Figure 5-3.-Sieve sizes.
Limestone. Limestone is widely used
for road surfacing, in concrete, and for
l i m e .
Gneiss.
Most
varieties
of
gneiss
have good strength and durability and make
good road aggregates.
Quartzite.
Quartzite
is
both
hard
and durable. Because of these qualities,
it is an excellent rock for construction,
although it is often difficult to quarry.
Marble. The texture and color of
marble
make
it
very
desirable
for
dimension stone, and it can be used for
base course or aggregate material.
Sieve Analysis
Soil
is
composed
of
particles
of
various sizes and composition. Figure 5-2
shows the major types of soils. Soil can
be analyzed by size by sifting a dried and
weighed sample through a set of testing
sieves
(fig.
5-3)
and
weighing
the
material retained on each screen. Further
testing
may
be
required
by
the
specifications for the product you need to
produce.
These
tests
are
normally
performed by the soil laboratory in the
engineering department of the battalion.
Soil is classified according to the
particle size, such as coarse aggregate,
fine
aggregate,
and
mineral
filler.
The
maximum
size
of
the
aggregate
varies,
depending
upon
the
construction
specifications.
Particle
size
is
defined
by passing a soil mass through several
sieves with different sized openings (fig.
5-3).
Particles that pass through a given
sieve are said to be passing that sieve
size. Particles that fail to pass through
a given sieve are said to be retained on
that
sieve.
The
sieve
permits
particles
smaller than the opening to fall through
and retains the larger particles on the
sieve. When you use sieves with screen
openings of different sizes, the soil can
be separated into particle groups based on
size.
A weighted sample of aggregate is
placed in the top sieve, and the entire
set
of
sieves
(largest
on
the
top,
smallest on the bottom) is vibrated either
by hand or mechanically. The individual
weights are calculated as a percentage of
the
total
weight,
as
shown
in
the
following example: Assume we take 3,000
grams of soil mass and determine how much
aggregate passes each sieve.
Aggregate
passing
1/2-inch
sieve and retained on
3/8-inch sieve = 720 grams = 24%
Aggregate
passing
3/8-inch
sieve and retained on No. 4
sieve
=
600
grams
=
20%
Aggregate passing No. 4
sieve and retained on
No. 10 sieve = 450 grams = 15%
Aggregate passing No. 10
sieve and retained on
No. 40 sieve = 570 grams = 19%
Aggregate passing No. 40
sieve and retained on
No. 200 sieve = 420 grams = 14%
Aggregate
passing
No. 200 sieve = 240 grams = 8%
3,000 grams = 100%
The above percentages are one way of
expressing the gradation of a sample of
aggregate.
5-5