Types of Portland Cement
Different types of Portland cement are manufactured to meet specific purposes, as outlined by the American Society for Testing and Materials (ASTM) Designation C150, which specifies eight types:
|
Type |
Name |
|
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 |
Type I cement
Type I cement is a general-purpose cement used in various concrete applications such as pavements, floors, reinforced concrete buildings, bridges, tanks, and pipes. It is ideal for concrete not subjected to aggressive exposures like sulfate attack from soil and water or objectionable temperature rises.
Type II cement
Type II cement is utilized in situations where precautions against moderate sulfate attack are necessary, such as in drainage structures exposed to moderate sulfate concentrations from groundwaters. It generates less heat of hydration at a slower rate compared to Type I cement, making it suitable for mass structures like large piers, heavy abutments, and retaining walls. Its lower heat generation also makes it preferable in hot weather.
Type III cement
Similar to Type I cement in chemical and physical composition, Type III cement has finer particles, offering high early strengths usually within a week or less. It is chosen when forms need to be removed quickly or when the structure must be put into service promptly. Type III cement is preferred in cold weather to reduce the curing period.
Type IV cement
Type IV cement is employed where minimizing the rate and amount of heat generated from hydration is crucial. It develops strength at a slower rate compared to other cement types, making it suitable for massive concrete structures like large gravity dams, where controlling temperature rise to prevent concrete cracking is essential.
Type V cement
Type V cement is specifically used in concrete exposed to severe sulfate action, primarily where soils or groundwaters have high sulfate content. Its high sulfate resistance is attributed to its low C3A content of about 4%. However, it is not resistant to acids and other highly corrosive substances.
Air-Entraining Portland Cements
(Types IA, IIA, and IIIA)
These cements have the same composition as Types I, II, and III, respectively, but include small quantities of air-entraining material inter-ground with the clinker during manufacture. They produce concrete with improved resistance to freeze-thaw action and scaling caused by chemicals used for snow and ice removal.
White Portland Cement
White Portland cement shares the same composition as Type I or Type III cement but has a white color instead of gray. It is made from selected raw materials containing negligible amounts of iron and magnesium oxides, which are responsible for cement's gray color. White Portland cement is primarily used for architectural purposes.
Blended Hydraulic Cements
These cements are produced by blending Portland cement with by-product materials such as blast-furnace slag, fly ash, silica fume, and other pozzolanas. ASTM C 596 recognizes five classes of blended cements:
- Portland blast-furnace slag cement (Type IS)
- Portland pozzolana cement (Type IP and Type P)
- Pozzolana-modified Portland cement (Type I(PM))
- Slag cement (Type S)
- Slag-modified Portland cement (Type I(SM))
Masonry Cements
Masonry cements are used in mortar for masonry construction. ASTM C 91 classifies masonry cements into Type N, Type S, and Type M.
Expansive Cements
Primarily used in concrete for shrinkage control, expansive cements are classified by ASTM C 845 as Type E-1(K), Type E-1(M), and Type E-1(S).
Special Cements (Not covered by ASTM)
|
Type |
Uses |
|
1. Oil-well cements |
For sealing oil wells |
|
2.Waterproof Portland cements |
For reducing capillary water transmission |
|
3. Plastic cements |
For making plaster and stucco |
Chemical Compounds in Portland Cement
As indicated earlier the burning operation of the raw materials results into the reaction between the oxides and four compound compositions are formed in the final cement product, as follows:
C3S = 3CaO.SiO2 (Tricalcium silicate)
C2S = 2CaO.SiO2 (Dicalcium silicate)
C3A = 3CaO.Al2O3 (Tricalcium aluminate)
C4AF = 4CaO. Al2O3.Fe2O3 (Tetracalcium aluminoferrite)
Chemical and Compound Composition and Fineness of Some Typical Cements are given in Table 2-4.
Role of Compound Composition
1. C3S
Hydrates and hardens rapidly, contributing to initial set and early strength. Higher percentages of C3S result in higher early strength.
2. C2S
Hydrates and hardens slowly, contributing mainly to strength increase beyond one week.
3. C3A
Liberates a large amount of heat during the initial days of hydration, slightly contributing to early strength. Gypsum added to the cement slows down the hydration rate of C3A. Cements with low percentages of C3A are particularly resistant to soils and waters containing sulfates.
4. C4AF
Does not significantly affect hydration.