Building Material – Lime

Lime :

Lime is an important cementing material used in engineering construction. A cementing material may be defined as that material which has the capacity of holding structural units (like bricks, stones, aggregate) together with sufficient strength.

LIME in its simplest form is an oxide of calcium, CaO. It has been used since ancient times in the construction of ordinary buildings and also massive monuments, palaces and forts.

In the present time, lime can be used as reliable and economical cementing material where portland cement is either costly or is not easily available as in hilly regions and remote villages.

Classification :

LIME is available in the market in three main types which are named on the basis of its composition:

Quicklime, hydrated lime and hydraulic lime.

A) Quick Lime / Fat Lime :

It is also called fat lime, rich lime or pure lime. In it CaO content is always greater than 93 percent by weight remaining being MgO and very little clay .

Quicklime is an amorphous (shapeless) white , material which is highly caustic in character. It has a very high affinity for water and carbon dioxide. It will absorb the same quickly even from atmosphere converting itself to a carbonate of calcium, as per following reactions

                                     CaO +Co2 = CaCO3

                                      CaO + H2O =Ca(OH)2

                      Ca(OH)2 + CO2 = CaCO3 + H2O

1)It hardens very slowly.

2)It has high degree of plasticity.

3) Its colour is perfectly White.

4) It sets slowly in presence of Air.

5) It is soluble in water which is changed frequently.

Uses – White washing , plastering , Lime mortar can be used for thin joints of brick work & stone works.

B) Hydrated Lime :

It is that lime to which sufficient quantity of water has already been added at the manufacturing stage to hydrate (slake) it completely.

In composition hydrated lime is Ca(OH)2.in structure. It may be a fine powder.

It comes in ready to use form compared to fat- lime that has to be hydrated or slaked before using. Lime can also be converted to hydrated form at the place of construction. The method is then called slaking of lime.

C) Hydraulic Lime :

It is different in chemical composition form fat lime in that it contains a definite amount of clay in addition to CaO.

The clay content in hydraulic limes may range form 10-30 percent by weight. This clay plus lime composition gives the hydraulic lime a property of hydraulicity.

• Which may be defined as “the capacity to set and harden even under water and in the absence of air as between very thick walls.”

         The hydraulic lime is further classified into three sub-types on the basis of hydraulicity (which is actually related to the clay content ) of the lime.

Divided into following three type :

1)Feebly Hydraulic Lime :

Clay content 5 to 10% , Slakes after few minutes , Sets in water in 3 weeks or so,Feeble.

Uses : The mortar produced by this lime is reasonably strong. Ordinary Masonry Work

2) Moderately Hydraulic Lime :

Clay content 11 to 20% , Slakes after one hour or two hours , Sets in water in a weeks or so,Moderate.

Uses : The mortar produced by this lime is reasonably strong. Superior Masonry Work.

3) Eminently Hydraulic Lime :

Clay content 21 to 30% , Slakes with difficulty , sets in water in a day or so, Eminent.

Uses : The mortar produced by this lime is similar the ordinary cement , It can be used for damp places.

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