“Heat reduction was the key factor in selecting the 70/30 slag cement and portland cement mix, but strength was an added bonus,” says Luther. Although the specification for the bridge piers required 6000 psi concrete, Riley’s slag mix achieved up to 8000 psi.
The producer made test cylinders from day one through day 56, even after the project was underway. “We kept the testing as consistent as possible, and the project partners all collaborated to ensure we got the mix right,” says Riley. As a result, the concrete consistently met and exceeded the project’s strength requirements, without a single failure. “MTA had great results with the slag mix, including reduced cracking,” says Hitt.
The low-cement mix also helped reduce the amount of materials on the project. As the foundation design was being completed, MTA recommended reducing the bridge footer thickness from 25 to 20 feet, based on the concrete’s design strength.
But there was room for improvement in the project’s early days. “MTA was having trouble pumping the slag mix as far as they needed it to go—about 300 feet,” says Riley. “After a couple of long nights, we knew we had to make an improvement.” Working with local aggregate suppliers, the producer added a special blended sand to resolve pumpability issues. With the slag mix perfected, the contractors used it for all of the mass concrete elements of the river piers.
Rising from the water
Riley designed a fly ash mix for the bridge towers, which are hollow to allow for maintenance access and installing the stay cables. “When we reached the point where heat of hydration wasn’t as much of a concern, we switched to a more conventional mix,” says Riley. Riley Illinois also produced high early-strength concrete for the bridge overhang and infill pours between precast deck panels.
The 13-by-43.5-foot precast panels, weighing about 70,000 pounds each, were fabricated in St. Peters, Mo., and delivered by XL Contracting. Each 45-foot section of the deck included two edge girders and three floor beams, with 10-inch-thick precast panels. “We preassembled the 230,000-pound structural steel sections for the bridge on barges to save time on the critical path,” says Tavernaro.
After lifting and installing each massive section with a crane, the contractor placed filler strips between the panels, mostly delivered by bucket and crane from the riverbanks. “We used a high early mix because the concrete had to achieve 3500 psi before we could do any post-tensioning,” says Tavernaro. A 2-inch, latex-modified concrete overlay for the deck was volumetrically batched onsite and installed by XL Contracting.
As work on the cantilevered deck progressed, it extended from each end at a rate of about 85 feet each month. The two sides met in the middle to complete the deck in August 2013.
Planning the next phase
Once traffic is flowing smoothly on the new bridge, MoDOT and IDOT will focus on improving the Poplar Street Bridge and ramps. The ramp connections to and from I-55 will be made two lanes wide and will have more gentle vertical grades and horizontal curves. The existing Poplar Street Bridge will be resurfaced and widened to add one more lane. The $91 million in additional work should be completed by mid-2017.
With the Stan Musial Veterans Memorial project under his belt, Riley plans to bid on future phases. “We had a good experience working with MoDOT and a very good team—and got through the project without any major problems or hiccups,” he says with pride.
For more information, visit www.newriverbridge.org. Visit the producers at www.rileyreadymix.com and www.kienstrareadymix.com.