SECTION I. CEMENTS
2-2. Portland cement contains lime and clay minerals (such as limestone, oyster shells, coquina shells, marl, clay, and shale), silica sand, iron ore, and aluminum.
2-3. The raw materials are finely ground, carefully proportioned, and then heated (calcined) to the fusion temperature (2,600 to 3,000 degrees Fahrenheit [F]) to form hard pellets called clinkers, which are ground to a fine powder. Because the powder is extremely fine, nearly all of it will pass through a number 200 sieve (200 meshes to the linear inch or 40,000 openings per square inch). Regardless of the manufacturer, portland cement is the standard for the trade.
AMERICAN SOCIETY FOR TESTING AND MATERIAL (ASTM) TYPES
2-4. ASTM specifications cover five types of portland cements in ASTM C150.
2-5. Type I cement is a general-purpose cement for concrete that does not require any of the special properties of the other types. It is intended for concrete that is not subjected to a sulfate attack or when the heat of hydration will not cause minimum temperature rise. It is used in pavement and sidewalk construction. It reinforces concrete buildings and bridges, railways, tanks, reservoirs, sewers, culverts, water pipes, masonry units, and soil-cement mixtures. Type I cement will reach its design strength in 28 days and is more available than other types.
2-6. Type II cement is modified to resist a moderate sulfate attack. It usually generates less heat of hydration and at a slower rate than Type I cement. Typical applications are drainage structures where the sulfate concentrations in either the soil or ground waters are higher than normal but not severe; large structures produces only a slight temperature rise in the concrete that moderately affects the heat of hydration. However, temperature rise can be a problem when concrete is placed in warm weather. Type II cement will reach its design strength in 45 days.
2-7. Type III cement is a high-early-strength cement that produces design strengths at an early age, usually seven days or less. It has a higher heat of hydration and is ground finer than Type I cement. Type III cement permits fast form removal and in cold weather construction, reduces the period of protection against low temperatures. Although richer mixtures of Type I cement can obtain high early strength, Type III cement produces it more satisfactorily and more economically. Use this material cautiously in concrete structures having a minimum dimension of 2 1/2 feet or more; the high heat of hydration can cause shrinkage cracking.
2-8. Type IV cement is unusual in that it has a low heat of hydration. It is intended for applications requiring a minimal rate and a minimal amount of the heat of hydration. Its strength also develops at a slower rate than the other types. Type IV cement is used primarily in very large concrete structures, such as gravity dams, where the temperature rise from the heat of hydration could damage the structure. It will reach its design strength in 90 days.
2-9. Sulfate resistant cement (Type V) is used mainly where the concrete is subject to severe sulfate action, such as when the soil or ground water contacting the concrete has a high sulfate content. Type V cement will reach its design strength in 60 days.
OTHER ASTM CEMENTS
2-10. ASTM specifications cover the following specific types of portland cements:
Air-Entraining Portland Cement
2-11. Cement types IA, IIA, and IIIA correspond in composition to cement types I, II, and III, respectively, with the addition of small quantities of air-entraining materials interground with the clinker during manufacturing. Especially useful for sidewalks, air-entraining portland cements produce concrete having improved resistance to freeze-thaw action and to scaling caused by snow and ice removal chemicals. Such concrete contains extremely small (as many as 3 billion per cubic yard), well-distributed, and completely separate air bubbles.
White Portland Cement
2-12. White portland cement is a white-finished concrete product used mainly for architectural purposes.
Portland Blast-Furnace Slag Cement
2-13. Cement types IS and IS-A are used in ordinary concrete construction. During manufacturing, granulated blast-furnace slag is either interground with the portland-cement clinker or blended with the ground portland cement. Cement type IS-A contains an air-entraining additive.
Portland Pozzolana Cement
2-14. During the manufacturing of cement types P, IP, PA, and IP-A, pozzolana (containing silica and alumina) is blended with the ground portland-cement clinker. Types PA and IP-A also contain an air-entraining additive. Finely divided siliceous aluminous material reacts chemically with slake and lime at an ordinary temperature and in the presence of moisture, forms a strong slow-hardening cement.
2-15. Masonry cements (also called mortar cement) are a typical mixture of portland cement, hydrated lime, and other materials that improve workability, plasticity, and water retention.
SPECIAL PORTLAND CEMENTS
2-16. Other special types of portland cement not covered by ASTM specifications include--
Oil-well portland cement. It hardens at the high temperatures that prevail in very deep oil wells.
Waterproofed portland cement. It contains water-repellent materials that are ground with the portland-cement clinker.
Plastic cement. It contains plastic agents that are added to the portland-cement clinker; it is commonly used to make plaster and stucco.
PACKAGING AND SHIPPING
2-17. Cement is shipped by railroad, truck, or barge in standard sacks weighing 94 pounds, or in bulk. Cement quantities for large projects may be stated in tons.
2-18. Portland cement retains its quality indefinitely if kept dry. Store-sacked cement in an airtight warehouse or shed. If no shed is available, place the sacks on raised, wooden platforms. Place them close together to reduce air circulation and away from exterior walls. Sacks stored outside for long periods should be covered with tarpaulins or other waterproof coverings so that rain cannot reach either the cement or the platforms. Rain-soaked platforms can damage the bottom layers of the sacks. Cement should be free-flowing and free from lumps when used. Stored, sacked cement sometimes develops warehouse pack. This is a slightly hardened condition caused by packing sacks extremely tight or excessively high. Such cement still retains its quality and is usually restored to a free-flowing condition by rolling the sacks on the floor. However, cement sometimes does develop lumps that are difficult to break up; the cement should be tested to determine its quality. Hard lumps indicate partial hydration that reduces both the strength and durability of the finished concrete. Do no use partially hydrated cement in structures where strength is a critical factor. Store bulk cement in weatherproof bins.
|David L. Heiserman, Editor||
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Revised: June 06, 2015