Cement is an important construction material with extremely ground particles having adhesive and cohesive properties which make it capable of bonding mineral fragments into a compact whole.
In this method, it imparts strength and sturdiness to the hardened mass referred to as concrete. The cement used in the making of concrete is called hydraulic cement – so named, because they have the property of reacting chemically with water in an exothermic process called hydration.
i) Main Ingredients or components of Cement with their functions
We will discuss the main 6 components of cement:
- If the lime is in the right proportion, it makes the cement sound and strong.
- If lime is in excess, it makes cement unsound and causes the cement to expand and disintegrate.
- If the lime is in deficiency, the strength of cement is decreased and cement sets quickly.
2) Silica (SiO2)
- It is responsible for the strength of cement.
- An excessive amount of silica in cement provides greater strength to the cement but at the same time prolongs its setting time.
3) Alumina (Al2O3)
- It is responsible for the quick setting of the cement.
- Also, it acts as a flux and reduces clinkering temperature.
- When present in excess it reduces the strength of cement.
4) Iron Oxide (Fe2O3)
- It provides color, hardness, and strength to the cement.
- It also helps the infusion of raw materials during the manufacture of cement.
5) Magnesium oxide (MgO)
- It also imparts hardness and provides color to the cement.
- Its excess amount makes the cement unsound.
6) Calcium sulphate or Gypsum:
- It acts as a retarder, that is, it prolongs the initial setting time of cement.
- In the absence of gypsum, the cement will set very quickly.
- It will set in a few minutes after mixing with water.
Also, Read: Advantage of PPC compared to OPC
ii) Classification of cement
Cement can be broadly classified as:
1) Natural cement
- It is manufactured from stones containing 20 to 40 percent of clay, the remainder being carbonate of lime mixed with carbonate of magnesia.
- The stones are first burnt and then crushed.
- It possesses a brown color and sets rapidly when mixed with water.
2) Artificial cement
- It is manufactured by burning an appropriately proportioned mixture of calcareous and clay material at very high temperatures (about 1450 degrees Celcius) and then grinding the resulting burnt mixture (clinker) with adding a small percentage of gypsum.
- In an artificial cement initial setting time, final setting time, hardening and rate of evolution of heat can be regulated.
- A common type of artificial cement is known as normal setting cement or Portland cement.
iii) Properties Of Cement
Following are the important properties of cement:
- Provides strength to masonry
- Stiffens or hardens early.
- Possess good plasticity.
- An excellent building material.
- Easily workable.
- Good moisture-resistant.
iv) Uses of Cement
- It is used in cement mortar for masonry work, plastering, pointing, etc.
- It is used for making joints for pipes, drains, etc.
- It is used in concrete for laying floors, roofs and constructing lintels, beams, stairs, pillars, etc.
- It is employed for manufacturing precast pipes, piles, poles, etc.
- It is used in the construction of important civil engineering construction such as bridges, culverts, dams, tunnels, lighthouses, etc.
- It is used in every field of civil engineering construction.
v) Setting And Hardening Of Cement
The chemical reaction between cement and water is called hydration of cement or simply cement hydration.
When cement is mixed with water (varying from 25 to 35 % by weight), a stiff and sticky paste is formed which remains plastic for a short period.
With the passage of your time, the plasticity gradually disappears and the cement paste becomes stiff due to initial hydration of cement.
This phenomenon by virtue of which the plastic cement changes into a solid mass is known as the setting of cement.
On setting, the cement binds the aggregates into a solid mass which gains strength as the time lapses, till the hydration of cement is complete. Thus, the development by virtue of that the cement paste, that is finally set, develops strength is understood as hardening of the cement.
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