Classification of Lime as a Building Material for use in Construction
Neenu S K
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The classification of lime as a building materials for use in construction works based on IS 712-1973 is classified to different classes based on their applications in construction.
Other than the mentioned lime under specified classes, there is carbide lime. The manufacture of acetylene gives the by-product carbide lime. Under special consideration, it can be used for special plaster works. This is used only if it is available in fresh condition.
If it is available in a semi-solid form, it is not recommended for any work. This is because it dries up quickly. The lime that contains clay greater that 30% is considered as poor lime.
Classification of Lime as a Building Material for use in Construction
Following table shows the classification of lime and its name for use in various construction works:
Table.1. Classification of Lime as a Building Material for use in Construction as per IS 712-1973
CLASS
LIME NAME
Class A
Eminently Hydraulic Lime
Class B
Semi - Hydraulic Lime
Class C
Fat Lime
Class D
Magnesium or dolomite lime
Class E
Kankar Lime
Class F
Siliceous Dolomite Lime
The Class A lime are the hydraulic lime, that undergoes setting under the action of water. These are used for the construction of structures like arches and domes.
Class B is semi-hydraulic in nature. They are limited to small area work, like in masonry constructions.
Class C are called as fat lime. Another name for the same is quick lime or white lime or non-hydraulic lime. These are used for works like whitewashing, as a final coat for plastering etc. It is also used in the making of masonry mortar with the help of an additional pozzolanic material.
Class D is categorized for lime that is of magnesia or dolomite origin. For finishing works of plastering and whitewashing, the class D lime can be used
Kankar lime is the lime that is categorized under the class E. This lime is produced by the burning of lime nodules that are mainly found in the black soils, that constitutes silica. This forms to be hydraulic in nature. The main application of Kankar lime is in masonry mortar.
The siliceous dolomite lime is grouped under the class F lime. This is mainly used in the finishing coat of plaster or for its undercoat.
The compressive strength gained by the mortar mix of lime and cement, for different classes are shown in table 2.
Table.2: Compressive Strength of Lime Mortar Mixes and Cement Mortar Mixes
Preparation of Slaked Lime
The procedure behind the making of slaked lime is described in the following steps:
The required quantity of fat lime or quicklime is placed over a platform which is wooden or masonry, free of moisture. The quicklime is produced by the burning of limestone and shells.
Water is then sprinkled over this heap of quick lime, till it gets reduced to powder form. During the addition water, thorough mixing is done along with this, until no more water is required to completely reduce the quicklime to the powdered form.
The final mixture is allowed to pass through the sieve of 3.35mm dimension. The residue is rejected. The final product is called the slaked lime.
Preparation of Lime Putty
Before the use of quicklime in lime mortar, it is made into lime putty. The procedure of lime putty preparation is explained in the following procedures:
Initially, two tanks are made of 50 and 80 cm deep (Tank 1 and Tank 2 respectively). The former tank is constructed at a higher level compared to the latter, to ensure proper flow of fluid from tank 1 to tank 2.
Initially, the tank 1 is filled with water to its half. Quick lime is then added to this, till the half depth of the tank 1 is filled. It is kept in mind to add lime to the water and not water to lime.
Proper stirring is carried out, keeping in mind that no exposure to the air above the water level is carried out. The mixing will be continued for few minutes (around 5 minutes), till the moment the boiling ends and the whole mixture starts to thicken.
The mixture is den allowed to flow to the tank 2, located at the lower height. For this to happen with ease, more water can be added.
The tank 2 takes this mixture for a minimum time of 72 hours. The lower tank (tank 2) is made up of dry brick masonry, whose joints are filled with sand alone. This would facilitate the absorption of water from the slurry. This is the way, how the excess water is removed and lime putty is obtained in the paste form.
If the exposure to the atmosphere is avoided, it can be stored for a period of say 2 weeks.
The addition of water in a gradual means will make the hydraulic lime slaked. When compared to quicklime, the hydraulic lime requires lesser water.
The fat quick lime is said to slake by an amount of twice, in the powder form and by one and a half parts of paste. The hydraulic lime slakes by an amount of one and half in the powder form and by the same quantity in the paste form.
Storage of Lime as a Building Material
If it is necessary to store quick lime for a longer period, it is advised to store it in airtight vessels or in the form of large heaps, to ensure that no air is coming in reaction with the mixture.
The package of slaked lime can be done for three to four months with the help of gunny bags, craft papers or polyethylene bags etc. This after the package must be stored in a dried place.
The area must be weatherproof. The floor must be watertight and impervious. In construction requirement, there are certain specifications demanded like, the lime slaked should be having a package period of one week or more than four, for their application.
