d. A diagram shall be plotted using a rectangular scale with WF on the
Y-axis with units from 20 (bottom) to 45 (top), and with CF on the
X-axis with units from 80 (left side) to 30 (right side). On this
diagram a parallelogram shall be plotted with corners at the following
coordinates (CF-75, WF-28), (CF-75, WF-40), (CF-45, WF-32.5), and
(CF-45, WF-44.5. If the point determined by the intersection of the
computed CF and WF does not fall within the above parallelogram, the
grading of each size of aggregate used and the proportions selected
shall be changed as necessary.)
e. A blending aggregate shall be used to meet the required combined
grading. This blending aggregate shall be batched separately. The
combined grading of all aggregates used, in the proportions selected,
shall be computed on the basis of cumulative percent retained on each
sieve specified for fine and coarse aggregate.
2.2.2
Coarse Aggregate
2.2.2.1
Material Composition
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NOTE: Crushing gravel tends to improve quality and
bond characteristics and generally results in higher
flexural strength of concrete. When mixture
proportioning studies or local experience indicates
that low flexural strength concrete will be produced
with an uncrushed gravel, the possibility of
producing higher strength concrete by crushing the
gravel should be investigated. When desirable to
limit coarse aggregate to crushed materials, modify
this paragraph appropriately.
Do not, under any conditions, permit use of steel
furnace slag for any aggregate. (It is markedly
different from iron blast furnace slag.)
In power check pads, the high temperatures from jet
blast can cause distress in aggregates in the
concrete. Include bracketed item if power check
pads are to be constructed. If no service record is
available, lab study of available aggregates should
be made.
Special attention should be given to aggregates to
be used for compass calibration pads. Aggregates
with magnetic properties, such as, but not limited
to, magnetite in granites, high-iron minerals in
traprock, pyrite in limestone, and free iron or iron
oxide in slag aggregate should not be used. When
the paving of compass calibration pads is required,
add the bracketed item concerning compass pads as
additional requirements for coarse and fine
aggregates.
If reclaimed portland cement concrete is permitted,
retain the bracketed portion regarding reclaimed
PCC; otherwise, delete. If reclaimed PCC is
permitted to be used, laboratory studies must be
SECTION 02753
Page 37
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