Portland Cement
What Is Cement????
Material with adhesive and cohesive properties or any material that binds or unites – essentially like glue

Function Of Cement are
to bind the sand and coarse aggregate together
to fill voids in between sand and coarse aggregate particle
to form a compact mass
Types of Cement
2 types of cement normally used in building industry are as follows:
a) Hydraulic Cement
b) Nonhydraulic Cement
Hydraulic Cement
Hydraulic Cement sets and hardens by action of water. Such as Portland Cement
In other words it means that hydraulic cement are:
“ Any cements that turns into a solid product in the presence of water (as well as air) resulting in a material that does not disintegrate in water.”
Nonhydraulic Cement
Any cement that does not require water to transform it into a solid product.
2 common Non-hydraulic Cement are
a) Lime- derived from limestone / chalk
b) Gypsum
Portland Cement
Chemical composition of Portland Cement:
a) Tricalcium Silicate (50%)
b) Dicalcium Silicate (25%)
c) Tricalcium Aluminate (10%)
d) Tetracalcium Aluminoferrite (10%)
e) Gypsum (5%)
Function :Tricalcium Silicate
- Hardens rapidly and largely responsible for initial set & early strength
- The increase in percentage of this compound will cause the early strength of Portland Cement to be higher.
- A bigger percentage of this compound will produces higher heat of hydration and accounts for faster gain in strength.
Function : Dicalcium Silicate
- Hardens slowly
- It effects on strength increases occurs at ages beyond one week .
- Responsible for long term strength
Function :Tricalcium Aluminate
- Contributes to strength development in the first few days because it is the first compound to hydrate .
- It turns out higher heat of hydration and contributes to faster gain in strength.
- But it results in poor sulfate resitance and increases the volumetric shrinkage upon drying.
- Cements with low Tricalcium Aluminate contents usually generate less heat, develop higher strengths and show greater resistance to sulfate attacks.
- It has high heat generation and reactive with soils and water containing moderate to high sulfate concentrations so it’s least desirable.
Function : Tetracalcium Aluminoferrite
- Assist in the manufacture of Portland Cement by allowing lower clinkering temperature.
- Also act as a filler
- Contributes very little strength of concrete eventhough it hydrates very rapidly.
- Also responsible for grey colour of Ordinary Portland Cement
Manufacturing Of Portland Cement
The 3 primary constituents of the raw materials used in the manufacture of Portland Cement are:
a) Lime
b) Silica
c) Alumina
Lime is derived from limestone or chalk
Silica & Alumina from clay, shale or bauxite
There are 2 chief aspects of the manufacturing process:
First
To produce a finely divided mixture of raw materials – chalk / limestone and clay / shale
Second
To heat this mixture to produce chemical composition
There 2 main process that can be used in manufacturing of Portland Cement that is
i) wet process
ii) dry process
Wet Process
- Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve.
- The mix will be turned into form of slurry by adding 30 – 40% of water.
- It is then heated to about 2750ºF (1510ºC) in horizontal revolving kilns (76-153m length and 3.6-4.8m in diameter.
- Natural gas, petroluem or coal are used for burning. High fuel requirement may make it uneconomical compared to dry process.
Dry Process
- Raw materials are homogenized by crushing, grinding and blending so that approximately 80% of the raw material pass a No.200 sieve.
- Mixture is fed into kiln & burned in a dry state
- This process provides considerable savings in fuel consumption and water usage but the process is dustier compared to wet process that is more efficient than grinding.
Dry Proces & Wet Process
- In the kiln, water from the raw material is driven off and limestone is decomposed into lime and Carbon Dioxide.
limestone ——> lime + Carbon Dioxide
- In the burning zone, portion of the kiln, silica and alumina from the clay undergo a solid state chemical reaction with lime to produce calcium aluminate.
silica & alumina + lime ——> calcium aluminate
- The rotation and shape of kiln allow the blend to flow down the kiln, submitting it to gradually increasing temperature.
- As the material moves through hotter regions in the kiln, calcium silicates are formed
- These products, that are black or greenish black in color are in the form of small pellets, called cement clinkers
- Cement clinkers are hard, irregular and ball shaped particles about 18mm in diameter.
- The cement clinkers are cooled to about 150ºF (51ºC) and stored in clinker silos.
- When needed, clinker are mixed with 2-5% gypsum to retard the setting time of cement when it is mixed with water.
- Then, it is grounded to a fine powder and then the cement is stored in storage bins or cement silos or bagged.
- Cement bags should be stored on pallets in a dry place.
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