CONTENTS
Lime is an important binding material used in building construction. Lime has been used as the material of construction from ancient time. When it is mixed with sand it provides lime mortar and when mixed with sand and coarse aggregate, it forms lime concrete.
TYPES OF LIME AND THEIR PROPERTIES
[1] FAT LIME
Fat lime composed of 95% of calcium oxide. When water is added, it slakes vigorously and its volume increases to 2 to 2½ times. It is white in colour.
PROPERTIES OF FAT LIME
[1] It hardens slowly.
[2] It has high degree of plasticity.
[3] It sets slowly in the presence of air.
[4] Fat Lime is white in colour.
[5] It slakes vigorously.
[2] HYDRAULIC LIME
The Hydraulic lime contain clay and ferrous oxide. The percentage of clay present in this lime will determine it’s properties and what it can be used for.
TYPES OF HYDRAULIC LIME
[1] Feebly hydraulic lime (5 to 10% clay content)
[2] Moderately hydraulic lime (11 to 20% clay content)
[3] Eminently hydraulic lime (21 to 30% clay content)
PROPERTIES OF HYDRAULIC LIME
[1] Hydraulic Lime Sets under water
[2] The Colour of the hydraulic lime is not perfectly white
[3] Hydraulic Lime Forms a thin paste with water and do not dissolve in water.
[4] Its binding property improves if its fine powder is mixed with sand and kept in the form of heap for a week, before using.
[3] POOR LIME
Poor Lime contains more than 30% clay. Its colour is muddy. It has poor binding property.
The mortar made with poor lime is used for inferior works.
CLASSIFICATION OF LIME
[1] CLASS A LIME
It is predominently hydraulic lime. It is normally supplied as hydrated lime and is commonly used for structural works.
[2] CLASS B LIME
It contains both hydraulic lime and fat lime. It is supplied as hydrated lime or as quick lime. It is used for making mortar for masonry works.
[3] CLASS C LIME
It is predominantly fat lime, supplied both as quick lime and fat lime. It is used for finishing coat in plastering and for white washing.
[4] CLASS D LIME
This lime contains large quantity of magnesium oxide and is similar to fat lime. This is also commonly used for white washing and for finishing coat in plastering.
[5] CLASS E LIME
It is an impure lime stone, known as kankar. It is available in modular and block form. It is supplied as hydrated lime. It is commonly used for masonry mortar.
USES OF LIME
The following are the uses of lime in civil works:
[1] Lime is used for white washing.
[2] Lime is used for making mortar for masonry works and plastering.
[3] To produce lime sand bricks.
[4] For soil stabilization.
[5] As a refractory material for lining open hearth furnaces.
[6] Lime is used for making cement.
TESTS ON LIMESTONE
The following practical tests are made on limestones to determine their suitability:
[1] PHYSICAL TEST
Pure limestone is white in colour. Hydraulic limestones are bluish grey, brown or are having dark colours. The hydraulic lime gives out earthy smell. They are having clayey taste. The presence of lumps give indication of quick lime and unburnt lime stones.
[2] HEAT TEST
A piece of dry stone weighing W1 is heated in an open fire for few hours. If weight of sample after cooling is W2, the loss of weight is W2 – W1. The loss of weight indicates the amount of carbon dioxide. From this the amount of calcium carbonate in limestone can be worked out.
[3] CHEMICAL TEST
A teaspoon full of lime is placed in a test tube and dilute hydrochloric acid is poured in it. The content is stirred and the test tube is kept in the stand for 24 hours. Vigorous effervescence and less residue indicates pure limestone. If effervescence is less and residue is more it indicates impure limestone.
If thick gel is formed and after test tube is held upside down it is possible to identify class of lime as indicated below:
- Class A lime, if gel do not flow.
- Class B lime, if gel tends to flow down
- Class C lime, if there is no gel formation.
[4] BALL TEST
This test is conducted to identify whether the lime belongs to class C or to class B. By adding sufficient water about 40 mm size lime balls are made and they are left undisturbed for six hours. Then the balls are placed in a basin of water. If within minutes slow expansion and slow disintegration starts it indicates class C lime. If there is little or no expansion, but only cracks appear it belongs to class B lime.
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