Bulking of Sand

AIM:

To Determine the Bulking of Fine Aggregates / Sand

THEORY:

Moist or wet sand occupies larger volume if loosely filled in, than dry sand. Due to moisture, a thin-film of water forms around sand grain which results in increase of volume. This effect causes increase in volume (if loosely filled in) due to moisture content is called “Bulking of sand”.
The bulking of sand is largely depends on

1. Grain size: Smaller the grain size, larger will be bulking effect and vice versa.
2. Moisture content: 5-8 % moisture can result in 20-35 % increase in volume

Bulking increases with the increase in moisture content up to a certain limit, beyond that limit the further increase in moisture content results in decrease in volume.

Effect of Bulking of Sand in Concrete Production:

While batching of aggregates, if weight batching is adopted which is precise and preferred method of batching of aggregate, no effect is taken place due to bulking of sand. However, if batching is done by volume, then less sand than required as per mix design will be measured. This will result in disproportionate and non-uniform concrete mixes and may affect the compressive strength of concrete. Therefore it is essential to increase the volume of sand by the ‘percentage’ bulking.

APPARATUS:

1) Weighing Balance

2) Cylindrical measure of 250 ml

3) Metal tray

4) Water

5) Steel rule

PROCEDURE:

1. Take 250 gms of the aggregate.
2. Add 2% by weight of water and mix well.
3.  Transfer the sand sample into a 250 ml measuring cylinder and consolidate by shaking.
4.  Level the surface with steel rule and read the volume in ml.
5. Take out the whole quantity of sand and continue the experiment by adding 2% water more each time and note the corresponding volume of sand (Y2,Y3…..) until the dumped sand volume starts decreasing.
6. Beyond this point, add 4% more water each time until the sample become fully saturated.
7. A graph drawn with % of water content along X-axis and % of bulking along Y- axis and from the graph, pick out maximum % of bulking occurred, % of water content at maximum bulking.

OBSERVATIONS AND CALCULATIONS:

Weight of sample = _________grams

Height of dry sand h = _________mm

RESULT:

1. Maximum Percentage of Bulking = __________
2. Percentage of water content at maximum bulking = __________

CONCLUSION:

REVIEW QUESTIONS:

1. Draw the phase diagram for bulking of sand.
2. What is meant by bulking of sand?
3. Is it necessary to calculate percentage of bulking? If yes, why?
4. What is the effect of bulking of sand in concrete production?
5. Why the bulking percentage decrease after certain value?
6. What are the factors which influences bulking of sand?