TM 5-822-7/AFM 88-6, Chap. 8
"D" line cracking in pavements has been a problem,
gravel is used. When mixture proportioning studies
limestone aggregates should not exceed -inch
or local experience indicates that a low flexural
nominal maximum size and should be of low absorp-
strength will be obtained with uncrushed gravel, the
tion. When the nominal maximum size of coarse
possibility of obtaining higher strength by crushing
aggregate is greater than 1 inch, the aggregates
the gravel will be investigated. Elongated particles
shall be furnished in two size groups as shown in
with a widthto-thickness ratio in excess of 3 may
table 2, with gradings within the separated size
not exceed 20 percent by weight as determined by
groups conforming to the requirements of table 3.
CRD-C 119. This requirement attempts to avoid
Where local practice provides size-group separations
introducing structural planes of weakness in the
other than as shown in table 2, local size gradings
finished concrete, workability problems associated
may be specified if approximately the same size
with an excess of particles of these shapes, and
ranges are obtained and the grading of coarse aggre-
durability problems that may develop if air and
gate when combined and batched for concrete is as
water are trapped under flat and elongated particles.
required by mixture proportioning. For projects
(2.) Size and grading. The maximum size of the
requiring 1,600 cubic yards or less of concrete,
coarse aggregate used in pavement concrete should
special grading requirements for coarse aggregate
not exceed one-fourth of the pavement thickness. In
according to local practice may be substituted for
no case will the coarse aggregate exceed a 2-inch
the gradings shown. Local State Department of
maximum size. However, for pavement construction
Transportation specifications for gradings may be
in areas where aggregate popouts have been a problem
or may occur, the coarse aggregate will not exceed
used for those jobs requiring 1,600 cubic yards or
1-inch nominal maximum size. In areas where
less of concrete.
Table 2. Coarse aggregate size groups
L
Size Groups
Nominal Maximum Size
No. 4 to in.
1 in.
in. to 1 in.
No. 4 to 1 in.
2 in.
1 in. to 2 in.
5
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