The Ministry of Transportation of Ontario (MTO) is considering alternative approach slab configurations to reduce the frequency and severity of pavement surface distress that are commonly observed at the end of approach slabs of bridges with integral abutments.
The MTO uses a standard approach slab that comprises a 6 m-long RC slab set near road grade and surfaced with 90 mm of asphalt. This slab configuration has performed satisfactorily for up to 10 mm of abutment displacement. However, asphalt cracking and settlements are observed at the far end of the approach slabs for displacements greater than 10 mm.
This paper presents the results of a study to find alternative approach slab configurations that can accommodate up to 25 mm of abutment/slab displacement and reduce the maintenance cost of IAB in Ontario.
As an alternative to the standard approach slab, the MTO is considering a number of approach slab designs ranging from angled slabs to buried slabs, with or without sleeper slabs, and potentially combined with soil or asphalt reinforcement, to reduce the effect of the underlying ground settlement on the transition from the approach slab to the bridge deck.
FEA was used to analyze the failure mechanism and the strain demands on the asphalt pavement. Different configurations of the slab were considered: slab inclination, slab depth below road grade, backfill reinforcement, installation of a buried sleeper, asphalt thickness and asphalt reinforcement. Based on these, the proposed slab configuration includes a 250 mm-thick asphalt reinforced with 3 layers of GlasGrid plus a 200 mm-depth, 1V:20H inclined approach slab supported on a buried sleeper at the far end of the approach slab.
The analysis showed that the proposed slab configuration can reduce in 70% the strain demands in the asphalt, in comparison with the current MTO slab configuration, and prevent cracking and settlements at the far end of the approach slab for 25 mm of displacement.