Cement
source : chemistry assignment.com
Cement:
It is a mixture of following components:
3Cao . SiO2 (Tri calcium silicate)
2CaO . SiO2 (Di calcium silicate)
3CaO . Al2O3 (Tri calcium Aluminate)
4CaO . Al2O3 . Fe2O3 (Tetra calcium alumino ferrite)
CaSo4 . 2H2O (Gypsum)
Percentage composition :
CaO= 50 – 60%
SiO2 = 20 – 25%
Al2O3 = 5 – 10%
MgO = 2 – 3%
Other oxides = 2 – 4%
Manufacture :
Raw materials required are:
- Lime stone ( CaCO3)
- Gypsum ( CaSO4 . 2H2O)
- Clay ( It is the mixture of SiO2 and Al2O3)
Process :
Lime stone and clay are mixed in proper ratio. These are ground with water. The paste is called slurry. It is heated in rotary kiln. It consists of 30-40 meter long cylinder and its diameter is 2-3 meter . The furnace is made up of steel and lined with fire bricks. Coal is burnt in one side of the furnace. The hot gases are sent from one end to another end of the furnace. The highest temperature of the furnace is 1600 degree C . At this temperature following reactions take place:
CaCO3 ——–> CaO + CO2
3CaO + SiO2 ——–> 3CaO . SiO2
2CaO + SiO2 ———-> 2CaO . SiO2
3CaO + Al2O3 ———> 3CaO . Al2O3
The mixture obtained from furnace contains tri calcium silicate, di calcium silicate, tri calcium aluminate & tetra calcium alumino ferrite. This mixture is called cement clinker. It is ground and mixed with gypsum and in this way cement is manufactured. Addition of gypsum decreases the rate of setting of cement.
source : tutor vista.com
Note:
a) Cement containing excess amount of lime, cracks during setting while cement containing less amount of lime is weak in strength.
b) Cement with excess of silica is slow in setting
c) Cement having excess of alumina is quick in setting.
Mortar:
It is the mixture of cement and sand in the ratio of 3:1 with water. It is used in the construction of brick walls and covering the surface with cement(plastering of wall).
Concrete:
It is the mixture of cement , sand & grid ( small stone pieces generally called gitti) and water. It is very hard and used in making beam, floor etc.
Reinforced concrete :
Concrete ( cement, sand, grid & water) is filled in & around the skeleton of iron rod. This structure is called reinforced concrete . It is used in the construction of roads, bridges, roof, beam, pillars etc.
