Civil Engineering Reference
In-Depth Information
bulk cement. However, the recent introduction of large
sacks holding one to twelve tons of cement provides a new
alternative to bulk cement handling. Bulk cement is meas-
ured by the metric ton (1000 kg) or short ton (2000 lb).
Cement is also bagged for convenient use at construc-
tion sites (Fig. 2-53) and for small jobs. In the United States
a bag of portland cement has a mass of 42 kg (92.6 lb) and
a volume of 28 liters. Traditionally a U. S. bag contains 94 lb
(42.6 kg) and has a volume of one cubic foot. The mass of
masonry cement and mortar cement by the bag is 36 kg for
Type M, 34 kg for Type S, and 32 kg for Type N. Plastic
cement has a mass of 42 kg for Type M and 35 kg for Type
S. All bag weights are based on a 28 liter volume standard.
Information for quantities of blended and specialty
cements can be found on the bag. Partial bag sizes are also
available in some areas.
In Canada, a bag of portland cement has a mass of 40
kg, and in other countries a bag of cement can have a mass
of 25 kg or 50 kg.
Because of the variability of bag sizes and the presence
of supplementary cementitious materials, cement bag
factor terminology, such as “a six bag mix” should not be
used to describe the cement content of concrete mixtures.
In the 1800s and early 1900s, cement was shipped in
barrels; one barrel contained 4 bags (171 kg or 376 lbs or 4
cu ft) of cement. Use of the barrel unit is archaic and should
not be used.
Fig. 2-51. Two-dimensional image of portland cement. Colors
are: red-tricalcium silicate, aqua-dicalcium silicate, green-
tricalcium aluminate, yellow-tetracalcium aluminoferrite,
pale green-gypsum, white-free lime, dark blue-potassium
sulfate, and magenta-periclase. The image was obtained by
combining a set of SEM backscattered electron and X-ray
images (
NIST 2001
).
percolation, porosity, diffusivity, thermal conductivity, elec-
trical conductivity, carbonation, elastic properties, drying
profiles, susceptibility to degradation mechanisms, autoge-
nous shrinkage, and volumes of hydration reactants and
products as a function of time. The effects of varying sulfate
and alkali contents can be examined, along with interaction
with supplementary cementitious materials and chemical
admixtures. Computer modeling predicts performance
without the expense and time requirements of physical
testing (
NIST 2001
).
STORAGE OF CEMENT
Cement is a moisture-sensitive material; if kept dry, it will
retain its quality indefinitely. Cement stored in contact with
damp air or moisture sets more slowly and has less
strength than cement that is kept dry. At the cement plant,
and at ready mixed concrete facilities, bulk cement is stored
in silos. The relative humidity in a warehouse or shed used
to store bagged cement should be as low as possible. All
cracks and openings in walls and roofs should be closed.
Cement bags should not be stored on damp floors but
should rest on pallets. Bags should be stacked close
together to reduce air circulation but should never be
TRANSPORTATION AND PACKAGING
Around 100 million metric tons of cement are shipped per
year throughout the United States. Most portland cements
are shipped in bulk by rail, truck, barge, or ship (Fig. 2-52).
Pneumatic (pressurized air) loading and unloading of the
transport vehicle is the most popular means of handling
Fig. 2-52. Portland cements are shipped from the plant silos to the user in bulk by (left to right) rail, truck, or water. (59899,
59355, 59891)
