CLASSIFICATION AND CHARACTERISTICS OF LIME
Lime has been used as a cementing material since the ancient times in India and abroad. Ancient Egyptians and Romans used this material for various constructional processes. Even in India, various engineering structures like palaces, bridges, temples etc were constructed with lime mortar and still are in shape.After the invention of cement in 1824 lime has been replaced by the cement to a large extent, however it is still used at certain places, like for the repairing of the structures which were originally built with the lime mortar and at the places where lime is freely available and cement has its acute shortage.
Characteristics of Lime
- Lime has good plasticity and has high workability.
- It has good cementitious properties and is suitable for masonry works.
- If stiffens easily and has high resistance to moisture. Because of its high water retentively, shrinkage on drying is small compared to cement.
Classification of Lime
The properties of a Lime depends on the percentage of impurities present in it. Generally, lime is classified into three types.
Rich or Fat Lime :
- This lime is produced by the calcination of nearly purest form of limestone, chalk, marble, etc.
- Its color is perfectly white.
- It should have impurities of clay less than 5 percent.
- It slakes vigorously and volume becomes 2 to 3 times.
- Since the slaking process is vigorous for this lime, care must be taken to avoid any fire hazards.
- It sets slowly in the presence of air, thus it is not suitable for thick wall joints or in wet conditions.
- Fat lime is extensively used in the manufacturing of cement, metallurgical industry, white washing, etc.
Hydraulic Lime :
- This lime is produced by the moderate burning of limestone which contains small proportions of clay, iron oxide and other impurities.
- It has impurities in the range of 5 to 30 percent.
- The increase in the percentage of clay makes the slaking difficult and increases its hydraulic property.
- Care must be taken during the slaking of this lime, as any excess addition of water will cause the lime to harden.
- Depending on the percentage of clay present, it is further classified into feebly, moderately and eminently hydraulic lime.
Poor Lime :
- This lime is also known as lean lime or impure lime.
- It contains clay impurities more than 30%.
- It slakes very slowly and forms a thin paste when mixed with water.
- It is muddy white in color.
- It sets or hardens very slowly and has poor binding properties.
- This lime is used for the construction of interior structures and at places where the availability of good lime is less.