The Making of a Modern Marvel
The Making of a Modern MarvelPutzmeister trailer pumps and placing booms overcome obstacles on Colorado River Bridge project
STURTEVANT, WI (October 22, 2009) – As was done 76 years ago, the Hoover Dam is again making its mark in history books. Crews are conquering an engineering feat of constructing the most technically challenging bridge ever to be built in North America, the Colorado River Bridge. To help place concrete for this one-of-a-kind project, two Putzmeister placing booms and BSA trailer pumps are taking on the obstacles presented by the Hoover Dam surroundings.
The bridge is part of the Hoover Dam Bypass project, will hover around 900 feet (274m) above the Colorado River and run parallel to the dam. The bridge, with two lanes in each direction, is being built in an effort to alleviate traffic on U.S. Highway 93, which currently crosses the Hoover Dam to pass over the Colorado River.
Because the highway is the major commercial corridor between Arizona, Nevada and Utah as well as on the North American Free Trade Agreement (NAFTA) route between Mexico and Canada, the traffic congestion (an average of 14,000 vehicles a day) caused by the existing highway across the dam, imposes a serious economic burden to the country.
In addition, the traffic volumes, combined with the sharp curves of the highway near the Hoover Dam, create a potentially dangerous situation for Hoover Dam visitors and dam facilities. Once the Colorado River Bridge is complete, no through or truck traffic will be allowed on the existing roadway; only Hoover Dam visitors will be permitted.
Obayashi/PSM JV, a joint venture of Obayashi Corporation and PSM Construction USA, Inc., the general contractor, began construction on the 1,900-foot (579m) long open spandrel deck arch bridge in early 2005. The completed 1,060-foot (323m) spans of the twin concrete arches are the longest in North America, fourth longest in the world, and reach about 900 feet (274m) high at the apex.
Choosing the Right System
Obayashi/PSM JV had its work cut out for them; the project included the pre-casting and erection of pier columns up to 300 feet (91m) tall; construction of the twin, cast-in-place segmental concrete arch spans; and the installation of temporary twin cable stays that have a 2,500-foot (762m) span and are 330 feet (101m) tall to support the arches during construction.
“We called Putzmeister right away to discuss the project and what our possible concrete placing solutions for this complicated project would be,” says Wes Pollnow, construction manager of Obayashi/PSM JV. “We needed to know which solution would make the most sense and which would be most efficient; they have a true complete systems approach, helping us from the beginning of the project.
“The placing system they chose to maximize their concrete placement for the arch was MX 32/36Z and MX 36/38Z placing booms and BSA 2107 HP-E and BSA 2109 H-E trailer pumps.”
Overcoming the Extreme
To date, Obayashi/PSM JV has pumped and placed about 10,000 cubic yards (7,646m3) of concrete for the Colorado River Bridge.
Jeff St. John, project manager of Obayashi/PSM JV, says the pump manufacturer helped their team determine how and where to mount the placing booms and position the trailer pumps for all portions of the project.
“For construction of the twin arches, we positioned one trailer pump near the base of the Nevada arches and one on top of the arch footing in Arizona,” comments St. John. “A placing boom was also positioned on each the Nevada and Arizona side of the twin arches.”
The separate placing booms and their pedestals were flown via crane to each of the twin arches for mounting on their specially-designed platforms.
Once the placing booms and trailer pumps were in position, they were ready to step up to overcome the 100-plus degree weather, while pumping and placing the notorious, harsh Nevada concrete mix up 280 feet (85m) and out 530 feet (162m),
“All of the concrete mixes used for the arch were advanced concrete mix designs using harsh aggregates,” says St. John. “Liquid nitrogen has been used extensively for pre-cooling of the concrete in order to reduce the temperature the concrete reaches during curing.”
For the arches, a high-strength 10,000-psi concrete mix was used, and for the columns and pier caps a high-strength 6,000-psi mix was used.
Early in the project the concrete mixes were provided by Casino Ready Mix and Silver State Materials (now a part of the CalPortland Company), however in late 2007 Obayashi/PSM JV began operating their own concrete batch plant for the arch and deck concrete, and will continue to make their own until the project is complete.
“Even with the combination of the heat and the harsh mix, the trailer pumps were able to easily maintain a continuous concrete flow, at a timely pace, up to the placing booms so it would not clog the pipe system in the extreme conditions,” comments Pollnow. “In addition, the S-valves on the pumps had no problem gulping down the tough concrete mixes.”
The trailer pumps are able to provide a smooth, more controllable output of concrete because of each pump’s free flow hydraulic technology. Both pumps have a fully adjustable volume control to allow very slow pumping while retaining full concrete pressure.
The pumps have been outputting around 16 cubic yards per hour (12m3/hr) due to the job site’s extraordinary environment conditions. In order to avoid the intense heat and avoid traffic congestion, most of the concrete placements occurred at night.
“The pumps really provided that extra muscle we needed to push the concrete up and out to its final destination, and in fact, both trailer pumps have the capability to pump concrete up to 800 feet (244m) high.
“Also, the capabilities of the placing booms helped immensely to reach the exact point of concrete placement for each segment of the twin arches. Again, because of the unconventional setup, we really needed dependable booms, and they did not disappoint.”
Quinn Concrete Pumping, Inc. (Quinn) of Las Vegas has also lent its services to the Colorado River Bridge project. Quinn has supplied both pump operators and has provided their own Putzmeister equipment.
“Quinn was on site quite early on in the project for the footing and arch foundation concrete,” notes St. John. “They are a great team to work with, very dependable. We expect they’ll also be involved with placing the deck concrete as well.”
Most notably, Quinn’s 42X- and 58-Meter truck-mounted concrete boom pumps were on site back in 2005 to pump and place concrete for the Colorado River Bridge’s pier. The pier provides foundation for the vertical columns needed to support the arch of the bridge.
“The 58-Meter boom pump was positioned atop a cliff’s edge on site, and used its full boom length to place concrete into the hopper of the 42X-Meter which was situated in a gorge below on another cliff,” says Pollnow. “The 42X then stretched its boom to pump and place the concrete to its final destination. The equipment setup and performance was truly remarkable.”
To-date, Quinn has placed about 5,000 cubic yards (3,823m3) for the Colorado River Bridge project.
As of October 2009, about 80 percent of the bridge was complete. The remaining work on the project includes erecting the precast spandrel columns, installing tub girders, casting the pier caps, the deck, then the barrier walls and approach slabs.
Concrete placement is anticipated to be complete during summer 2010, with the bridge opening for public use in late 2010.