14-hour concrete pour prepares first lengthwise 'half' of new Cimarron/I-25 bridge
The work was accomplished by close to 100 workers with Kraemer North America - the contractor for the $113-million interchange replacement project by the Colorado Department of Transportation (CDOT) - in a non-stop endeavor between 3 p.m. Sept. 13 and 5 a.m. Sept. 14.
Because of the possibility of concrete dripping down, Cimarron Street (below the bridge) was closed for the night in both directions, once the pour got near to actually being over the roadway itself.
According to Don Garcia, deputy project manager with CDOT consultant Wilson & Company, the area of concentration covered a bridge area 359 feet in length and 80 feet in width, with the concrete needing to be leveled at 9½ inches high.
In all, the project required 760 yards of concrete. Putting that in perspective, a single concrete truck mixer holds a load of 7 yards, Garcia noted. So the pour needed more than 100 mixer loads.
During the work, the trucks could be seen lined up on a closed-off area below and to the west side of the bridge, where a machine attached to each truck in turn pumped its load upward through a line arching over and down to the bridge deck. The overall concrete travel distance was 183 feet, Garcia said.
The pour used the Bidwell system, which, according to the Terex Bid-well website, was developed by South Dakota bridge contractor “Tex” Bidwell in 1961 and has since become the industry standard. As seen in photos with this article, a Bidwell consists of metal units bolted together as needed to match the width of a bridge. One type of Bidwell unit, called a “screed,” has an operator standing on top controlling mechanical equipment which handles the lion's share of the concrete-leveling chore.
During the Sept. 13-14 Cimarron/I-25 pour, the pumped concrete came out of a wide hose, whose steady flow was directed by a worker slogging at times through the concrete itself near the Bidwell. Slogging with him - and like him wearing high rubber boots for the purpose - were numerous fellow workers, who helped to distribute the liquid mass as evenly as possible to the 9 ½-inch height before it solidified. They were using shovels, hand-held leveling devices and vibrating tools that “assure the proper consolidation of the concrete around the rebar,” Garcia explained.
At 80 feet, the now-concreted bridge represents just over half of the planned, final interstate width over Cimarron. The rest of it, to be completed in 2017, will add 71 feet to the width, making it a total of 151 feet across. The 80-foot side has been called the "southbound" bridge (for ease of explanation), because at project's end it will carry the southbound lanes (and a little bit more). However, when engineers discuss the construction as a whole, they say that the coming 71 feet will be "added" to the 80 feet, meaning that technically the southbound and northbound sides will all be one big bridge.
Roadwork is still needed on a short stretch south of the bridge to link up with a new I-25 segment that was realigned between Cimarron and the Nevada/Tejon interchange this summer.
What will happen in October (date not yet specified) is that the 80-foot bridge portion and the southbound side to Nevada will start temporarily carrying both southbound and northbound traffic. It will be a tight three lanes each way, with narrower lanes and shoulders, but as Garcia explained, the project had to be done this way because the bridge couldn't be built any wider while the old northbound bridge at Cimarron was still handling traffic. That bridge can now be taken down. The demolition will happen later this year, the schedule shows. Built in its place, sometime in 2017 will be the new bridge's other "half."
Mark Bilby, a structural engineer with WSP Parsons Brinckerhoff, Inc., is quoted in a CDOT press release about the unique lengthwise stability of the new bridge. "There aren't many bridges in Colorado like the new I-25 bridge at the Cimarron Street/US 24 exit," Bilby said. "It's a highly efficient bridge for the size of girder being used, [with] three girder segments of varying lengths, that when spliced together with post-tensioned cables, creates an efficient two-span bridge... The pre-stressing and post-tensioning processes maximize the length of the bridge span and eliminate the need for another pier, which would otherwise need to be constructed in the middle of Cimarron Street.”
Westside Pioneer article