Bulking of Sand
The increase in moisture of sand increases the volume of sand. The reason is that moisture causes film of water around sand particles which results in the increase of volume of sand. For a moisture content percentage of 5 to 8 there will be an increase in volume up to 20 to 40 percent depending upon sand. If the sand is more fine there will be more increase in volume. This is known as bulking of sand.
Graphical representation of bulking of sand is shown below.
When the moisture content of sand is increased by adding more water, the sand particles pack near each other and the amount of bulking of sand is decreased. Thus it helps in determining the actual volume of sand, the dry sand and the sand completely filled with water will have the exact volume.
The volumetric proportioning of sand is greatly affected by bulking of sand to a greater extent. The affected volume will be great for fine sand and will be less for coarse sand. If proper allowance is not made for the bulking of sand, the cost of concrete and mortar increases and it results into under-sanded mixes which are harsh and difficult for working and placing.
To calculate the percentage of bulking of sand, the following test procedure can be used.
1. A simple container is taken and it is filled with 2/3 of the sand to be tested.
2. The height of sand is measured, for example say 200 mm.
3. Now, the sand is taken out of container. Care should be taken to see that there is no remains of sand should be there in the container during this transition .
4. Now the same container is filled with water.
5. Pour the sand in to the container filled with water and stir the sand with a rod.
6. Again, the height of sand is measured, say 160 mm.
Bulking of sand is calculated as, = (200-160)/160 = 40/160 = 1/4 (or) 25%.