526 Approach Slabs

Description (526.01)

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.


Materials (526.02)

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.


Setting Grades

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:

  1. Placing the deck and the approach slab together would not allow the installation of the Type A Waterproofing per Bridge Standard Drawing AS-1-81.
  2. Adjacent spans with large deflections, over 1 inch, could cause the semi-integral or integral abutment diaphragm to rotate on the bearing, which could cause the D800 bar in the continuously placed approach slab to move and damage the approach slab where the concrete's initial set had already began. Therefore, concrete placement sequences may be required, such as starting at the rear abutment, placing concrete in the bridge deck and continuing across the forward approach slab, then coming back and placing concrete in the rear approach slab.
  3.  Approach slab concrete cannot be placed with bridge deck concrete if semi-integral or integral abutment diaphragm concrete placement for steel members or prestressed concrete members is not done prior to concrete deck placement.
  4. Permit the placement of the approach slab with the bridge deck for integral or semi-integral designs if:
    1. The skew is less than 10 degrees for prestressed concrete beams.
    2. The skew is less than 30 degrees for steel beams.
    3. The deflection due to dead load of the adjacent span is less than 1 inch.
    4. There is no phased construction that requires the deck and abutment diaphragm to be placed together.
    5. The 1/2-inch joint for the preformed elastomeric compression joint seal between the deck and the approach slab is sawed as soon as possible for stress relief.

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. 


Documentation Requirements - 526 Approach Slabs

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.