CHAPTER 7
CONCRETE BATCH PLANT SUPERVISOR
Concrete is a mixture of cement and water that binds
aggregates, such as sand and gravel or crushed stone,
into a rockdikc mass and when properly constructed, it
is very rigid and has a long life. This is a result of the
chemical reaction between the cement and water called
hydration. The Naval Construction Force (NCF) has
various equipment used to provide concrete for
construction purposes. This equipment ranges from the
11S mixer, transit mixer, mobile concrete mixer plant
(crete mobile), and the concrete batch plant.
Most concrete production operations are supported
by an experienced Builder (BU). However, EOs must
understand the basic principles of concrete mix design
and the procedures performed to produce quality
concrete.
CONCRETE BATCH PLANT
SUPERVISOR RESPONSIBILITIES
When assigned as the supervisor of a concrete batch
plant in the NCF, you supervise the production and
transport of concrete products used to construct
sidewalks, roads, footers, foundations, walls, roofs,
runways, rapid runway repairs, and so forth.
PORRLAND CEMENT
Portland cement is usually made of materials,
such as limestone or marl and shale or clay. The raw
materials are crushed, pulverized, and mixed in
proper proportions for the correct chemical
composition. Then, the raw material is fed into a
rotary kiln and is calcined (burned) at a temperature
of approximately 2700°F. This process transforms the
material into a clinker. The clinker is cooled and
pulverized so fine that nearly all of the powder can
pass through a No. 200 mesh sieve.
Types of Cement
When powdered Portland cement and water are
combined, hydration occurs, The amount of water per
unit weight of cement is called the water-cement ratio
normally given in terms of pounds of water per pounds
of cement. Concrete with a low water cement ratio gains
more strength than cement with a higher water cement
ratio.
There are many types of cement, but only the most
common types are listed here:
Type I (normal portland cement) is the most
widely used cement for pavements, sidewalks,
buildings, bridges, masonry units, and soil-cement
mixtures. In general, it is used when the concrete will
not be subjected to special sulfate hazards or where the
heat generated by the hydration of the cement does not
cause an objectionable rise in temperature.
Type II (modified portland cement) has a lower
heat of hydration than Type I. This lower heat gives this
cement an improved resistance to sulfate attack. Type II
cement is used in large structures where cement of
moderate heat of hydration tends to minimize a rise in
temperature. Examples are as follows: large piers, heavy
abutments, heavy retaining walls, and when the concrete
is placed in warm weather. Type 11 cement is also used
in drainage structures where the sulfate concentrations
are higher than normal.
Type III (high-early-strength portland cement) is
used when superior strength is required in a short time.
It is used in cold-weather construction to reduce the
period of protection against low temperatures. Type III
is also used when forms have to be removed
immediately to allow the concrete to be put in service
as quickly as possible. Type III cement requires less
protection time from freezing and attains normal 3-day
strength in 1 day. The volume of heat during hydration
is also accelerated. Normally, this cement is not used in
large-scale construction operations because it is very
expensive.
Storage of Cement
Portland cement is a moisture-sensitive material
that must be protected from damp air or moisture.
Cement not protected when in storage sets more slowly
because hydration has already begun; therefore, it has
less strength than portland cement that is kept dry.
Most types of portland cement are shipped in bulk
by rail, truck, or barge. Pneumatic loading and
unloading of the transport vehicles is the usual method
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