Portland cement is an excellent construction material commonly used for its excellent binding properties that give strength to structural elements.
PPC cement is finer than ordinary Portland cement and due to pozzolanic action; it improves the pore size distribution and also reduces the micro-cracks at the transition zone.
Portland cement comes in three major categories- Ordinary Portland Cement, Portland Slag Cement, Portland Pozzolana Cement.
Manufacturing of Portland cement:
The cement manufacturing process can be divided into three distinct stages as follows;
1) Raw material acquisition:
The raw materials required for the manufacture of Portland cement are calcareous (such as limestones and chalks) and argillaceous material, such as shales, slates or clays.)
2) Clinker production:
Clinker is produced in a Kiln.
Grinding, mixing and burning of raw materials at a temp. 1400 – 1500° C.
Clinker is produced in a kiln in the form of dark greenish-blue balls.
3) Cement grinding, packing and distribution:
The clinker is cooled and ground to a fine powder by adding 3 to 5% gypsum.
Then packing and storage of the product.
The product formed using this process is Portland cement.
There are two types of process for manufacturing of cement:
Wet manufacturing process:
i) In this method, mixing and grinding of raw materials is done in a wet state.
ii) All raw materials are transported to a ball mill or tube mill and ground to a consistent consistency of the solution with the addition of water.
iii) The solution is tested to give the required chemical composition and correct it from time to time.
iv) Finally, the modified slurry is stored in the final storage tank.
v) The corrected slurry is fed into Rotary kiln, where at 1500 °C temperature given to the slurry to form with the clinker.
vi) The clinker falls into the rotary cooler & it is cooled under controlled conditions.
vii) Cooled clinker is added to a ball mill of 3 to 5% gypsum to prevent flash-setting of cement.
viii) Then portland cement is stored in cement – silos and finally dispatched or filled into barrels for bulk supply to dams or other large works.
Dry manufacturing process :
i) In this method, the raw material is dried and crushed and fed to the grinding mill in the correct proportion.
ii) The raw materials used for cement manufacture are limestone and clay.
iii) The dry powder called raw metal is then re-mixed and corrected for its correct composition and mixed through compressed air.
iv) The mixture is fed into a large rotary kiln in which it is heated to a temperature of 1450 °C in a dry state.
v) The chemical reaction in kiln causes the material to aggregate into clinker.
vi) The hot clinker is then cooled up to 100 °C at which it can easily be stored in clinker silos.
vii) Then add 3 to 5 % gypsum to form a fine powder and retard the setting time and finally dispatched in a bag of 50 kg.
Portland Cement Properties:
Following are the ill-effects of ingredients of cement if it is used in excess amount;
Deficiency of lime causes a decrease in the strength of cement and excess free lime causes unnecessary expansion and disintegration of cement.
Proper percentage of lime maintains the binding property of cement.
During the manufacturing of cement, silica undergoes a chemical reaction with calcium to form di-calcium and tri-calcium silicates which adds the strength to the cement.
The high amount of silica provides strength to the cement, but its setting time is delayed.
A large amount of alumina accelerates the setting but weakens the cement.
iv) Iron Oxide:
The high volume of iron oxide will make the cement difficult to fuse and form clinker.
High ferric oxide content is favourable to the production of high early strengths in cement.
The magnesium content shall not exceed 5.0 % by mass.
Excess magnesia makes the cement unsound.
vi) Sulphur Trioxide:
Excess quantity of sulphur trioxide also makes the cement unsound.
The large quantity of alkalies causes efflorescence.
Cement with lower alkali content has caused objectionable expansion.
During the grinding process, a small quantity of gypsum is added.
Gypsum supersedes the setting time of cement.
Types of Portland cement:
Type I: For general purpose
Type IA: It is Similar like Type I, but when air entrainment is desired.
Type II: For moderate sulfate resistance.
Type IIA: It is same as Type II, but when air entry is desired.
Type II (MH): It is much like Type II, but when moderate heat of hydration is desired.
Type II (MH) A: Similar to Type II (MH), but when air entrainment is desired.
Type III: For high starting power.
Type IIIA: Alike to Type III, but when air entrainment is desired.
Type IV: For low heat of hydration.
Type V: for high sulfate resistance.
Advantages of portland cement:
- It has great resistance to cracking and shrinkage.
- The initial setting of OPC is faster than that of PPC, so it is suggested in projects where props are to be removed initially.
- The treatment period of OPC is shorter than PPC and the cost of treatment is reduced, therefore recommended where the cost-prohibitive treatment will occur.
Disadvantages of portland cement:
- It cannot be used for large-scale concreting because it has a higher heat of hydration than PPC.
- The durability of OPC is lower than the PPC.
- It produces relatively less solid concrete than PPC, so pumping the concrete becomes a bit difficult.
- The OPC is low in finer detail, hence higher permeability and consequently lower durability.
- OPC is expensive than PPC.
Portland Cement Uses:
- It is used for general construction purposes, where special properties are not required, like reinforced concrete buildings, bridges, etc.
- Also used in most concrete masonry units.
- It is also used as a basic component in a mortar, plaster, and non-speciality grout.
Frequently Asked Questions:
Why is it called Portland cement?
In 1824, Joseph Aspin, a brick-making company in Leeds, England, took out a patent on hydraulic cement and called it Portland cement.
What is Portland cement used for?
Portland cement is used to make almost all concrete.
How long does portland cement last?
What is Portland cement good for?
It is excellent binding properties giving strength to structural elements.
Portland cement is a complex product derived from unprocessed common natural materials: limestone and clay.
Therefore it is necessary for the cement industry to produce clinker that would facilitate the production of low w/c concretes that are more durable than general strength concretes.