TM 5-822-5/AFM 88-7, Chap. 1
prevent excessive separation during concrete
13-3. Limitations.
placement. When the reinforcement is installed and
The design criteria for reinforced concrete pave-
concrete is to be placed through the mat or fabric,
ment for military roads and streets are subject to the
the minimum clear spacing between bars or wires
following limitations.
will be 1 times the maximum size of aggregate. If
a. No reduction in the required thickness of plain
the strike-off method is used to place the
concrete pavement should be allowed for per-
reinforcement (layer of concrete placed and struck
centages of longitudinal steel less than 0.05 percent.
off at the desired depth, the reinforcement placed on
b. No further reduction in the required thickness
the plastic concrete, and the remaining concrete
of plain concrete pavement should be allowed over
placed on top of the reinforcement), the minimum
that indicated in figure 13-2 for 0.5 percent
spacing of wires or bars will not be less than the
longitudinal steel, regardless of the percentage of
maximum size of aggregate. Maximum bar or wire
steel used.
spacing or slab thickness shall not exceed 12 inches.
c. The maximum length L of reinforced concrete
The bar mat or wire fabric will be securely anchored
pavement slabs should not exceed 75 feet regardless
to prevent forward creep of the steel mats during
of the percentage of longitudinal steel, yield
concrete placement and finishing operations. The
strength of the steel, or thickness of the pavement.
reinforcement shall be fabricated and placed in such
When long slabs are used, special consideration
a manner that the spacing between the longitudinal
must be given to joint design and sealant require-
wire or bar and the longitudinal joint, or between
ments.
the transverse wire or bar and the transverse joint,
d. The minimum thickness of reinforced concrete
will not exceed 3 inches or one-half of the wire or
pavements should be 6 inches, except that the
bar spacing in the fabric or mat. The wires or bars
minimum thickness for driveways will be 5 inches
will be lapped as follows.
and the minimum thickness for reinforced overlays
(1) Deformed steel bars will be overlapped
over rigid pavements will be 4 inches.
for a distance of at least 24 bar diameters measured
from the tip of one bar to the tip of the other bar.
13-4. Reinforcing Steel.
The lapped bars will be wired or otherwise securely
a. Type of reinforcing steel. The reinforcing
fastened to prevent separation during concrete
steel may be either deformed bars or welded wire
placement.
fabric. Deformed bars should conform to the
(2) Wire fabric will be overlapped for a dis-
requirements of ASTM A 615, A 616, or A 617. In
tance equal to at least one spacing of the wire in the
general, grade 60 deformed bars should be
fabric or 32 wire diameters, whichever is greater.
specified, but other grades may be used if
The length of lap is measured from the tip of one
warranted. Fabricated steel bar mats should
wire to the tip of the other wire normal to the lap.
conform to ASTM A 184. Cold drawn wire for
The wires in the lap will be wired or otherwise
fabric reinforcement should conform to the
securely fastened to prevent separation during
requirements of ASTM A 82, and welded steel wire
concrete placement.
fabric to ASTM A 185. The use of epoxy coated
steel may be considered in areas where corrosion of
13-5. Design Examples.
the steel may be a problem.
As an example, let it be required to design a rein-
b. Placement of reinforcing steel. The
forced concrete pavement for the same set of con-
reinforcing steel will be placed at a depth of hd +
ditions used in the initial design example given
1 inch from the surface of the reinforced slab. This
previously in paragraph 12-4. Using Tthevalue of hd
will place the steel above the neutral axis of the slab
of 7.9 inches, the percentage of longitudinal re-
and will allow clearance for dowel bars. The wire or
inforcing steel S required to reduce the pavement
bar sizes and spacing should be selected to give, as
thickness to 7 inches is obtained from figure 13-2 as
nearly as possible, the required percentage of steel
0.10 percent. Similarly, the percentage of longi-
per foot of pavement width or length. In no case
tudinal reinforcing steel required to reduce the
should the percent steel used be less than that
pavement thickness to 6 inches is 0.30 percent. The
required by figure 13-2. Two layers of wire fabric
percentage of transverse reinforcing steel would be
or bar mat, one placed directly on top of the other,
either 0.05 for a design thickness of 7 inches or
may be used to obtain the required percent of steel;
0.15 for a design thickness of 6 inches. The choice
however, this should only be done when it is
of which percentage of steel reinforcement to use
impracticable to provide the required steel in one
should be based on economic considerations as well
layer. If two layers of steel are used, the layers must
as on foundation and climatic conditions peculiar to
be fastened together (either wired or clipped) to
13-5
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