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Types of Portland cement
GeneralThere 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. |
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Type I Portland cementType 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: Type II Portland cementType 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 Portland cementType 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 cementType 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 Portland cementType 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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