Tests on Limestone

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In the construction industry, Lime is one of the best binding materials available and is used widely for different purposes such as mortar making, plastering, whitewashing, etc. Lime obtained by the calcination of limestone, which occurs naturally. Different tests are carried out on limestone to check its properties and to know the proportions of ingredients in it. The tests with the procedure are explained in this article.

Tests on Limestone

Following four tests are conducted on limestone/powdered limestone.

1. Physical test
2. Heat Test
3. Acid Test
4. Ball Test

1. Physical test

The physical properties of lime can be estimated by its color, smell, texture, etc. White color indicates pure limestone. The bluish-grey, brown, dark color indicates hydraulic limestone. Hydraulic limestone tastes like clay and produces an earthy smell. If limestone is glittering or shining, then it indicates the presence of free salts in it. Similarly, the presence of bulges or bumps indicates it as quick lime.

2. Heat Test

Heat test is performed to find the amount of calcium oxide (lime) present in the limestone. In this test, a sample of dry limestone is weighed and it is heated for four hours in an open fire. During heating, carbon dioxide present in the limestone evaporates and weight reduces. After heating, the sample is weighed for loss of weight is recorded. Form this data, Amount of calcium oxide content present is determined.

3. Acid Test

The acid test is used to determine the amount of calcium carbonate and type of lime present in the limestone. The procedure of acid test is as follows.

• A teaspoon of powdered lime is taken in the test tube and 10 ml of dilute hydrochloric acid is added to it.
• Substances are stirred thoroughly and kept the mix in a safe place for 24 hours.
• After 24 hours, observe the mix. If there is a formation of high effervescence and less residue left at the bottom of the tube then it indicates a high amount of calcium carbonate which represents pure limestone.
• If the formation of effervescence is less and more residue is left at the bottom of the test tube then it indicates less amount of calcium carbonate in it and is treated as impure or hydraulic limestone.
• To classify the lime present in the limestone, perform another test continuation to the above test.
• In this step, just invert the above test tube with its upside-down if the gel formed above the residue is not moving even when the test tube is inverted then it is designated as class A lime.
• If the gel formed tends to flow when the test tube is inverted then it is designated as Class B lime.
• If there is no gel formation, then it is designated as class C lime.
• Following table distinguishes class A, B and C type limes.

Lime Class	Lime Type	Lime Percentage	Uses
Class A	Eminently Hydraulic Lime	60 – 70	Mortar for foundation works, damp place works, etc.
Class B	Semi Hydraulic Lime	70-75	Mortar for masonry, flooring, etc.
Class C	Non-Hydraulic Lime / Fat lime	93-95	Plastering, white washing, etc.

4. Ball Test

The test procedure of ball test contains the following steps.

• Powdered lime is taken and water is added to it until stiff consistency is achieved.
• Using this stiff mixture, balls of 40 mm size are prepared.
• These balls are left undisturbed for six hours.
• After six hours, the balls are immersed in a water basin.
• If lime balls are expanded and disintegrated in the water within minutes then it indicates the presence of class C lime.
• If there is no expansion or very little expansion and numerous cracks on balls then it indicates the presence of class B lime.