Types of Portland cement
General
There are different standards for classification of portland cement. The two
major standards are the American ASTM C150 and European EN-197. EN 197 cement
Types CEM I, II, III, IV, and V do not correspond to the cement types in ASTM C
150, nor can ASTM cements be substituted for EN specified cement, without the
designer’s approval.
ASTM C150
There are five types of Portland cements with variations of the first three
according to ASTM C150. ASTM stands for the American Society of Testing
Materials and is basically a manual for all materials and their properties and
proper uses. In addition, pozzolanic ash or other pozzolans are often added to
cement to improve its properties and lower its cost.
Type I Portland cement is known as common cement. It is generally assumed unless
another type is specified. It is commonly used for general construction
especially when making precast and precast-prestressed concrete that is not to
be in contact with soils or ground water. The typical compound compositions of
this type are:
55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% Ignition
loss, and 1.0% free CaO.
A limitation on the composition is that the (C3A) shall not exceed fifteen
percent. This type is the most basic and common type of Portland cement.
Type II is known to have moderate sulfate resistance with or without moderate
heat of hydration. This type of cement costs about the same as Type I. Its
typical compound composition is:
51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8% Ignition
loss, and 1.0% free CaO.
A limitation on the composition is that the (C3A) shall not exceed eight percent
which reduces its vulnerability to sulfates. This type is for general
construction that is exposed to moderate sulfate attack. This is meant for use
when concrete is in contact with soils and ground water especially in the
western United States due to the high sulfur content of the soil. Another
limitation is the percentage of (C3S) + (C3A) shall not exceed 58. The two
limitations are meant to minimize cracking caused by temperature gradients.
Note: Cement is increasingly sold as a blend of Type I/II on the world market.
Type III is known for its high early strength. Its typical compound composition
is:
57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% Ignition
loss, and 1.3% free CaO.
This cement is produced grinding clinker, bonded cement chunks, with a high
percentage of (C3A) and (C3S) into a finer texture. The gypsum level is also
increased a small amount. This gives the concrete using this type of cement a
three day compressive strength equal to the seven day compressive strength of
types I and II. Its seven day compressive strength is almost equal to types I
and II 28 day compressive strengths. The only downside is that the six month
strength of type III is the same or slightly less than that of types I and II.
Therefore the long-term strength is sacrificed a little. The highly early
strength is gained by increasing the tricalcium silicate, (C3S), in the mix.
This increased amount of tricalcium silicate brings the danger of free lime in
the cement and high volume changes after setting. Type III can also be used in
concrete that comes in contact with soil and ground water. It is usually used
for emergency construction and repairs and construction of machine bases and
gate installations.
Type IV Portland cement is generally known for its low heat of hydration. Its
typical compound composition is:
28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.9% Ignition
loss, and 0.8% free CaO.
The percentages of (C2S) and (C4AF) are relatively high and (C3S) and (C3A) are
relatively low. This causes the heat given off by the hydration reaction to
develop at a slower rate. However, as a consequence the strength of the concrete
develops slowly. After one or two years the strength is higher than the other
types after full curing. This cement is used for very large concrete structures,
such as dams, which have a low surface to volume ratio. This type of cement is
generally not in stock and has to be special ordered in large quantities. A
limitation on this type is that the maximum percentage of (C3A) is seven, and
the maximum percentage of (C3S) is thirty-five. Another negative about this type
of cement is its higher cost. Recently mix designs using pozzolans and
water-reducing admixtures have been developed to decrease the cement content
which has allowed for Type II Portland cement to be substituted in for Type IV
in the production of dams. This helps lower the cost of the dam.
Note: Type IV cement is not really used any in industry.
Type V is known for its sulfate resistance. Its typical compound composition is:
38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.9% Ignition
loss, and 0.8% free CaO.
This cement has a very low (C3A) composition which accounts for its high sulfate
resistance. The maximum content of (C3A) allowed is five percent for type V
Portland cement. This type is used in concrete that has a tendency to be exposed
to alkali soil and ground water sulfates. It is generally not meant for use
around seawater, but it can be done as long as the (C3A) composition is above
two percent. It usually requires an advance order and is generally available to
the western United States and Canada. Another limitation is that the (C4AF) +
2(C3A) composition cannot exceed twenty percent. This type of cement is
essential in the construction of canal linings, culverts, and siphons because of
their contact with ground waters containing sulfates. This is required because
sulfates cause serious deterioration and swelling to the other types of Portland
cement. The serious deterioration will eventually cause the concrete to fail.
Type V Portland cement is a very uncommon type used in everyday construction but
is routinely used in harsh marine environments.
Types Ia, IIa, and IIIa have the same composition as types I, II, and III. The
only difference is that in Ia, IIa, and IIIa an air-entraining agent is ground
into the mix. The air-entrainment must meet and minimum and maximum optional
specification found in the ASTM manual. These types are only available in the
eastern United States and Canada but can only be found on a limited basis. They
are a poor approach to air-entrainment which improves resistance to freezing
under low temperatures.
EN 197
EN 197-1 classify Portland cement in 5 classes that differ from ASTM.
I Portland cement Comprising Portland cement and up to 5% of minor additional
constituents
II Portland-composite cement Portland cement and up to 35% of other single
constituents
III Blastfurnace cement Portland cement and higher percentages of blastfurnace
slag
IV Pozzolanic cement Comprising Portland cement and higher percentages of
pozzolana
V Composite cement Comprising Portland cement and higher percentages of
blastfurnace slag and pozzolana or fly ash
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