Fine aggregate/ coarse sand consists of natural sand, crushed stone sand or crushed gravel stone dust. It should be hard, durable chemically inert, clean and free from organic matter, not containing any appreciable amount of clay balls or pellets and other harmful impurities i. e. alkaline, salt, mica, decayed vegetation, lumps etc.
It should be passed through I. S. Sieve 4.75 MM. It should have the finest modulus 2.50 to 3.50 and silt contents should not be more than 4%. Coarse sand should be either river sand or pit sand; or combination of the two. It should be obtained from Badarpur Sand or Stone dust obtained by crushing hard stones or gravel. It should also be obtained from river bed such as Tajewala , Dadupur sand.
In general the sand particle should be coarser and have minimum silt contents. The silt contents should not be more than 4%.
The quality of the sand has more impact on the strength of the structure inspite of the quantity of the cement used.
1) If there is more silt in coarse sand, the strength of cement mortar is reduced from 1 % to 30%.
2) If you take best quality coarse sand, it will give maximum strength.
Quality of Coarse Sand
Actual specification for the quality of coarse sand can be obtained by laboratory test but in general we can judge the quality of coarse sand in the field through the following ways.
1. Observe whether there are any lumps of earth or clay balls, grass and decayed vegetation etc. in coarse sand to check silt contents.
2. Take some samples of coarse sand in hand and observe
The particles of sand should be coarser.
Silt contents should be less
3. Take some sand in hand and drop it down
One can simply check the quality of sand by taking some sand in the hand and then dropping it down. If some finest material sticks with hand, the sand has some silt contents and finer sand.
4. Check silts contents with the help of water
Take empty glass and put some sand and water in the glass and stir it well. After some time the silt layer will be framed between sand and water which shows the quantity of the silt contents present in the sand.
Grading of Fine Aggregate
The following table shows grading of Fine Aggregate.
| S. No.
|| IS Sieve Designation
|| % Passing by Weight |
|| 10 mm
|| 4.75 mm
|| 95 - 100|
|| 2.36 mm
|| 1.18 mm
|| 55 - 90|
|| 600 micron
|| 35 - 60|
|| 300 micron
|| 8 - 30|
|| 150 micron
|| 0 - 10|