Civil Engineering Reference
In-Depth Information
Clay
Individual material silos
Vibrating
screen
Limestone quarry
Material proportioning
Primary
crusher
Secondary
crusher
To dry or wet processing
Dry Process
Wet Process
Input from initial processing
Input from
initial
processing
Vibrating
screen
Oversize
material
Air
separator
Ground
raw
material
silos
Dry
mixing
and
blending
Oversize
material
Storage
basin
Slurry
Grinding mill
Grinding mill
Water
addition
To kiln or
optional heating
To kiln
Slurry mixing
and blending
Fines
Optional heating for
dry process
Input
feed
stock
Hot gases
from kiln
heat
Input from dry
processing
Clinker
silo
Gypsum
silo
Kiln
Clinker
cooler
Preheater
Clinker &
Gypsum
proportioning
Oversize
material
Air
separator
Flash
furnace
Finished
Portland
cement
bulk storage
To bulk
shipping or
packing
plant
Grinding mil
l
To kiln
FIGURE 6.1
Steps in the manufacture of portland cement.
stock, with the exhaust gas from the kiln. In addition, some plants use a flash
furnace to further heat the feed stock. Both the preheater and flash furnace im-
prove the energy efficiency of cement production. In the kiln, the raw materi-
als are melted at temperatures of 1400
°
C to 1650
°
C (2500
°
F to 3000
°
F), changing
the raw materials into cement
clinker.
The clinker is cooled and stored. The
final process involves grinding the clinker into a fine powder. During grinding,
a small amount of gypsum is added to regulate the setting time of the cement
in the concrete.
The finished product may be stored and transported in either bulk or
sacks. In the United States, a standard
sack
of cement is 94 lb, which is ap-
proximately equal to of loose cement when freshly packed. The cement
can be stored for long periods of time, provided it is kept dry.
1 ft
3
6.2
Chemical Composition of Portland
Cement
The raw materials used to manufacture portland cement are lime, silica,
alumina, and iron oxide. These raw materials interact in the kiln, forming
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