The Bureau of Indian Standards (IS: 1624–1974) provides a number of field tests for building lime, which can be easily conducted in the field. They are discussed below.
Visual Examination
Class C lime is identified by its pure white colour.
Hydrochloric Acid Test
Hydrochloric acid of 50% strength is added to powdered lime kept in a test tube till effervescence ceases. Generally, a teaspoonful of powdered lime of about 10 cc is required. It is kept for 24 hours. The bubbling reaction indicates the presence of lime. The volume of insoluble residue signifies unwanted inert material.
Class A lime shows the formation of good thick gel after 24 hours of letting the mixture stand. Class B lime shows the formation of gel, whereas no gel is formed in the case of Class C lime.
Ball Test
Sufficient water is added to lime and a ball of the size of an egg is made. It is stored for 6 hours and then placed in a basin of water.
If it shows expansion and disintegration in a few minutes, it signifies Class C lime. If the expansion is less with a number of cracks, it can be categorised as Class B lime. Class A lime will not show any adverse effects.
Impurity Test
A known weight of lime is mixed with water in a beaker and the solution is decanted. The residue is dried in the sun for 8 hours, cooled and weighed. Based on the percentage of residue, the quality of lime is decided. Residue of less than 10% indicates that the lime is good, 10–20% indicates fair and above 20% indicates poor.
Plasticity Test
A small quantity of lime is mixed with water and left overnight. The so-formed material is spread like butter on a blotting paper with a knife to test its plasticity. Good lime indicates high plasticity.
Workability Test
An 1:3 lime mortar is made with adequate water. The mortar is thrown on a brick wall by a trovel. The sticking quality is examined. If it sticks well, then its workability is good.
POZZOLANIC MATERIALS
Pozzolanic materials are siliceous and aluminous materials, which do not possess any cementitious properties but form cementitious compounds by reacting with lime in the presence of water. It is volcanic ash containing about 80% clay.
The use of pozzolanic materials provides the following improvements:
- Improves workability
- Lowers the heat of hydration
- Assists in early setting and hardening of the mortar
- Reduces shrinkage
- Improves hydraulic properties and resistance to chemical attacks.
Naturally available pozzolanic materials are clay and shale, diatomaceous earth, volcanic tuffs and pumicites. Artificially available pozzolanic materials are fly ash, blast furnace slag, silica fume, rice husk ash, metakaoline and surkhi.
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