used to handle bulk cement. Bulk cement is measured
in tons (2,000 lb) and smaller quantities are bagged in
cloth or paper sacks, each containing 94 pounds of
cement. A 94-pound sack of cement is equal to 1 cubic
foot by loose volume.
Cement bags should not be stored on damp floors,
but should rest on pallets. The bags should be stacked
against each other to prevent circulation of air between
them, but not stacked against outside walls. If the stacks
of cement are to be stored undisturbed for long periods,
they should be covered with tarpaulins.
Cement bags that have been stacked in storage for
long periods sometimes acquire a hardness called
WAREHOUSEPACK. This can usually be loosened by
rolling the sack around. Cement that has lumps or is not
free flowing should not be used.
separately-the fine aggregates on sieves with openings
1/4 inch or smaller and the coarse aggregate on sieves
with square openings from about 1/4 inch and larger.
The fine sieves are numberedthe larger the number, the
smaller the sieve opening; for instance, the No. 100
sieve has 100 openings per inch, and the No. 4 sieve has
4 openings per inch.
The grading of both coarse and fine aggregate and
the relative proportions of each in the mix can greatly
affect the properties of the fresh concrete. Concrete
made with coarse sand or not enough sand is hard to
pump and will be harsh and difficult to trowel. Also,
aggregates can segregate or separate from the cement
paste during placement, producing nonuniform
concrete. Air-entraining will help in overcoming
grading problems of this kind. Coarse aggregates should
be round or subround in shape. This thape allows the
cement paste to coat the particles more easily during
The aggregates used in concrete must be strong,
HANDLING AND STORAGE OF
durable, and chemically inert and generally occupy 60
to 75 percent of the concrete mix in volumc (70 to 85
percent by weight). Natural aggregate deposits are
Aggregates containing particles of different sizes
excavated from pits, rivers, lakes, or seabeds. These
have a natural tendency to segregate whenever loaded,
natural deposits consist of gravel and sand that can be
transported, or otherwise disturbed. Aggregates should
readily used in concrete after minimal processing.
always be handled and stored by a method that
Crushed aggregates are produced by crushing quary
rock, boulders, cobbles, or large-size gravel. Crushed
Stockpiles should not be built up in cone shapes,
aggregates are usually washed and graded before being
formed by dropping successive loads at the same spot.
used in concrete. The most commonly used aggregates
This process causes larger aggregate particles to
are sand and gravel and when combined with cement
produce a strong, durable mass that is practically
segregate and roll down the sides, leaving the pile with
a large amount of fine aggregate at the top and a large
amount of coarse aggregate at the bottom. A stockpile
The coarse aggregates used in a mix usually consist
should be built up in layers, each made by dumping
of gravel or crushed stone up to 1 1/2 inches in size.
successive loads alongside each other.
Course aggregates are primarily used as filler. These
If aggregate is dropped in a free fall from a
aggregates can pass through a 3-inch sieve and are
retained on a No. 4 sieve. In massive structures like
clamshell, loader, or a conveyor, some of the fine
dams, the coarse aggregates may include natural stones
material may be blown aside, causing segregation of
fines on the lee side of the pile. Clamshells, loaders, and
or rocks, ranging up to 6 inches or more in size.
conveyors should be discharged in contact with the
Fine aggregates are those materials that can pass
through a No. 4 sieve but are retained on a No. 100 sieve.
The fine aggregates and sand in concrete are used to fill
the voids between the large aggregates. Care should be
taken to prevent dirt and othcr debris from getting mixed
into the sand. The foreign material affects the bonding
quality of the sand.
The gradation of the aggregate is a major factor in
the workability, water requirements, and strength of
concrete. Fine and coarse aggregates are usually sieved
The bottom of an overhead charging bin should
always slope at least 50 degrees towards the center
outlet. If the slope is less than 50 degrees, segregation
will occur as the material is discharged. When a bin is
being charged, the material should be dropped from a
point directly over the outlet. Material dropped in at an
angle or discharged against the sides of the bin will
segregate. Since a long drop causes both segregation and
the breakage of aggregate particles, the length of a drop