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.