The type of Portland cement used in a concrete structure determines the time it will take to harden, and also its final strength. Learn about all such types, in this HomeQuicks article, which also tells you about their different uses.
Did You Know?
Type I and II are the most common types of Portland cement in the US. Together, they account for more than 92% of the total cement production.
Portland cement, contrary to popular belief, is not a brand of cement, but the most common type which is used as an ingredient in concrete and mortar all around the world. There are a number of uses for cement, and since each use is unique, it needs a different type of cement. The American Society for Testing and Materials (ASTM) classifies Portland cement into different types, based on the proportion of chemicals in each one. The most common chemical constituents used to classify Portland cement are C3A (tricalcium aluminate), C3S (tricalcium silicate), C4AF (tetracalcium aluminoferrite), and a concept called the ‘heat of hydration’.
Having a higher percentage of C3A, cement sets quickly, and releases a high heat of hydration. C3S gives the cement its initial strength, and makes it harden rapidly. On the other hand, C4AF has little to do with strength, but imparts the gray color to ordinary Portland cement. ‘Heat of hydration’ is the term used to describe the heat released when cement reacts with water during the formation of concrete. Having understood these terms, let us now check out the various types of Portland cement.
Also called Ordinary Portland Cement (OPC), Type I is a general-purpose cement, which is adequate for most uses, except those which require the special properties of other types. It has an adequate strength and a low heat of hydration. Type I cement is not suitable for uses where the concrete can face chemical attacks, or excessive temperature during curing. It can be used in applications like precast concrete products, reinforced buildings, floors, bridges, reservoirs, tanks, culverts, sewers, pavements, sidewalks, pipes, etc.
Type II has the same uses as Type I, along with a moderate resistance to sulfates. It generates only a moderate heat of hydration, and at a lesser rate. It is ideal for applications where the concrete comes into contact with soils or groundwater having some amount of sulfate ions, though not excessively high. It’s low concentration of C3A, which is lesser than 8%, imparts this resistance to sulfate attack. It is common in parts of western USA and Canada which have such sulfate-rich conditions. It is ideal for heavy structures like abutments, piers, and retaining walls.
Type III cement is chemically almost identical to Type I, though it has a lesser curing time, which means it hardens faster. It is also ground finer, and contains a higher amount of C3S, both of which promote the rapid setting of concrete. This type imparts strength faster than Type I, typically in less than a weeks time, though its final 28-day strength may be equal, if not lesser. It is ideal for applications which require quick setting, so that structures can become operational faster, and where formwork needs to be removed and reused. It is also ideal for cold areas, where the quick curing of concrete prevents damage due to frost.
This type of Portland cement is designed to reduce the heat released during hydration. This is achieved by reducing the percentage of C3A in the cement. However, this type has a lower final and initial strength as compared to Type I. It is suited for the construction of massive structures with a low surface-to-volume ratio, like gravity dams, where a large heat of hydration may result in dangerous cracks. This type of cement is not commonly manufactured or available for sale, and is mostly supplied for bulk orders.
This is almost similar to Type II, except that it is even more tolerant to the attack of sulfate ions. This is achieved by reducing the C3A percentage even lower to 5%. So, it is suitable for buried concrete structures, where the soil or groundwater is rich in sulfate ions. However, it gains strength at a slow rate as compared to Type I (OPC). Like Type II, it is more common in the western United States and Canada. It is used for applications like canal linings, retaining walls, and culverts, which may be exposed to a sulfate attack.
Type Ia, IIa, IIIa
These types are almost identical to the basic I, II, and III types, respectively, except that they contain small amounts of air-entrainment admixtures which are blended with the cement during its manufacture. These mixtures form small air bubbles inside the concrete block when it sets, which is ideal for cold temperatures, where freeze-thaw cycles can produce cracks in the concrete. The smaller water-cement ratio also increases the workability of the cement.
White Portland Cement
It is similar to Type I Portland cement, except that it is white in color. This is achieved by reducing the percentage of iron (C4AF) and magnesium oxide, which impart a gray color to ordinary Portland cement. Since it requires additional care in the choice of ingredients, and to produce white color, this type is complex and expensive to manufacture. It is ideal for applications like precast curtain walls, facing panels, stucco, terrazzo surface, cement paint, and white/colored concrete and mortar.
While these are the most common types of Portland cement, certain hybrids like I/II or II/V are also used. These hybrids meet the requirements of both types, and can be used for the applications of either one.