Physical and chemical tests are conducted on limestone to determine their suitability.
Physical Tests
Physical tests are based on the texture, appearance, colour and odour of limestone. Limestone showing amorphous textures are suitable for making lime.
Chalk and fat lime deposits are white or whitish-brown or grey in colour. Magnesium limestone is distinguished from its heaviness and hardness.
Limestone with white, bluish-grey, yellow or brown colours are suitable for producing hydraulic lime. These limestones show a compact texture with an irregular dull fracture. A freshly fractured surface of such limestone has an earthy smell and is clayey in taste.
Chemical Tests
1. Heat Test
A piece of dry limestone is weighed and heated on an open fire for a few hours. The limestone disintegrates emitting CO2. Due to the removal of CO2 from the sample, it loses weight. The sample is weighed again. The loss of weight indicates the amount of CO2. From this, the percentage of calcium carbonate present in the limestone is determined.
2. Acid Test
The purpose of this test to classify the limestone and to determine the percentage content of calcium carbonate.
A teaspoon of powdered lime is placed in a test tube, and dilute hydrochloric acid is added. The contents are stirred with a glass rod and set aside for 24 hours.
Abundant effervescence indicates a high percentage of calcium carbonate. On the other hand, the formation of residue signifies that the limestone is impure or hydraulic. The absence of formation of gel signifies fat lime.
The formation of a thick gel shows primarily the presence of hydraulic lime, and gel of moderate thickness signifies feebly hydraulic lime.
3. Slaking Test
Quick lime in combination with water hydrates, and the process is known as slaking. A lot of heat is generated during slaking, which indicates that the percentage of calcium content is high in the limestone. In the case of hydraulic lime, the slaking action is very slow.
The Bureau of Indian Standards (IS: 6932–1973) specifies 10 laboratory tests for lime (Methods of Test for Building Lime – Parts 1 to 11). The reader may refer to the codes for details.
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