Lesson 6/Learning Event 4
gregate gradation after all aggregates and mineral filler entering the plant are blended together.
Selecting bin separations. The number of fractions into which the aggregate is to be
separated I established by specifications and depends primarily on the maximum size aggregate
to be used. With the C060 gradation unit, it is possible to separate the aggregate into three or
four size ranges. In this example, a four-bin separation will be used.
It is necessary to consider the plant bin arrangement and the size of the screen for the
fines bin to establish the best set-up for the most practical and efficient plant operation.
In most cases, it is desirable to separate the aggregate into the bins in proportion to the
bin storage capacities. To do this, it is necessary to know the gradation unit storage capacities.
They are:
Bin #1
14.2 tons
46%
Bin #2
5.8 tons
19%
Bin #3
4.3 tons
14%
Bin #4
6.5 tons
21%
Gradation Unit
30.8 tons
100%
(total capacity)
With the screens available, the smallest particle size that can be separated by the screening unit is
the #8 material.
NOTE: In many cases a separation at the #4 or #6 particle size instead of the #8 would be
desirable, practicable, and satisfactory. The #6 material is used as the separation in this
example to illustrate this point.
Referring to the gradation chart (Figure 20), the vertical line for the #6 material size
intersects the curve between two horizontal lines indicating that 47% of the aggregate is #6 and
smaller.
NOTE: Should specifications require the addition of mineral filler by the fines feeder the
percent specified is subtracted from the percent determined for Bin #1 from the aggregate
gradation chart.
Example: 5% mineral filler to be added by fines feeder.
47% of aggregate is #6 or smaller (Figure 20).
47% - 5% = 42% of aggregate is actually entering Bin #1.
Placing the first separation at the #6 material leaves a balance of 53% to be separated into three
size ranges.
Bin #2 has a capacity of 19%. Referring to the gradati6n curve (Figure 20) proceed from
the #6 material line. Count up on the #6 material line 19% (each line represents 2%) and then
read to the left to where the curve intersects the percentage line. The point of intersection lies
between the 1/4-inch and the 3/8-inch vertical lines. By interpolating to the 5/16-inch
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