An approach slab is designed to function as a bridge deck spanning the distance from the bridge abutment to beginning of the roadway pavement. As a result, it is designed and constructed similar to a bridge deck.
The concrete used to construct the approach is the same class as the bridge deck and should be placed using the same specifications as the bridge deck concrete. If the project does not identify the class of concrete used for the superstructure, or if the deck is composed of prestressed box beams with an asphalt-wearing surface, Class QC-2 or Class S concrete, depending on the quantity required for the approach slab, should be used.
It is important that the approach slab be constructed parallel to the surface of the bridge deck to provide a smooth ride from the approach pavement to the bridge deck. To accommodate the actual dead load deflection of the deck, which may vary from the anticipated dead load deflection, the approach slabs should not be placed until after the deck has been placed. However, in an attempt to achieve a smoother ride, District Bridge Engineers have allowed Contractors to place the approach slabs continuously with the bridge decks, especially for some semi-integral and integral abutment designs. Some things to consider if the approach slabs are placed continuously with the bridge deck:
The final grade of the approach slab can then be established by using a string line. One end of the string line should be secured at a distance of approximately 10 feet (3 meters) back on the deck and stretched over the proposed approach slab with the other end attached to a grade stake marked with the proposed pavement grade. The final grade of the approach slab can then be determined.
The Contract plans will show the length of the approach slab. All other details are dictated by Standard Drawing AS-1-81. It will show the reinforcing and joint requirements as well as slab thickness and haunch details.
1. Length, width, and depth of forms.
2. Porous backfill exposed at abutment.
3. Number of bars and clearance maintained on reinforcing steel. Tied per 526.03.
4. Dowel bars, if used.
5. Surface finish.
6. Grooved longitudinally to match deck grooving.
7. Amount of curing compound used.
8. Measure length and width for pay.
Type A Waterproofing applied to the face of the deck, backwall, or beams as shown in Bridge Standard Drawing AS-1-81 prior to placing concrete for the approach slab.