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Lime

The Lime is calcium oxide (CaO) obtained by calcination of pure limestone (white chalk), kankar and other calcarious substances. It is not found in nature in the fress state.

  • It is used as a materix for concrete, for plastering walls, ceiling etc, 
  • For improving soil for agricultural purposes and
  • Used in the production of glass. 
  • It is also used as a flux in the manufacture of steel and
  • Used in  the manufacture of paints
Hydraulicity :- It is the property of lime by which sets in damp places, water or thick masonary walls where there is no circulation of air.
Calcination :- It is the process in which lime is heated to redness in contact with air.
Slaking :- Process of addition of water to quick lime is called slaking.

Constituents of lime 

  1. Clay :- Presence of clay in lime impacts hydraulicity to it and makes it insoluble in water. It should be in the range of 8 to 30%
  2. Soluble silicates:- Silicates in form of  calcium, magnesium and aluminium also impacts hydraulicity in lime.
  3. Magnesium carbonate:- Presence of magnesium carbonate in LIme allows it to slake and set slowly
  4. Sulphates:- Presence of sulphates in small quantity retards the process of slaking and increases the setting process of lime.

Classification of Lime

1) Quick lime 

It is the lime obtained after the calcination of of pure limestone. 
  • Have great affinity for water
  • Amorphous in nature
  • Have no affinity for carbonic acid
  • Also called caustic lime
  • Quick lime as it comes out from kilns is known as lump lime

2) Slaked lime or hydrated lime 

It is the lime formed by the absorption of water by quick lime. The process of chemical combination of quick lime with required quantity of water is known as slaking.
  • Rise of temperature accelerated the slaking process
  • Can be carried out speedily by steam under pressure in closed drums
Slaked lime should be used as fresh as possible because it absorbs carbonic acid from atmosphere as below:
  • Slaked lime shouldn't be stored in damp places.
NOTE:- Presence of siliceous matter in lime imparts hydraulicity to lime

3) Fat lime/High calcium lime/ Pure lime/ Rich lime/ white lime

  • It is the lime which has high calcium oxide (about 95%) and can set and become hard only in the presence of carbon dioxide from atmoshphere.
  • This type of lime is perfectly white in colour.
  • It has high plasticity.
  • It slakes rapidly with considerable evolution of heat and its volume increases two or three times of its original volume during slaking.
  • It takes very long time to develop adequate strength.
  • It is commonly used for white washing and plastering of walls.

4) Hydraulic lime / Water lime

It is the lime which has small quantities of silica, alumina and iron oxide, which are in chemical combinations with calcium oxide. It can set and become hard even in the absence of carbon dioxide and can set under water.
  • Consist of impurities like clay and some amount of ferrous oxide.
  • With increase of clay content slaking time also increases
  • With increase of clay content setting time and solubility in water decreases.
  • Strength is more than fat lime due to clay content.
The hydraulic lime depending upon the percentage of clayey impurities in the form of silica, alumina and iron oxide are classified into the following three groups:
  • a) Feebly hydraulic lime - 5 to 10%
  • b) Moderately hydraulic lime - 11 to 30%
  • c) Eminently hydraulic lime - 21 to 30%

5) Poor lime / lean lime

It is the lime which contains more than 30% of clayey impurities in the form of silica, alumina and iron oxide.
  • It sets very slowly
  • It has poor binding properties and its colour is muddy white.
  • Since the mortar made from this type of lime is of poor quality, therefore it is used for inferior type of work.

Uses of Lime

  1. It is used for finishing activites like plastering or white washing.
  2. It is used for masonary works.
  3. It is used for stabilization of soil
  4. It is used for manufacturing of glass for reducing the temperature.
  5. It acts as a flux in metallurgical operations.

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