Precast Prestressed Concrete Approach Slabs

The “bump at the end of the bridge,” which is caused by bridge approach slab settlement, is an ongoing problem for many state highway agencies. The bump not only degrades the ride quality of a roadway, but also presents a safety issue for drivers and increases impact loads on bridges. Approach slab settlement is generally caused by a loss of support due to consolidation or erosion of the underlying embankment material, and can be accompanied by failure of the supporting paving notch. While problems with the embankment material can be prevented with improved construction practices, a separate but equally important issue is how to reconstruct bridge approach slabs that have already failed. This is particularly challenging in urban areas where lane closures must be minimized to reduce the impact of reconstruction on the traveling public. The Iowa Department of Transportation and Federal Highway Administration are addressing this issue by investigating the use of precast prestressed concrete pavement (PPCP) for expedited bridge approach slab reconstruction. Precast panels are fabricated and stockpiled at a precast plant, then delivered to the jobsite and quickly installed as needed. Precast panels can support traffic immediately after installation, thereby facilitating overnight or weekend construction operations. Prestressing the approach slab benefits performance by keeping the pavement in compression to minimize or even eliminate cracking, while also giving it a “bridging” ability to span voids that may redevelop beneath it over time. Further, prestressing allows the expansion joints to be moved further away from the bridge abutment, reducing the probability of water infiltration into the underlying embankment near the abutment.