Update provided on Keystone Bridge
By Willis Patenaude, Times-Register
The Keystone Bridge project continues to be a topic of conversation at Elkader City Council meetings. Project engineer Nate Miller from Origin Design was recently on hand to deliver the latest update. With the cracked stone repaired and the majority of the temporary shoring and berm removed, he started the meeting by stating, “It’s good to be back.” In the aftermath of the array of delays that slowed progress on the project over the past several months, everything is “starting to look downhill now,” he added.
The optimism stems from the progress made on non-critical path items that could still be completed when major parts of the project were put on hold due to the now-repaired cracked stone.
One of those items was filling voids throughout the bridge with grout. To date, Miller estimates that effort has injected approximately 24 cubic yards of mortar, which equates to being about three quarters of the way done.
Another item that was worked on during the overall shutdown was tuck-pointing, which includes the removal and replacement of deteriorated mortar between the stones throughout the bridge.
According to Miller, the importance of tuck-pointing is due to the fact the mortar “provides the load transfer between the individual limestone blocks in the structure.” In total, the tuck-pointing effort is currently halfway completed, and even as the contractor focused efforts on stabilizing the crack, Miller said this part of the project is “ahead of schedule.”
The issue of tuck-pointing led council member Deb Schmidt to inquire about the effort, and whether the contractor was going “above and beyond” to ensure minimal problems in the future. In his response, Miller indicated the condition of the tuck-pointing was worse in some places on the bridge than previously anticipated, but the issue is being “repaired correctly now” because the “right people are doing the work.”
That work is pumping a tremendous amount of grout into the Keystone Bridge, and even though this effort was reliant on representative samples and testing on the existing grout, a practice that missed the condition of the cracked stone, Miller remained confident the analysis of the mortar would not lead to a similar issue down the road. His confidence rests on the fact that the engineering sub-consultant was on site taking those samples and a “comprehensive mortar analysis was completed to select the appropriate material used in the repair.”
Another element of the update revolved around tie rods, which provide the anchorage of the cantilevered sidewalk to the bridge structure. According to Miller, the existing tie rods, which were installed in 1975 and were originally one inch in diameter, corroded over time, to the point that some were no bigger than half an inch.
“The hidden corrosion of the existing tie rods helps illustrate the importance of this restoration project,” Miller said.
The new tie rods, which will run through the full length of the bridge, will be made from a high strength steel while being wrapped in a protective sheath and encased in concrete to mitigate future corrosion issues. The ongoing work that’s been completed thus far had Miller confidently stating that the “bridge is solid.”
However, there was a concern raised by the council about the project: the structural integrity of the concrete being poured in cold weather conditions. On this issue, Miller explained there are a series of steps required when placing concrete during cold weather, such as preheating the area prior to pouring the concrete, insulating the concrete form work and monitoring temperatures during and after the pour to ensure the material has the ability to properly cure prior to freezing. Miller ensured council members the monitoring effort was being done correctly, and stated in a separate interview that there are no concerns over the structural integrity of the concrete or the longevity of it, despite the fact it was poured in colder temperatures. As Miller stated, “proper precautions were taken.”
The other question asked by the council was about the timeline. Peggy Lane and Randy Henning both inquired about how much remains and when the project is likely to continue in full capacity in the spring. According to Miller, the resumption of construction activities is wholly dependent on the weather, though, if given the opportunity, the contractor would “like to get started as soon as possible.” That would be March at the earliest, assuming the weather cooperates. Otherwise, construction activities won’t resume until April as currently scheduled. Completion is still set for late December of this year.
As for what remains, the list has 53 specific work items that need to be completed, including ongoing masonry restoration efforts, installation of the tie rods, sidewalk framing and pouring the elevated sidewalk, installation of a waterproofing membrane, subgrade preparation and bridge deck paving, additional sidewalk construction, installation of pavement marking and the installation of the ornamental railing.
As the update came to an end, Miller thanked the council and city for its patience and understanding, while adding that this restoration is a “once-in-a-generational type effort” and the removal of the six stones is a “signature project.”
Miller expanded on this statement in the interview, noting the uniqueness of the Keystone Bridge project and the history of the bridge itself, being the longest, double arch, stone bridge west of the Mississippi. Limestone arch bridges are simply disappearing from the country’s landscape, making this structure, which was built in 1889, historically important. Miller believes that importance is “hard to overstate.”
“This structure serves as the keystone of the historic downtown area, providing a physical connection from the downtown area to the courthouse and other sites east of the Turkey River. The bridge is also a crucial component to the character of the district, providing residents and visitors a powerful reminder of the city’s past. We applaud the city’s commitment to preserving this structure,” Miller said.
