INTRODUCTION

There are several naturally available civil engineering materials or materials directly produced from natural materials. Among them are binding materials, which play a major role. Lime, cement and bitumen are important for civil engineers.

Binding materials may be of air binding, hydraulic binding and autoclave binding.

Air binding materials, also known as air-setting binding substances, pass into a stone state in air, gain strength and then retain their mechanical properties. Lime, cement, gypsum, etc., are examples of air binding materials.

Hydraulic binding materials, also known as hydraulic-setting substances, pass into a stone stage in air and as well as in water, gain strength and then retain their mechanical properties. Hydraulic lime, cement, etc., are examples of hydraulic binding materials.

Autoclave binding materials, also known as autoclave-setting substances, set only when treated in autoclaves with saturated steam under pressure of 8–12 atmosphere and at a temperature between 170 and 200ºC. Lime–silica, sand, Portland cement, etc., are examples of autoclave binding materials.

5.2 CONSTITUENTS OF LIMESTONE

Lime is not freely available in nature but is obtained by burning naturally available materials such as:

1. Limestone found in limestone hills
2. Limestone boulders found in the bed of old rivers
3. Kankar found below ground and
4. Shells of sea animals.

Lime is more or less pure calcium carbonate. The main sources of obtaining lime are the stones which possess clay, soluble silica, magnesium carbonate, alkalis and metallic oxides, sulphates, iron compounds and carbonaceous matter.