BULKING OF SAND:-
Bulking in sand Occurs When dry sand interacts with the atmospheric moisture. Presence of moisture content forms a thin layer around sand particles. This layer generates the force which makes particles to move aside to each other. This results in the increase of the volume of sand.
Excessive presence of moisture content in the sand makes concrete to less durable and lose its strength. Remember, excessive presence of moisture content increase the workability of concrete but loses its strength.
As per IS2386-3 Bulking in Sand, Presence of 4% of moisture content in sand increases 25% of its volume.
|% of Moisture content||Percentage of Bulking with respect to volume|
The extent of sand bulking depends on the grading of sand. Finer Sand possesses more bulking than the medium and coarse sand. Thus, Bulking in the sand is high for fine sand and low for coarse sand. An increase of bulking in sand effects concrete mix and results in harsh behaviour while placing.
Moisture content less than 5% should be preferred for construction purposes.
In order to calculate the bulking of sand/ Percentage of moisture content in the sand, the moisture content of sand is further increased by adding some more water. Due to this, the sand particles pack close to each other and the Bulking of sand is gradually decreased. Therefore this helps in finding the actual volume of sand(dry sand). In simple words, the dry sand and fully saturated sand have the exact volume.
The percentage of bulking can be determined by following this method:-
1. Take a simple container and add 2/3 part of sand in it.
2. Measure the exact height of sand using the scale and note it down. (H1)
3. Now fill the container up to 2/3 part with water. (Same height of Sand)
4. Now add the measured sand to the container and wait for some time to settle down.
5. Now calculate the height of Sand in water. (H2)
Bulking of Sand Formula:-
For suppose the measured height of Sand is 200mm and height of sand with water = 160mm then
From the above table, it is clear that the Sample has 4% of Moisture content in it. Due to this 25% of the volume is increased in the sand.
For better understanding Refer the following video:-
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