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 finer 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.