Civil Engineering Reference
In-Depth Information
shows the clinker
production process
from raw feed to the
final product.
The clinker is
cooled and then
pulverized. During
this operation a
small amount of
gypsum (Fig. 2-11)
is added to regulate
the setting time of
the cement and to
improve shrinkage and strength development properties
(
Lerch 1946
and
Tang 1992
). In the grinding mill, clinker is
ground so fine that nearly all of it passes through a 45
micrometer (No. 325 mesh) sieve. This extremely fine gray
powder is portland cement (Fig. 2-1).
ASTM C 1157,
Performance Specification for Hydraulic
Cements,
provides for six types of portland cement as
discussed under “Hydraulic Cements” below.
A detailed review of ASTM C 150 and AASHTO M 85
cements follows.
Type I
Fig. 2-11. Gypsum, a source of sulfate,
is interground with portland clinker to
form portland cement. It helps control
setting, drying shrinkage properties,
and strength development. (60505)
Type I portland cement is a general-purpose cement suit-
able for all uses where the special properties of other types
are not required. Its uses in concrete include pavements,
floors, reinforced concrete buildings, bridges, tanks, reser-
voirs, pipe, masonry units, and precast concrete products
(Fig. 2-12).
Type II
Type II portland cement is used where precaution against
moderate sulfate attack is important. It is used in normal
structures or elements exposed to soil or ground waters
where sulfate concentrations are higher than normal but
not unusually severe (see Table 2-2, and Figs. 2-13 to Fig.
2-15). Type II cement has moderate sulfate resistant prop-
erties because it contains no more than 8% tricalcium
aluminate (C
3
A).
Sulfates in moist soil or water may enter the concrete
and react with the hydrated C
3
A, resulting in expansion,
scaling, and cracking of concrete. Some sulfate compounds,
such as magnesium sulfate, directly attack calcium silicate
hydrate.
Use of Type II cement in concrete must be accompa-
nied by the use of a low water to cementitious materials
ratio and low permeability to control sulfate attack. Fig.
2-13 (top) illustrates the improved sulfate resistance of
Type II cement over Type I cement.
Concrete exposed to seawater is often made with
Type II cement. Seawater contains significant amounts of
sulfates and chlorides. Although sulfates in seawater are
capable of attacking concrete, the presence of chlorides
inhibits the expansive reaction that is characteristic of
sulfate attack. Chloride competes with sulfate for the
aluminate phases, after which they exist together in the
TYPES OF PORTLAND CEMENT
Different types of portland cement are manufactured to
meet various normal physical and chemical requirements
for specific purposes. Portland cements are manufactured
to meet the specifications of ASTM C 150, AASHTO M 85,
or ASTM C 1157.
ASTM C 150,
Standard Specification for Portland Cement,
provides for eight types of portland cement using Roman
numeral designations as follows:
Type I Normal
Type IA Normal, air-entraining
Type II Moderate sulfate resistance
Type IIA Moderate sulfate resistance, air-entraining
Type III High early strength
Type IIIA High early strength, air-entraining
Type IV Low heat of hydration
Type V High sulfate resistance
AASHTO M 85,
Specification for Portland Cement,
also
uses type designations I through V for portland cement. The
requirements of M 85 are almost identical to ASTM C 150.
AASHTO specifications are used by some state depart-
ments of transportation in lieu of ASTM standards.
Fig. 2-12. Typical uses for normal or general use cements include (left to right) highway pavements, floors, bridges, and
buildings. (68815, 68813, 63303, 68809)
