Lime as Building Material 

Before the invention of portland cement, lime was used us the chief cementing material in the construction industry.

Today, the use of lime has become very limited and is sometimes used in places where lime is locally available and the availability of portland cement is scarce.

Lime is not available in nature in its free state, as it reacts with CO₂ to form calcium carbonate.

Lime also has some unique applications such as its addition to cement mortar increases the workability and delays the setting time, thus the mortar can be used for longer periods after mixing.

Manufacturing of Lime 

The raw material for the manufacturing of Lime is Limestone (CaCO₃).

Lime is obtained from limestone through a process known as calcination.

Other raw materials from which Lime can be manufactured are kankars, shell, corals and chalk.

The heating of limestone to a temperature of about 900°c in the presence of air to obtain lime is known as calcination.

The quick lime produced by calcination is very unstable and if left exposed it will react with carbon dioxide present in the atmosphere and revert back to calcium carbonate.

To avoid this, stabilization of quick lime has to be done, which is achieved by sprinkling water over quick lime, known as slaking.

Slaking of lime, which is an exothermic reaction, converts the quick lime to calcium hydroxide (Hydrated lime), which is in powdered form.

The slaked lime so produced is sieved through IS sieve 3.5 and is used for various construction purposes like making mortar, lime putty, white washing, etc.

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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.

Storage of Lime on Site

Basically lime reacts with moisture present in the atmosphere and even on the ground surface. Hence proper care must be taken while storing lime on site.

To avoid the air slaking of lime, they should be stored in compact heaps and in insulated spaces.

It should be kept under covered and closed space when in the form of hydrated lime and they should be used within a week when in the form of quick lime.