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Natural Material (Lime)

What is lime? Or write short note on lime.
  • After process of calcinations of limestone moisture and carbon content are removed and remaining matter is called as lime.
  • Chemical composition of lime is CaO i.e. calcium oxide.
  • Process of calcinations
CaCO3                               CaO + CO2↑
  • The commercially calcium oxide is known as quick lime.
  • Limestone is always associated with silica, alumina, and iron oxide.
What are the properties of lime?
  1. It is white in colour.
  2. It has specific gravity 3.2.
  3. It have very high melting point i.e. 2575oC.
  4. Outstanding characteristics of lime are its ability of slaking.
What is slaking of lime?
The process of mixing of water in lime is called as slaking of lime.

Describe the process of slaking of lime.
For making mortar quick lime is mixed with water.
  • When 3 parts of quick lime is mixed with 1 part of water, it absorb the water and start to bursting and increasing volume. Also it produce hissing sound with increasing temperature. This increasing volume is finally converted into fine powder i.e. slaked lime.  CaO + H2O                  Ca(OH)2 + heat (15.2 kcal)
In short in this process following changes take place,
  1. Production of heat.
  2. Expansion in volume (2.5 times).
  3. Formation of hissing sound.
  4. Formation of fine powder i.e. slaked lime.
What are classifications of lime?
High calcium or fat lime: Compositions: It contains 90-95% CaO and less than 2% silica, alumina and iron oxide. Remaining part is magnesia, water and CO2.
Properties: 1. It slake very fast. Hence precaution is necessary.
       2. It is more expansive than other type of lime.
       3. It hard very slowly, hence it produce less hard mortar.
       4. It has high degree of plasticity.
       5. It is perfectly white in colour.
Uses:    1. It is used as mortar for masonry work.
             2. For white washing and plastering of wall.
             3. Water softening.
             4. In chemical and glass industries.
Poor lime or lean lime: Compositions: It contains 75% CaO and 25% clay, remainder being mostly silica, alumina, Fe2O3 and MgO.
Properties: 1. It is cheap.
                   2. It slakes slowly.
                   3. It makes poor mortar.
                   4. It is muddy white in colour.
Uses:    1. For white washing.
             2. It is used as mortar.

Hydraulic lime (Inferior grade natural cement):
Compositions: 70 to 80% CaO and 5 to 20% clay of silica and alumina and very small quantity of Fe2O3 and MgO.
Properties: 1. It has hydraulic properties.
                  2. It forms like hard mass like cement.
                  3. Capacity to set under water is very high.
Uses:    1. It used for under water construction.
             2. For preparation of mortar.
Dolomite or high magnesium lime: Compositions: it is mixture of CaCO3 and MgCO3. It is obtained by heating dolomite (CaCO3 and MgCO3). It contains 60-70% CaO, 30-40%MgO. And very small % of clay.
Properties: 1. It is too expansive.
                  2. It slakes very slowly.
                  3. It has low sand carrying capacity.
                  4. It produce strong mortar.
Uses:    1. It is used as a flux in metallurgy.
             2. For preparing special slags.
             3.  For repairing the basic refractories.
What is manufacturing process of lime?
The process of manufacturing of lime is carried out in three steps.
  1. Collection of lime stone: In this process raw material like limestone are collected at site. This should not be contains impurities more than 5%.
  2. Calcinations of lime stone: It means burning of lime stone. The fuel like wood, coal, charcoal is used for calcinations. The burning of lime stone can be done either clamps or kilns.
Following points are to be observed during calcinations of limestone:
  1. Colour of lime stone is bright red is indicate burning is complete.
  2. Burnt limestone should be taken out from the kiln as soon as CO­2removed.
  3. Avoid over or under burning of limestone.
  4. Heat limestone gradually, sudden heating is causes break stone into pieces.
  5. For sufficient burning, the quantity of fuel needed should be carefully decided.
  6. Maintain temperature at 8000C for proper burning.
  1. Sacking of burnt lime: The quick lime obtained by burning of limestone s are slaked by two method of slaking. 1. Slaking to past 2. Slaking to powder. Natural slaking is not used because it is very slow process.
What are the uses of lime in construction?
1.         It is used for final coat in internal plastering.
2.         It is commonly used in sun law or neeru finish work.
3.         It is used for making mortar.
4.         It is used for soil stabilization.
5.         Some time it is used for concreting.
6.         It is used as flux in metallurgy industries.
7.         It is used in manufacturing of glass.
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