Sand || Natural source of sand || Properties of good sand

Sand :-

It abundantly occurs in nature and is formed by the decomposition of rocks. Sand is an important building material. Sand particles consist of small grains of silica (SiO 2 ). It forms a major ingredient in concrete, lime mortar, cement mortar, etc. 

NATURAL SOURCES OF SAND :-

 Sand is formed by the weathering of rocks. Based on the natural sources from which sand is obtained, it is classified as follows: 

• Pit sand 
• River sand 
• Sea sand  

Pit sand :-

This sand is obtained by forming pits in soils. It is excavated from a depth of about 1-2 m from the ground level. This sand is found as deposits in soil and it consists of sharp angular grains, which are free from salts. It serves as an excellent material for mortar or concrete work. Pit sand must be made free from clay and other organic materials before it can be used in mortar. Also, the coating of oxide of iron over the sand grains should be removed. 

River sand :- 

This sand is widely used for all purposes. It is obtained from the banks or beds of rivers and it consists of fi ne rounded grains. The presence of fine rounded grains is due to mutual attrition under the action of water current. The river sand is available in clean conditions. The river sand is almost white in colour. 

Sea sand :-

Sea sand is obtained from the sea shores. It consists of fine rounded grains like the river sand. Sea sand is light brown in colour. Since the sea sand contains salts, it attracts moisture from the atmosphere. Such absorption causes dampness, efflorescence and disintegration of work. Sea sand increases the setting time of cement. Hence, it is the general rule to avoid use of sea sand for engineering purposes even though it is available in plenty. However, after removing the salts by washing, it can be used as a local material. 

Properties of good sand :-

Good sand should possess the following properties :-

• It should be clean and coarse. 
• It should be well graded, i.e., it should contain particles of various sizes in suitable proportions.
• It should be strong and durable. 
• It should be clean and free from coatings of clay and silt.  
• It should be chemically inert. 
• It should contain sharp, angular, coarse and durable grains. 
• It should not contain salts which attract moisture from the atmosphere. 
• It should be free from any organic or vegetable matter; usually 3-4 per cent clay is permitted.