Portland Cement

History of Cement:

It must interesting to know how cement is made today vis a vis the historical background. Ever since civilizations stepping in the earth, people sought a material that would bind stones into a solid, formed mass. The Assyrians and Babylonians used clay for this purpose, and the Egyptians advanced to the discovery of lime and gypsum mortar as a binding agent for building such structures as the Pyramids. The Greeks made further improvements and finally the Romans developed cement that produced structures of remarkable durability. The secret of Roman success in making cement was traced to the mixing of slaked lime with pozzolana, a volcanic ash from Mount Vesuvius. This process produced cement capable of hardening under water. During the Middle Ages this art was lost and it was not until the scientific spirit of inquiry revived that we rediscovered the secret of hydraulic cement -- cement that will harden under water. Most of the building foundations in the Roman Forum were constructed of a form of concrete, placed in some locations to a depth of 12 feet. The great Roman baths built about 27 B.C., the Coliseum, and the huge Basilica of Constantine are examples of early Roman architecture in which cement mortar was used. Portland cement today, as in Aspdin's day, is a predetermined and carefully proportioned chemical combination of calcium, silicon, iron, and aluminum. Natural cement gave way to portland cement, which is a predictable, known product of consistently high quality. Aspdin established a plant in Wakefield to manufacture portland cement, some of which was used in 1828 in the construction of the Thames River Tunnel. But it was almost 20 years later when J. D. White and Sons set up a prosperous factory in Kent that the portland cement industry saw its greatest period of early expansion, not only in England, but also in Belgium and Germany. Portland cement was used to build the London sewer system in 1859-1867. Thomas A. Edison was a pioneer in the further development of the rotary kiln. In 1902, in his Edison Portland Cement Works in New Village, NJ, he introduced the first long kilns used in the industry-150 feet long in contrast to the customary 60 to 80 feet. Today, some kilns are more than 500 feet long. Parallel improvements in crushing and grinding equipment also influenced the rapid increase in production. Since grinding process consumes most of the energy various grinding systems like ball mill/vertical roller mill/Roller presses has been the result of technological developments. Blending takes place in silos with air blown in from the bottom to aerate the contents. Various new designs were also developed to increase the efficiency of mixing.

1.    Crushing Section:- The raw materials mainly limestone, clay, coke are crushed in the separate crushers and stored automatically into the respective silos.

2.    Storage & Proportioning:- The different raw materials are extracted from the silos in the desired proportion through table feeders and conveyed to raw mill.

3.    Raw Milling:- The raw mix is ground into a Ball Mill at desired fineness to produce Raw Meal, and transported for Homogenizing.

4.    Blending & Homogenization:- The raw meal is homogenized in the blending silos, and is stored automatically into a storage silo for feeding to the kiln.

5.    Palletizing & Burning:- The nodules are made into a nodulisor and charged into the kiln for burning. The clinker after discharge is stored in the clinker yard through deep Bucket Elevator.

6.   Clinker/gypsum crushing, storage & proportioning:- Clinker & Gypsum after crushing stored into the hoppers and extracted in the desired proportion with the help of table feeders and transported to the Cement mill Hopper.

7.    Cement Milling:- The clinker & Gypsum mix is ground in the cement mill to produce cement.

8.    Storage & Packing:- The cement is stored into the cement silos and aerated, tested and packed for dispatch.

Ordinary Portland Cement(OPC):
The ordinary portland cement is popularly known as grey cement which is produced by grinding clinker with 5% gypsum . It is used in all general concreate construction, mass and reinforced concreate. It accounts for about 70.60% of the total production

Portland Pozolona Cement(PPC):
It is cheaply manufactured because it uses flyash /burntclay/ coal waste as the main ingredient. PPC has a lower heat of hydration which isd of advantage in preventing cracks where large volumes are being cast. PPC accounts for 18.3% of the production

Portland Blast Furnace slag cement(PBFSC):

It is made by grinding granulated blast furnace slag,stell industry by product (upto 65%),gypsum 5% and clinker(balance). PBFSC has a heat of hydration even lower than PPC and is generally used in construction of dams and similar massive construction. It contributes nearly 10% to the total.

White Cement:

Basically it is OPC: Clinker using fuel oil (instead of coal) and with iron oxide content below 0.4% to ensure whiteness. Special cooling technique is used. It is used to enhance aestheic value, in tiles and for flooring. White cement is much more expensive than grey cement.

Specialised Cement:

Oil Well Cement :is made from clinker with special additives to prevent any porosity. Rapid Hardening Portland Cement : It is similar to OPC, except that it is ground much finer, so that on casting the compressible strength increases rapidly. Water proof Cement: OPC with small portion of calcium stearate or non-saponifibale oil to impart water proofing properties

1. Ordinary Portland Cement (OPC):
Presently Bureau of Indian Standard has classified OPC in three grades based on the strength of cement. These grades are:

• 1. Grade -33-IS-269-1989

• 2. Grade -43-IS-6112-1989

• 3. Grade -53-IS-12269-1987

These types of cement are suited for all modern types of constructions including all kinds of masonry and concrete works such as pre-cast and pre-stressed concrete. They are also suitable for all kinds of repair works in masonry and concre The higher the grade of cement used , the greater would be the economy , durability and technical advantages . Moreover construction time is also reduced.

 Blended cement:
It is obtained by mixing portland clinker , gypsum and other insert materials in suitable proportions and grinding the mixture to get a thorough and intimate mix.

• Portland Pozzolana Cement (PPC) - Clinker +Gypsum+Pozzolana (Flyash, burnt clay etc)

• Portland blast furnace slag -Cement Clinker +Gypsum+granulated slag

• Masonry Cement -Cement Clinker +Gypsum+Pozzolana (Limestone Powder admixtures etc.

2) PPC: Suitable for most of the applications as stated in OPC ideally suited for domestic consumption like plastering, brickwork, mass concreting works like dams, large foundation. This cement enchances the impermeability and cohesiveness of concrete. As a result durability is enhanced. It also generates low heat of hydration.
It is cheaply manufactured because it uses flyash /burntclay/ coal waste as the main ingredient. PPC has a lower heat of hydration which isd of advantage in preventing cracks where large volumes are being cast. PPC accounts for 18.3% of the production

3.Slag Cement:
Common application are similar to those of OPC. However besides that it has more sulphate resistance properties than OPC and is suitable for coastal construction.
It is made by grinding granulated blast furnace slag,stell industry by product (upto 65%),gypsum 5% and clinker(balance). PBFSC has a heat of hydration even lower than PPC and is generally used in construction of dams and similar massive construction. It contributes nearly 10% to the total.

4.Masonry Cement:
Exclusively meant for masonry works and plaster only.

5.Low heat portland Cement:
Grinding and chemical composition are similar to those of OPC. All applications requiring very high early strength, very high early removal of form works, very high handling of pre-cast element, high grade precast and prestressed concrete product, slipform, cooling tower and prill tower.

6. Sulphate resistant cement:
The chemical composition is designed in such a manner that C3A content in cement restricted to 5% and other chemical constituents are similar to OPC. Used in structures in contact with soil or water having enough sulphate concentration.

7. Oil well cement:
This is a special kind of cement for use in the drilling of wells to fill the space between the steel lining tubes and the well wall. Its sets slowly in order to give the slurry made with it sufficient time to reach the large depths of the oil wells. However once set it develops strength rapidly and remains stable at high temperature.

8. White cement:
It is primarily used for decorative processes and also manufacture of titles. The raw materials are so chosen that the maximum iron-oxide content is strictly limited to 1%. Variety of colours can be obtained by the addition of pigments.

9. Super sulphate cement:
Super sulphate cement is made by intergrinding, a mixture of 80-85% selected granulated slag with 10-15% calcium sulphate and about 5% of portland clinker. It may be applied where high sulphate, acid and organic oil attacks on structure is expected.

10. High alumina cement:
The chemical composition is designed in such a manner that the total alumina content is at least 32%. This cement is ideally suited for high temperature castable refractory.

11. Grey Portland cement:
Chemical composition is similar to OPC except the following limitations which ensures very early strength, increased cohesiveness and increased durability factor towards chemical attack . All applications where high-strength concrete is required ideally suited for railway prestressed concrete sleepers, bridges and slipform construction .

Chemical Composition :