The Iowa Department of Transportation has long recognized that approach slab pavements of integral abutment bridges are prone to settlement and cracking, which manifests itself as the "bump at the end of the bridge". The bump is not a significant safety problem; rather it is an expensive maintenance issue. A commonly recommended solution is to integrally attach the approach slab to the bridge abutment, which moves the expansion joint typically found at the approach slab/abutment interface to a location further from the bridge where soil settlement is less of a concern and maintenance is easier. For existing structures the typical maintenance activities, such as adding wedges of asphalt to reduce the bump, are temporary fixes and do not address the underlying problem until the only remaining alternative is replacement of the approach slab. Finding ways rapidly make repairs, and thus decreasing the effects on traffic is critical. One promising solution for reducing construction durations, which the Iowa Department of Transportation has been testing and evaluating, is the use of precast concrete pavement and bridge elements.

For this study, two different approach slabs, one being precast concrete and the other being cast-in-place concrete, were integrally connected to twin parallel bridges on Iowa Highway 60. The primary objectives of this investigation were to evaluate: the viability of precast approach slabs, the approach slab performance, and the impacts the approach slabs have on the bridge.

The Iowa State University Bridge Engineering Center installed a monitoring system on both bridges and the approach slab systems. Several behavior facets were studied and monitored during the evaluation period including abutment movement, bridge girder strain changes, approach slab strain changes, approach slab joint displacements, post-tensioning strain, and abutment pile strain changes. The project scope also involved a literature review, a survey of Midwest Department of Transportation current practices, onsite observation of the fabrication and installation of the precast approach slab panels, and periodic visual inspection of the bridges.

From the onsite observations and the year-long monitoring the following general conclusions were made: (1) the integral connection appears to function well with no observed distress or relative movement of the approach slab and bridge; (2) the approach slab to the bridge connection appears to impact the bridge to a minor degree; (3) the two different approach slabs appear to impact the bridge differently; (4) the measured strains in the approach slabs indicate a force exists at the expansion joint which should be taken into consideration during the design stage; (5) the observed responses generally followed an annual cycle with shorter term cyclic patterns; (6) metal forms should be used to ensure a quality precast product; (7) larger access pockets should be used; and (8) finer granular material would allow easier and more precise adjustments of the panels.