Fine sand should consist of natural sand or crushed stone sand. It should be hard, durable, clean and be free from organic matter etc.Fine Sand should not contain any appreciable amount of clay balls and harmful impurities such as alkalis, salts, coal, decayed vegetation etc. The silt contents should not exceed 4%.
Classification of Sand
Classification of sand is given below.
1. Fine sand = 0.075 to O.425 MM
2. Medium sand = 0.425 to 2 MM
3. Coarse Sand = 2.0 to 4.75 MM
Various Types of Sand
There are following three types of sand.
1. Pit Sand
2. River Sand
3. Sea Sand
Pit Sand (Coarse Sand or Badarpur)
Pit sand is obtained by forming pits into soil from ‘Quarries’. It consists of sharp angular grains which are free from salts. It is coarse sand which is usually used in concreting and has reddish yellow color normally.
This sand is obtained from banks or beds of rivers. River sand is fine and consists of fine rounded grains. The color of river sand is almost white and Grayish. River sand is usually available in clean condition and is used for plastering.
This sand is obtained from sea shores. It has fine rounded grains and light brown color. Sea sand contains salts which attract moisture from atmosphere. Such absorption causes dampness and disintegration of work. Sea sand also retards setting action of cement. Due to these reasons, sea sand is generally avoided for engineering purposes. It is used only as a local material for nonstructural purposes.
Sand for Construction Works
Different construction works require different standards of sand for construction.
• Brick Works: finest modulus of fine sand should be 1.2 to 1.5 and silt contents should not be more than 4%.
• Plastering Works: finest modulus of fine sand should not be less than 1.5 and silt contents should not be more than 4%.
• Concreting Works: coarse sand should be used with finest modulus 2.5 to 3.5 and silt contents should not be more than 4%.
- If the above quality of sand is not available due to any reason, the blending of sand should be done by adding more coarse sand to achieve the required finest modulus.
- Washed sand should be used at site for getting more strength in construction work.
Bulking of Sand
Due to moisture in each particle of sand, sand gets a coating of water due to surface tension which keeps the particles apart. This causes an increment in volume of sand known as Bulking.