Virginia Highway Project Boasts One of the Country's Biggest Bridges
Virginia Highway Project Boasts One of the Country's Biggest BridgesPump equipment is key to the first of four massive concrete pours
The Pocahontas Parkway is a new $324 million highway project under way outside Richmond, Va. The 9-mile (14.5 km) roadway is one of Virginia's most highly visible construction projects for two reasons. Not only is it the commonwealth's first public-private construction project, but also at the end of the parkway will be one of the longest cast-in-place segmental bridges in North America.
The project, also known as the Route 895 Connector, has been one of the area's top transportation priorities for 15 years. When completed in 2002, it will provide a new link with the Richmond International Airport and a route for 20,000 vehicles a day traveling to the southern and eastern portions of the city.
The Pocahontas Parkway is the first construction project implemented under Virginia's innovative Public-Private Transportation Act of 1995. The Act was created to accelerate transportation projects that would otherwise sit waiting for state or federal funds. For this roadway, more than 90 percent of the funding is from special tax-free bonds sold to private investors – who will be repaid by tolls collected from commuters.
The project is being developed and constructed by FD/MK LLC, a joint venture between two global engineering and construction firms, Flour Daniel and Morrison Knudsen.
David Wesson, Virginia Department of Transportation (VDOT) project manager, said the four-lane highway is a complex project. In total, it requires construction of 20 new bridges over rivers and existing highways. (The parallel road design requires two bridges at each crossing.)
The largest structure will be a new 4,765-foot (1,452 m) bridge that stands nearly 150 feet (45 m) above the James River, enabling ocean-going vessels to access Richmond's deepwater terminal. The bridge's 673-foot (205 m) clear span will be the third longest cast-in-place structure in North America.
The concrete construction phase for the James River bridge began this fall. To date, this phase of the project has used more than 5,000 cubic yards (3,823 m3) of concrete. This volume will double when the second footing is completed in October.
Before the first of four massive footings were poured, two sets of 10 concrete-filled caissons were constructed to anchor the footings to bedrock. The 8-foot (2.4 m) diameter caissons extend 60 to 80 feet (18 to 24 m) down and contain approximately 120 cubic yards (92 m3) of concrete. Then Hydracrete Pumping Ltd. got involved.
Four 24-hour concrete pours
Charles Jenkins, branch manager for Hydracrete, the pumping contractor, brought in Putzmeister equipment to pour the first of four enormous above-grade footings that anchor major bridge support columns.
The footings are each 80 by 90 feet (24 by 27 m) wide, by 16 feet (5 m) tall. Each contains 350 tons of rebar.
Due to the mass of the structures, VDOT required a special concrete mix to lower the concrete temperature and slow the drying time. The 4,350 psi (30 mpa) mix contained 75 percent NewCem, a ground blast furnace slag, and 25 percent Portland cement.
Don Ross, project engineer for Recchi America, Inc., one of the joint general contractors, said the mix worked well. The core temperature maintained a 155-degree (68.31/4 C) maximum – well below the 170-degree (76.61/4 C) VDOT requirement. The footing temperature was monitored with thermocouples placed at 6-foot (1.8 m) intervals in the center of the pour.
The $324 million Pocahontas Parkway is one of Virginia's most highly visible construction projects. Not only is it the commonwealth's first public-private construction project, but also at the end of the highway will be one of the longest cast-in-place segmental bridges in North America. Contractors used two Putzmeister pumps and a Telebelt for the critical "Phase Two" concrete pours
To place the 4,050 cubic yards (3,096 m3) of concrete for the first footing, four 28-man crews were needed. Two Putzmeister concrete boom pumps – a 36- and 42X-Meter – and a Telebeltâ TB 105 conveyor were used to deliver the concrete in a continuous 24-hour pour.
Ross said the boom pumps were obvious choices. And after seeing a video on Telebelts, he decided to give the TB 105 a try. "With the belt's high output, it's ideal for these huge pours," said Ross. "In fact, it delivered about 50 percent more concrete per hour than the pumps." The TB 105 has a maximum output of 360 cubic yards of concrete per hour.
In addition, he said that the bridge is a tough job site. The footings are wedged next to the river. Eight 40-foot (12 m) tall rebar towers are in the middle of the structures. Plus, Hydracrete had to place the tremie hose down through the rebar to a crew working inside the 16-foot superstructure for much of the pour. "We had to move the equipment several times an hour to place the mud," he said. "So we needed all three machines and almost 24 hours to finish the job."
Jenkins, a 24-year concrete veteran, said they probably put a week's worth of wear on the equipment in a single day. "The pumps worked great. We were placing a tight, 2- to 4-inch (50 - 100 mm) slump mix in 2-foot (0.6 m) lifts [sections]." He added, "These Putzmeister pumps have higher output and head pressure than other units. We ran them without any hydraulic temperature or pressure problems." Both the 36- and 42X-Meter pumps have 210 cubic yard (160 m3) per hour outputs.
The 4,765-foot (1,452 m) bridge will stand nearly 150 feet (45 m) above the James River, enabling ocean-going vessels to access Richmond's deepwater terminal.
In fact, Jenkins and Mike Carr, Hydracrete's vice president, said the company has been adding to its fleet of Putzmeister equipment over the last three years. "I bet we bought $1.5 million worth of PM pumps and belts this year," said Carr. "The equipment does what it says it does."
Ross said the contractors are using the Putzmeister boom pumps to pour the 90-foot (27 m) concrete support columns that are anchored in each footing, too. VDOT specified the same 4,350 psi (30 mpa) concrete mix for the 8- by 32-foot (2.4 by 9.8 m) columns and caps. The columns will be cast in place with jump forms in 30-foot (9.1 m) lifts.
Above the columns will sit both 15-foot (5 m) pier caps and 40-foot (12 m) pier tables. The bridge deck sits on the tables. VDOT specified a 6,500 psi (45 mpa) concrete mix for the bridge deck.
The main span superstructure (crossing the river) will be cast-in-place segmental box girders, and will be constructed in balanced cantilever with form traveler and post tensioning.
The east and west approach superstructure will be precast concrete segmental box girders, also constructed in balanced cantilever. A major portion of the ramps will be precast segmental concrete box girders, constructed span-by-span with an underslung truss.
The last footing pour is expected to take place in early 2000, and construction of the bridge deck will begin in April. The estimated total volume of concrete in the bridge and ramps is 166,000 cubic yards (127,000 m3). VDOT is planning to open the highway by April 2002.
Owner: Virginia Department of Transportation
Developer/design builder: FD/MK LLC, Richmond, Va.
General contractors: Recchi America, Inc., Richmond, Va. McClean Contracting, J.V., Glen Burnie, Md. W. C. English Inc., Lynchburg, Va.
Ready-mix contractors: Tidewater Materials, Richmond, Va. Tarmac America, Inc., Richmond, Va.
Concrete pumper: Hydracrete Pumping Ltd., Richmond, Va.
Equipment: Putzmeister 42X- and 36-Meter pumps, Telebelt TB 105