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Thursday, October 3, 2013

PennDOT answers questions about bridge preservation work on I-180

PennDOT answers questions about bridge preservation work on I-180

PennDOT has been getting recurring questions about the bridge preservation work taking place along Interstate 180 at Montoursville. District Bridge Engineer Lloyd Ayres, P.E., has gathered the most common questions and provides answers to share with all. Here they are.

1) Why are they always working on the bridge over I-180 at Warrensville Road?

The Interstate 180 bridges over Loyalsock Creek at Montoursville have had three projects performed since 1998. Each of these projects addressed routine bridge maintenance for different elements of the bridge. In layman’s terms; a bridge, just like a car, requires routine maintenance and preventive maintenance to be performed on various cycles depending on the part being maintained. If the routine maintenance or preventive maintenance is not performed, the bridge or parts of the bridge will have a shorter life span and require replacement. For example, the project performed in 1998 replaced the expansion dams of the bridge. 

The expansion dams are located at the ends of spans and allow the bridge to expand and contract due to temperature changes or allow the ends of the spans to rotate when the bridge deflects due to heavy loading. The expansion dam consists of steel armoring and a rubber seal. The steel armoring and rubber seal wear over time and must be replaced. The steal armoring is expected to last for 50 years while the rubber seal is expected to last 15 to 20 years. We do try to minimize the number of projects that are done to a bridge by performing several maintenance items under one contract, however, this is not always possible due to the maintenance cycle times and funding limitations.

The preservation project that is currently under construction is a project to remove the concrete roadway approach slabs, patch the concrete deck, replace the rubber expansion seals, and to place an epoxy deck overlay. Since we are removing the concrete approach slabs and replacing them with blacktop pavement, no future bridge maintenance will be needed for this item. The concrete deck patching and epoxy deck overlay are preventive maintenance items that will allow the concrete deck to have a longer service life. Essentially, the epoxy deck overlay acts similar to the shingles on the roof on your house. It prevents water and salt from entering into the concrete deck which would lead to the concrete deck deteriorating at a faster rate. 

The epoxy deck overlay is expected to last for 20 years. If we did not place the epoxy deck overlay now, we would most likely need to replace the concrete deck within the next 20 years. As stated above, the rubber expansion seal has an expected life of 15 to 20 years, and these are being replaced as part of the routine maintenance cycle.
Once this project is completed, we do not anticipate working on this bridge for another 15 to 20 years. At that time, we will need to replace the rubber expansion seals again and possibly place another epoxy deck overlay.

2) Why don’t they end before rush-hour traffic?
The current project was done in two stages to minimize the impacts to traffic during the Little League World Series. The first stage, which was done prior to the Little League World Series, consisted of removing the concrete approach slabs and patching the concrete deck. These items of work required concrete barrier to be placed and limited traffic to one lane across the bridge. Since this work required barrier, it was not feasible to open up both lanes of traffic until the items of work were completed. At the end of the first stage, both lanes of traffic were opened up for the Little League World Series.
The second stage of the project is now occurring. This stage consists of placing the epoxy deck overlay and replacing the rubber expansion seals. Traffic is again limited to one lane across the bridge to place the epoxy deck overlay. The epoxy deck overlay does require the deck to be clean before it is applied and also needs time to cure before we can place traffic on the overlay. Thus, that is why both lanes of traffic cannot be opened up during rush hour.

3) It seems that they never have to do anything with the green truss (steel) bridge at Montoursville; yet build projects with concrete rather than steel.
The Montoursville truss has had two projects since 1993. The steel truss was rehabilitated, painted, and a new concrete deck placed in 1993. Since all of the routine maintenance items were address with this major rehabilitation, we have had a longer period of time between projects. However, a project will be performed on this bridge within the next 10 years (sooner if funding becomes available) to place an epoxy deck overlay, paint the truss, and to replace the rubber expansion seals.

Every bridge has routine maintenance cycles and the time period between projects is dependent on the maintenance cycles and funding availability. Preservation projects go a long way in extending the service life of bridges that are in good condition to start with.

The current bridge preservation work on I-180 at Montoursville is expected to be wrapped up early next week.

1 comment:

Anonymous said...

People need patience and plan for delays. Road repairs seem to be a thankless job to those involved.