What is a limestone? Types of limestone, testing performed on it, Properties and application of limestone

Introduction

Lime, an ancient material, has been important in different parts of human life, from building to farming. This blog will delve into lime's various aspects, including its types, testing procedures, unique characteristics, and extensive uses.

Close-up of gray limestone rocks with a text overlay reading "Limestone" against a gradient background. The image conveys a natural, textured feel.

Defination of limestone

Limestone, a white alkaline substance primarily composed of calcium oxide, forms when heat decomposes materials containing calcium carbonate. As a result, it becomes highly valued for its alkalinity and its ability to produce calcium hydroxide when mixed with water. Therefore, builders, farmers, and industries consistently use it in various applications. Specifically, lime plays a crucial role in making mortar, stabilizing soil, and treating water effectively.

Lime

Lime serves as an important binding material in building construction. Builders have used it as a construction material since ancient times. When mixed with sand, it forms lime mortar, and when combined with sand and coarse aggregate, it produces lime concrete.

Types of Limestone and their Properties

The limes are classified as fat lime, hydraulic lime and poor lime:

(i) Fat lime: This material contains 95% calcium oxide. When you add water to it, it slakes vigorously, increasing its volume by 2 to 2½ times. It appears white in color. Its properties are:

hardens slowly
has high degree of plasticity
sets slowly in the presence of air
white in colour
slakes vigorously

(ii) Hydraulic lime: Clay and ferrous oxide make up its composition. Based on the percentage of clay present, experts classify hydraulic lime into the following three types:

Feebly hydraulic lime (5 to 10% clay content)
Moderately hydraulic lime (11 to 20% clay content)
Eminently hydraulic lime (21 to 30% clay content)

The properties of hydraulic limes are:

Sets under water
Colour is not perfectly white
Forms a thin paste with water and do not dissolve in water.
Mixing its fine powder with sand and heaping the mixture for a week before use improves its binding property.

(iii) Poor lime: This lime contains more than 30% clay and appears muddy in color. It shows poor binding properties. Builders use the mortar made from this lime for inferior construction works.

IS 712-1973 classifies lime as class A, B, C, D and E.

Class A Lime: Manufacturers predominantly produce hydraulic lime, supply it as hydrated lime, and use it commonly for structural works.
Class B Lime: It combines both hydraulic lime and fat lime. Suppliers provide it as either hydrated lime or quick lime. Builders use it to make mortar for masonry works.
Class C Lime: It consists predominantly of fat lime and comes as both quick lime and fat lime. Builders use it for the finishing coat in plastering and for whitewashing.
Class D Lime: This lime contains a large quantity of magnesium oxide and resembles fat lime. People commonly use it for whitewashing and applying the finishing coat in plastering.
Class E Lime: People know this impure limestone as kankar. It comes in modular and block forms. Suppliers provide it as hydrated lime, and builders commonly use it for masonry mortar.

Tests on Limestone

Engineers perform the following practical tests on limestones to determine their suitability:

Physical tests
Heat test
Chemical test
Ball test.

(i) Physical Test: Pure limestone is white in colour. Hydraulic limestones are bluish grey, brown or are having dark colours. The hydraulic lime gives out earthy smell. They are having clayey taste. The presence of lumps give indication of quick lime and unburnt lime stones.

(ii) Heat Test: A piece of dry stone weighing `W_2` is heated in an open fire for few hours. If weight of sample after cooling is `W_2`, the loss of weight is `W_2-W_1`. The loss of weight indicates the amount of carbon dioxide. From this the amount of calcium carbonate in limestone can be worked out.

(iii) Chemical Test: A teaspoon full of lime is placed in a test tube and dilute hydrochloric acid is poured in it. The content is stirred and the test tube is kept in the stand for 24 hours. Vigourous effervescence and less residue indicates pure limestone. If effervescence is less and residue is more it indicates impure limestone.

If thick gel is formed and after test tube is held upside down it is possible to identify class of lime as indicated below:

Class A lime, if gel do not flow.
Class B lime, if gel tends to flow down.
Class C lime, if there is no gel formation.

(iv) Ball Test: This test is conducted to identify whether the lime belongs to class C or to class B. By adding sufficient water about 40 mm size lime balls are made and they are left undisturbed for six hours. Then the balls are placed in a basin of water. If within minutes slow expansion and slow disintegration starts it indicates class C lime. If there is little or no expansion, but only cracks appear it belongs to class B lime.

Uses of Lime

The following are the uses of lime in civil works:

For white washing.
For making mortar for masonry works and plastering.
To produce lime sand bricks.
For soil stabilization.
As a refractory material for lining open hearth furnaces.
For making cement.

Conclusion

To sum up, limestone is a well-established wonder that effortlessly integrates into our daily lives. Its different types, thorough evaluation, special characteristics, and diverse uses highlight lime's flexibility and necessity in today's society. While we search for eco-friendly and effective options, lime remains a fundamental part in building, manufacturing, farming, and safeguarding our past.