Transportation (ConnDOT) understood that replacing the Sikorsky Bridge would be no ordinary highway project.
It invited community input into the project and worked with the Merritt Parkway Advisory Board, representing various public entities and department officials, to contribute to the final design of the new bridge.
Recognizing that the bridge is the gateway to the Merritt Parkway, designers created a bridge that reflects the Parkway’s traditions, but with some modern-day updates. The new Sikorsky Bridge incorporates a bikeway/walkway on the deck, offering unobstructed views of the Housatonic and connecting with bike paths and trails on both sides of the river. Designers added a variety of architectural details, including stylized parapets, classic-style fencing and decorative lighting on pylons at the piers and abutments.
The bridge gets high marks for sustainability as well.
Fly ash and silica fume significantly reduce the embedded energy of the concrete used in the reconstructed bridge deck. While cost and performance considerations were the primary reasons for using these materials, the environmental benefits are in line with the project’s goals and the community’s values.
All innovation on deck
The final design called for a five-span continuous bridge, with variable-depth steel girders and a high-performance concrete (HPC) deck.
In November 2000, the contract was awarded to Balfour Beatty Construction Inc. of Atlanta, Ga., for $83.7 million. In November 2003, the first span opened and traffic was shifted to it, clearing the way for the old bridge to be demolished. Work was expected to be completed in December 2005.
When complete, the bridge will be capable of handling 41,000 vehicles per day.
The new spans are approximately 600 meters long. The eastbound span is 18 meters wide, with two traffic lanes, one operational lane and full 3-meter shoulders on both sides. The westbound span is 22 meters wide, configured the same as the eastbound lane but with the addition of the 3-meter-wide walkway/bikeway.
Three concrete piers are supported on 2-meter-diam. drilled shafts, socketed into the bedrock approximately 25 meters below the river bottom.
The land-based pier on the east end of the structure is set on bedrock. The piers are constructed of a combination of class 40 and class 50 concrete. Minimum cement content was 390 kg/cu meter, with 15% Class F fly ash replacement of portland cement, which contributes to decreased permeability.
Special attention was given to the construction of the deck. To address the longstanding complaints about noise, a solid concrete deck with an asphalt overlay was used.
To reduce maintenance requirements, the deck uses HPC, employing Lafarge SF Cement and fly ash. Lafarge SF Cement is produced by blending (intergrinding) 92% portland cement and 8% pelletized silica fume.
One of the most critical considerations for the deck was permeability and its impact on service life. Because of the high traffic volumes over the bridge, durability is especially critical to minimize disruptions and lane closings. The Lafarge SF Cement reduces permeability of concrete by creating a denser cement matrix compared with conventional concrete. The silica fume in the cement is made up of spherical particles 100 times finer than those of an average particle of cement. The blended cement also modifies the paste structure around aggregates and other embedded items, significantly reducing bleeding of the concrete during hardening.
Projected service life for the HPC deck is 75 years, compared with 40 years for a standard deck, according to ConnDOT’s life-cycle cost analysis.
The HPC deck is overlaid with a woven-glass membrane and topped by hot-mix asphalt for added protection. The membrane prevents water and chloride penetration into the concrete.
Bulk, bag or blend?
As in Connecticut, many highway departments across the country are specifying HPC for critical projects. It yields environmental and economic dividends in terms of reduced maintenance requirements, fewer traffic tie-ups and extended service life.
As HPC specs become more widespread, producers are thinking hard about how to meet these specs without disrupting their existing operations.
For silica fume, producers have three options: bulk, bagged and blended cements. Because of the fineness of the material, bulk silica fume can be tricky to handle, especially during transfer from truck to silo. Also, the producer must dedicate an entire silo to the material, which adds to the capital and inventory costs and makes the silo unavailable for storing cement.
Bagged silica fume poses challenges as well. Labor costs are increased when workers have to physically add bags of silica fume to the truck. Quality control becomes more difficult—workers can forget to add the bag to a load, the mixer may not completely distribute the silica fume through the mix or bags may not disintegrate completely.
Blends offer several advantages for producers. Producers can keep the silica-fume blend on hand for projects requiring high performance but also can use it on other jobs if portland cement supplies run low. What’s more, the blended cement makes it easier for producers to supply other customers with an HPC when it’s needed.
Beard Concrete, Milford, Conn., supplied the concrete for the Sikorsky Bridge reconstruction. It was the company’s first major job involving an HPC spec, said owner Jim Beard, and he chose to use Lafarge SF Cement, combining it with fly ash at the plant.
“Bags weren’t really an option because of the size of this project,” he said. “And we didn’t want to get into blending silica fume and portland cement at the plant. It’s much simpler to use the blended cement: We handle it just like portland cement—we add the fly ash and we’re ready to go.”
The blended cement offers a high degree of consistency and quality control. But for Beard, the key consideration was simplicity. “The proportions are preset. It takes any guesswork out of the process. And from an operational standpoint, using the blends is just like using portland cement. It keeps things simple.”
The new Sikorsky Bridge fulfills the vision first laid out for the Merritt and Wilbur Cross Parkways: A graceful span, in harmony with the still-idyllic right-of-way and sensitive to the ecology of the region.
