TM 5-809-12/AFM 88-3, Chap. 15
the intended purpose of the base course. In general,
high level at these points, and objectionable material
the base course material should be well-graded high-
is prevented from infiltrating the cracks; and (d)
stability material. TM 5-822-6/AFM 88-7, Chap. 1
differential settlement due to nonuniform support or
and TM 5-818-2/AFM 88-6, Chap. 4 provide
frost heave is reduced materially. Guidance relative
requirements for base courses for additional support
to the use of reinforced pavement is discussed in the
and frost action. If the base course is for drainage,
following paragraphs.
a. Subgrade conditions. Reinforcement may be
the maximum particle size shall be 1-1/2 inches, and
no particles shall be smaller than the No. 4 sieve
used to control cracking in rigid pavements found
size. If a free-draining, open-graded subbase is used,
on subgrades where differential vertical movement
a filter layer may be placed under the base course to
is a definite potential (for example, foundations with
prevent pumping action and subgrade intrusion.
definite or borderline frost susceptibility that cannot
Coarse aggregate shall have a percentage of wear by
feasibly be made to conform to conventional frost
the Los Angeles abrasion test of not more than 50.
design requirements.)
b. Economic considerations. For the general case,
Uniform high-quality materials shall be used.
Weakly cemented rocks and most shales should not
reinforced rigid pavements will not be economically
be used; an exception would be baked shales
competitive with nonreinforced rigid pavements of
occurring adjacent to intrusive dikes. The frost
equal load-carrying capacity, even though a reduc-
susceptibility criterion listed previously in chapter 4
tion in pavement thickness is possible. Alternate
is also applicable to base course materials.
bids, however, should be invited if reasonable doubt
Durability will be checked if the base aggregate will
exists on this point.
c. Nonreinforced slabs. In otherwise nonrein-
be exposed to frost. Aggregates that break down
excessively when subjected to freeze-thaw cycles
forced floor slabs, steel reinforcement should be
will not be used.
used for the conditions below.
(1) Odd-shaped slabs. Odd-shaped slabs
5-5. Steel reinforcement.
should be reinforced using a minimum of 0.06
percent of steel in directions normal to each other
Under certain conditions, concrete pavement slabs
over the entire area of the slab. An odd-shaped slab
may be reinforced with welded wire fabric or de-
is considered to be one in which the longer
formed bar mats arranged in a square or rectangular
dimension exceeds the shorter dimension by more
grid. The advantages in using steel reinforcement
than 25 percent or a slab which essentially is neither
include: (a) a reduction in the required slab
square nor rectangular. Figure 5-3 presents an
thickness usually is permissible; (b) wider spacing
example of reinforcement required in odd-shaped
between transverse contraction joints may be used;
slabs.
(c) the width of crack opening is controlled, with
the result that load transmission is maintained at a
5-6
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