TM 5-809-6/AFM 88-3, Chap. 6
(d) Structural items like expansion plates, rocker
densely mixed overlay, or both will be provided to prevent
joints, and surfaces intended to permit movement will be
corrosion of reinforcing steel. Specific guidance should be
designed so they are protected against direct contact with
obtained from local or state highway department officials.
water or condensation and will be detailed to readily drain
Bridge decks subject to repeated applications of deicing salt
water.
will require more than additional concrete cover for
(e) Surfaces and members will be designed so water
reinforcing. Epoxy coated reinforcing bars and densely mixed
will drain from points where steel contacts or enters into
concrete overlays are considered the most effective methods
masonry or concrete.
and are approved by the Federal Highway Administration.
(2) Exposed conditions.
(d) Vertical expansion and contraction joints for
(a) Wherever possible, contact between masonry and
reinforced concrete retaining walls and similar structures will
wood or metal in exposed conditions will be prevented.
be spaced sufficiently close to reduce or eliminate wall
Usually, the best way to drain masonry is to put weep holes
cracking due to shrinkage and expansion.
(e) In coastal areas, continuous concrete or masonry
where they will not adversely affect member strength.
(b) Where exposed and uncoated steel structures are
foundation walls or grade beams will be extended 24 inches
used, an increased thickness of at least 1116 inch for
above grade for wood or steel exterior walls so the junction
corrosion allowance will be used over the computed
will be above the splash zone.
(3) Buried or semi-buried structures. Structures of this
thickness required. No corrosion allowance for corrosion-
resistant or weathering steel is required.
type will be designed to resist buoyant forces caused by the
(c) Exposed concrete structures will have enough
presence of water. The safety factor will be at least 1.5 at
protective concrete cover to protect the reinforcement. The
maximum water table using the dead weight of the structure
concrete mixture will be of maximum density and minimum
without contents plus the weight of earth cover directly over
shrinkage, especially with regard to longtune shrinkage and
the tank. A safety factor of 1.1 may be used when the
expansion which may be caused by alternate wetting and
maximum water table or the maximum flood level is at or
drying. For bridges or structures exposed to corrosive
above the top of the structure. Designers will consider the
chemicals or deicing salt, epoxy coated reinforcing bar, a
possible hydrostatic uplift at various stages of construction.
2-3
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