What is Cement?
Cement is a binding agent that holds aggregates and reinforcing elements together. For all forms of construction, including dwellings, roads, schools, hospitals, dams, and ports, as well as for decorative purposes and objects like tables, sculptures, or bookcases, cement is mostly employed as a binder in concrete.
What are the Different Types of Cement?
Different types of cement are used in the construction sector. The differences between each type of cement are its properties, uses, and composition materials used during the manufacturing process. The following list includes the most common types of cement used in construction.
- Ordinary Portland Cement
- Quick Setting Cement
- Rapid Hardening Cement
- Low Heat Cement
- Portland Pozzolana Cement
- Portland Blast Furnace Slag Cement
- High Alumina Cement
- Sulphate Resisting Cement
- Hydrophobic Cement
- Super Sulphated Cement
- Expansive Cement
- Air Entraining Cement
- White Cement
- IRS-T40 Cement
Ordinary Portland Cement (OPC)
Ordinary Portland cement is the most extensively manufactured and used cement worldwide, which is suited for all types of concrete construction. It is made of Calcareous materials containing calcium carbonate (limestone, marl) and Argillaceous materials containing clay (clay, shale). Main constituents of OPC are lime (62-67%), silica (17-25%), alumina (3-8%), calcium sulphate (3-4%), iron oxide (3-4%) and magnesia (1-3%).
When cement ingredients are inter-grinded and burned, they fuse together, forming complex compounds known as Bogues compounds. In addition to water, these compounds react with it causing the cement to set and harden. These compounds are listed below –
- Tricalcium Aluminate(C3A) – It is responsible for the flash setting of cement, i.e., it is the first to harden and set.
- Tricalcium Silicate(C3S) – It is responsible for the development of strength in the early stages.
- Dicalcium Silicate(C2S) – It is responsible for the progressive strength of cement in later stages.
- Tetra Calcium Alumino Ferrate(C4AF) – It does not impart any property in the cement and hence, is of no engineering significance.
Types of Ordinary Portland Cement – 33 grade, 43 grade, and 53 grade. The grade signifies the compressive strength of cement at 28 days.
For example, 33 grade means the compressive strength of cement at 28 days is 33 N/mm2.
Properties – OPC resists cracking and dry shrinkage well but is less resistant to chemical attack. Some of the important properties of OPC are listed below -
- Specific Gravity – 3.15
- Density – 1440 kg/m3
- Setting time – Initial setting time should not be less than 30 minutes whereas the final setting time should not be more than 10 hours.
- Fineness – As measured by Blaine’s method, the specific surface area should not be less than 225 m2/kg.
Uses – It is employed in general construction works as well as in the majority of masonry projects.
Quick Setting Cement
Quick Setting Cement is obtained by adding a small percentage of alumina in finely ground cement clinkers and reducing the proportion of gypsum (calcium sulphate). As the name suggests, this type of cement sets very quickly. The initial setting time is just 5 minutes and the final setting time is 30 minutes.
Quick setting cement finds its application in construction where cement is required to set quickly such as:
- Underwater concreting
- In cold and rainy weather conditions
- Grouting operations
Rapid Hardening Cement
Rapid Hardening Cement is a type of cement that has a higher rate of gain of strength as compared to OPC. This cement attains the same strength in 3 days that OPC may attain in 7 days. However, the ultimate strength of the rapid hardening cement is the same as OPC. Higher strength in the early stages is obtained by finely grinding the cement for higher fineness (specific surface area should not be less than 325 m2/kg) and increasing the proportion of C3S.
This type of cement is used in construction works where speedy construction is required. Rapid Hardening Cement finds its application in:
- Pavement construction
- Cold weather concreting
- Repair works in roads and bridges
- Where formworks are to be reutilized for rapid constructions as it allows early formwork removal
Low Heat Cement
Low Heat Cement produces low heat of hydration as compared to normal cement. This type of cement is produced by reducing the proportion of C3A and C3S which causes a reduction in heat of hydration of the cement and reduces early strength. The quantity of C2S is increased to compensate for the loss of strength. Reduction in the proportion of C3A also results in increased initial setting time (60 minutes). This type of cement is resistant to sulphate attacks and is less reactive.
Low heat cement is used for mass concreting in dams and other hydraulic structures, bridge abutments, massive retaining walls, piers, etc. It is also used in the construction of chemical plants.
Portland Pozzolana Cement (PPC)
Portland Pozzolana Cement is prepared by inter-grinding pozzolanic materials with Portland cement. Pozzolanic materials are compounds that do not possess any cementitious property. When finely ground in the presence of water, react with calcium hydroxide released during the hydration of cement and lead to the formation of a cementitious compound. Some examples of Pozzolanic materials are blast furnace slag, rice husk, fly ash, surkhi, etc. This type of cement exhibits the following properties:
- Low cost
- Low heat of hydration
- Higher plasticity
- Reduced permeability
- Higher resistance against expansion
- Higher resistance against chloride and sulphate attacks
Portland pozzolana cement is widely used for the construction of marine and hydraulic structures. Due to its high chemical resistance, this type of cement is also used for the construction of pipes for sewage works.
Portland Blast Furnace Slag Cement
Portland Blast Furnace Slag Cement is prepared by inter-grinding granulated blast furnace slag with OPC clinkers. This type of cement can be utilized for projects where the economy is a major consideration as it is of low cost as compared to OPC. Further advantages include lower heat of hydration and higher durability. It offers high resistance against attacks of sulphur and chlorides, so it can be used in marine works. It also offers lower permeability and hence can be used in water retaining structures.
High Alumina Cement
High Alumina Cement is manufactured by calcination of limestone and bauxite (ore of alumina). This type of cement offers a higher initial setting time (3.5 hours) and a lower final setting time (5 hours). It offers higher early strength. High alumina cement is generally used in furnace lining as it can resist high temperature. It is also utilized where concrete has to resist frost and acidic action.
Sulphate Resisting Cement
OPC is highly susceptible to the attack of sulphates which causes volume change. This volume change leads to the formation of cracks in the structure. Sulphate Resisting Cement is a type of cement in which proportions of C3A are reduced to make the cement more resilient to sulphate attack. This type of cement finds its use in constructions such as marine structures, sewerage systems, foundation works, and pipes laid in marshy areas.
Hydrophobic Cement is produced by inter-grinding ordinary cement clinkers with water repellant film-forming substances such as stearic acid and oleic acid. The water repellant film formed around the cement particles reduces the rate of deterioration of the cement due to prolonged storage under unfavorable conditions.
Super Sulphated Cement
Super Sulphated Cement is prepared by inter-grinding granulated blast furnace slag and a small amount of Portland cement clinkers with the addition of gypsum. The cement offers very high resistance against the attacks of chlorides and sulphates. This type of cement is used when the construction must be done under aggressive conditions. This includes marine works, reinforced concrete pipes in groundwater, mass concreting works to resist the attack by aggressive water, concrete construction in sulphate-bearing soil, and in chemical works subjected to a high concentration of sulphates.
Expansive Cement is produced by mixing sulpho-aluminated clinker with Portland cement with a stabilizer. This type of cement expands slightly over time but does not shrink during or after the hardening process. Expansive cement is frequently used as an essential part of sealing joints for expansion joint cement. It is also used in grouting anchor bolts and the construction of prestressed concrete ducts.
Air Entraining Cement
Air Entraining Cement is prepared by an inter-grinding mixture of OPC clinkers and air-entraining agents such as calcium ligno-sulphate, salts from wood resins, glues, etc. Air entraining cement forms tiny air bubbles which improve workability and reduce the water-cement ratio and in turn cause less shrinkage. It also enhances the frost resistance of concrete.
White Cement is obtained by lowering the iron oxide content in OPC. Except for the color, white cement is very identical to ordinary Portland cement. This cement is expensive as compared to OPC and hence, not used for ordinary works. It is used for decorative works, tile grouting, swimming pools, and terrazzo flooring.
IRS-T40 Cement is a special type of cement used mainly for manufacturing railway sleepers. This unique cement is made according to specifications specified by the Indian Railways Ministry. This cement comprises a high percentage of C3S, which is finely ground to achieve high early strength.
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