BULKING OF SAND (Fine Aggregate):

The volume of the sand increases due to the presence of the moisture content and is termed as bulking.Fine sand bulks more as compared to coarse sand.Fine aggregate bulks as much as about 40 %.Remember, fine aggregates do not show any bulking when it is absolutely dry or completely saturated.

CAUSE OF BULKING:

A film around each particle is formed due to the moisture present in sand.These films of moisture exert a force,known as surface tension on each particle.Due to this surface tension each particle gets away from each other.So, there is no direct contact possible among the individual particles and this causes bulking of the volume.

Bulking of fine aggregate depends upon two factors:

1.Particle size of aggregates.
2.Percentage of moisture content.

Bulking increases with increasing moisture content to a certain extent and further increase increase in moisture content results in decrease in volume. When the fine agregate becomes fully saturated, it shows no bulking. The percentage of bulking is indirectly proportional to the size of particle.

Why to determine Percentage of bulking?

Due to bulking, the fine aggregate shows completely unrealistic volume. Therefore, it is absolutely necessary that condiseration must be given to the effect of bulking in proportioning the concrete  by volume. If the impact of bulking is not taken into account, due to the collision of volume batching, the resulting concrete is likely to be under-sanded and harsh. This will also affect the yield of concrete for a given cement content.

### 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)
As per IS2386-3 Bulking in Sand, Presence of 4% of moisture content in sand increases 25% of its volume is given in the table below:

 %of Moisture content Percentage  Bulking                 (by volume) 2% 15% 3% 20% 4% 25% 5% 30%

Bulking of Sand Formula:-

Lets us take an Observation:

The measured height of Sand (H1)= 250mm
and height of sand with water (H2)= 200 mm, so it follows

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.(see the table above)