When water is added to sand, by the absorption effect, a thin film of water is formed around the sand particles. The film exerts surface tension on particles making them move apart. This leads to increase in volume because there is no direct contact between particles.
For a moisture content percentage of 5 to 8 there will be an increase in volume up to 20 to 40 percent depending upon the sand quality. If the sand is finer there will be greater increase in volume. This is known as bulking of sand.
Test for determining sand bulking
The percentage of bulking of sand can be easily calculated by following this field method.
With the increase of moisture initially the volume of sand increases, but after certain time further increase in moisture results in decrease of volume.
When moisture content is 5 -10% the volume increases 20 – 40%.
Moisture content less than 5% should be preferred for construction purpose. At about 6 – 10%, the film starts breaking and volume reduces.
It has been found that 4% moisture content (By weight) of dry sand may increase its volume up to 25 -30% depending upon the grading of sand. Finer sand results in extreme bulking.
This phenomenon is explained in the following Figure
Important facts in connection with the bulking of sand are as follows: