CEMENT
Cement is an important synthetic material. It is the chief component of building materials. Chemically, cement is a mixture of calcium silicate and calcium aluminate, with small amout of gypsum salt.
The essential raw materials used in the manufacture of cement are clay and lime stone. Gypsum (calcium sulphate) is used to regulate setting rate.
Note
Cement resembles a type of lime stone available in port land. J. Aspadin gave the name port land cement in 1824.
Manufacture of cement :
Setting and curing : Cement sets into a hard mass when mixed with water. Therefore it makes an excellent binding material in construction work. The mixture of sand and cement along with water undergoes many complex changes. The first stage of setting takes place within 24 hours after adding water to the cement. The second stage of setting requires about two weeks.
The subsequent setting of cement is achieved by adding water. The method of hardeing cement by treating it with water is known as curing. During curing cement absorbs water. Calcium silicate and aluminates of cement are converted into a colloidal gel. This process is exothermic and hence it requires continuous water treatment.
Cement concrete
The mixture of cement, gravel and sand in the ratio of 1:2:4 or 1:3:6 is known as concrete. An iron skeleton inside concrete gives mechanical strength to the structure.
Cement is an important synthetic material. It is the chief component of building materials. Chemically, cement is a mixture of calcium silicate and calcium aluminate, with small amout of gypsum salt.
The essential raw materials used in the manufacture of cement are clay and lime stone. Gypsum (calcium sulphate) is used to regulate setting rate.
Note
Cement resembles a type of lime stone available in port land. J. Aspadin gave the name port land cement in 1824.
Manufacture of cement :
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| Manufacture of Cement |
Finely powdered ground clay and limestone are mixed with water. This homogeneous mixture is called slurry. It is introduced into a rotary kiln (Fig). Hot air at Hot air at about 1873K is blown from the lower end of the rotary kiln. Due to high temperature the water present in the slurry evaporates. At this temperature clay and lime stone combine chemically to form cement balls.
1. Slurry tank
2. Vapourising zone
3. Rotary kiln
4. Combustion zone
5. Hot air
6. Clinker collector
The cement balls so formed are called clinkers. Clinkers. Clinkers are taken out of the kiln and cooled. Clinkers are then finely powdered by grinding and mixed with 3% gypsum. Gypsum slows down the rapid setting of cement.
1. Slurry tank
2. Vapourising zone
3. Rotary kiln
4. Combustion zone
5. Hot air
6. Clinker collector
The cement balls so formed are called clinkers. Clinkers. Clinkers are taken out of the kiln and cooled. Clinkers are then finely powdered by grinding and mixed with 3% gypsum. Gypsum slows down the rapid setting of cement.
Setting and curing : Cement sets into a hard mass when mixed with water. Therefore it makes an excellent binding material in construction work. The mixture of sand and cement along with water undergoes many complex changes. The first stage of setting takes place within 24 hours after adding water to the cement. The second stage of setting requires about two weeks.
The subsequent setting of cement is achieved by adding water. The method of hardeing cement by treating it with water is known as curing. During curing cement absorbs water. Calcium silicate and aluminates of cement are converted into a colloidal gel. This process is exothermic and hence it requires continuous water treatment.
Cement concrete
The mixture of cement, gravel and sand in the ratio of 1:2:4 or 1:3:6 is known as concrete. An iron skeleton inside concrete gives mechanical strength to the structure.
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Synthetic Materials
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