Longest Boom Boosts Production on Colorado’s Highest Bridge

The only concrete pump in North America with a 58-meter placing boom made distant deck pours that helped contractors complete construction of the highest bridge in Colorado. The 1,225-ft-long structure over Aregua Gulch is part of an expansion project at a gold mine site west of Colorado Springs in the Victor-Cripple Creek area.

State Highway 67 bisects the Cripple Creek & Victor Gold Mine in the Rocky Mountains, where the mine’s excavation area lies to the north of the highway and its leaching operations to the south. The leach pad is being expanded from 115 acres to 379 acres to accommodate increased volumes of crushed rock that are treated with sodium cyanide in the gold extraction process. Ames Construction Co., Denver, is building the relocated roadway and expanded leach pad.

Ames’ work and the bridge construction were started in November 2000, as bridge subcontractor Edward Kraemer & Sons alternated a series of Schwing concrete pumps to make footing and pier pours. Working at nearly 10,000 ft altitude in winter weather conditions, the truck-mounted pumps from Brundage-Bone Concrete Pumping, Denver, used booms sized at 28, 36, 42, 52 and 55 meters.

“The pumps completed the two 60-ft-high end-piers,” says Brundage Bone’s Keith Joiner. “We reached up l80 ft in 16-ft lifts with the Schwing 55 to start the two middle piers. These piers are 240 ft high and were topped off with Kraemer’s crane and bucket.”

The four hollow piers, formed at l4x7 ft, their footings and caps consumed 3,500 cu yds of concrete from Transit Ready Mix on a long trek from Colorado Springs. Hauls up to 2 hrs required a retarder in the mix, blockouts for propane heaters inside the hollow columns and insulation blankets inside and outside the forms. The long haul times resulted partly from the difficulty in navigating the steep canyon grade to reach the pumps that were positioned on dozer-cut benches in the slopes.

“At times the difficult access for mix trucks really slowed down production,” says Lee Jones, Kraemer’s senior project manager. “One access road had a 27 percent grade. We had to ease the mix trucks down and back up again with Cat D-10 dozers when the grade was wet and slippery.”

High steel and concrete

Additional obstacles confronted bridge crews when superstructure work was started by steel erection contractor Olsenbeal of Linden, Utah. Steel had to be similarly guided down the same steep slopes with dozer assistance to the cranes below. And high winds whistling through the canyon or dangerous lightening storms frequently halted crane picks of the 8-ft-deep plate girders that run up to 112 ft long. The deck required four strings of girders for each of its five spans. In all, 64 girder picks were made for the bridge, whose end spans are each 207 ft and three inner spans are 266 ft.

An additional l,600 cu yds of concrete went into the deck slab in a well conceived plan that ultimately completed the project in a tidy 11 months – at least 5 months earlier than a typical bridge job of this scope would require, according to Jones. “In this terrain and under these weather conditions, a bridge of this size would normally take close to a year and a half to complete,” says the veteran project manager.

“We couldn’t bucket the mix because our 310-ft crane boom could only swing half-way across the deck,” Jones recalls. “And while we considered conveyers, we were concerned with segregation and slump loss.”

Kraemer & Sons, headquartered at Plain, Wis., but working out of its Castle Rock, Colo., office, opted for a combination of Schwing concrete pumps, a Bidwell deck finishing machine and a Conform mini-placer (or spider) that teamed in an efficient place/finish operation. To speed concrete delivery, Transit Ready Mix avoided long hauls from Colorado Springs by setting up a portable batch plant on site last July. Pour No. l was started and completed by a Schwing 47-meter boom pump (the mini-placer was not used on the shorter end-span pours). Some 300 cu yds was placed and finished in 5 hrs.

Debut of the big 58

Working from north to south, deck paving was scheduled to complete one continuous pour each week for five weeks. Pour No. 2 saw the introduction of the first production model of the Schwing S 58 SX, a pump with the industry’s longest boom, and the only one working anywhere on the continent. Positioned on a bench on the slope, the 58 extended its 188-ft boom up and over the 60-ft-wide deck surface to feed the mini-placer that distributed the mix.

The mini-placer and finishing machine ride on rails spaced at 12 ft on chairs above the reinforcing steel for the 8-in.-thick deck slab. They are pulled by a pair of electric winches powered by a generator on board the spider, which is mounted on an I-beam frame with wheels. In operation, an average 250 ft of pipeline from the pump boom to the mini-placer was decreased in l0-ft sections as paving advanced.

With the spider placing the full 60-ft deck width on the three inner spans and the trailing Bidwell finishing the fresh concrete, Pours 2, 3 and 4 were completed with the concrete pump line avoiding any contact with the reinforcing steel – the only reason for using the mini-placer, according to Brundage-Bone’s Joiner. Pours 2 and 3 saw the new 58-meter Schwing pump teamed with the mini-placer.

The more accessible Pour No. 4 combined the mini-placer with a Schwing 36-meter, the only pump that worked from atop the deck. Pour No. 5, the south end-span, eliminated the spider, while teaming the big Schwing 55- and 58-meter pumps to pour the deck’s final yards.

The bridge’s five spans were completed in five separate pours that crossed over from the shorter end-spans to balance the concrete volume for each pour. Bulkheads were established every 245 ft between pours. About 300 cu yds was placed per pour in an average of five hrs — in often severe weather conditions and the rugged Rocky Mountain terrain.

On the steep slope of the gorge the new S 58 SX pump was comfortably positioned in its small footprint of only 29 ft. that maximizes the reach of the four-section boom. The pump’s X-front telescoping outriggers are curved to extend around obstructions, and the unit’s front- and rear-axle steering enabled the 58 to maneuver like a smaller pump in tight quarters at the bridge site.

At 250 ft above the floor of the Aregua Gulch, Colorado’s highest bridge saw the last yards of concrete poured in early September. Form stripping and cleanup followed, and Kraemer crews – that frequently worked l0-hour days for six, and even seven, days a week – finished building the $8 million span in an outstanding 11 months, meeting the project’s fast-track deadline.