Explanation:
When sand particles come in contact with water, they tend to form a thin film around them. This film of water acts as a lubricant between the sand particles and reduces the friction between them. Due to the reduction in friction, the sand particles tend to move apart, resulting in an increase in volume, which is known as bulking of sand.

The bulking of sand is influenced by various factors such as particle size, shape, texture, and moisture content. Among these factors, moisture content plays a significant role in determining the extent of bulking.

Effect of moisture content on bulking of sand:
The bulking of sand increases with an increase in moisture content up to a certain maximum value and then decreases. This behavior can be explained based on the following stages:

Initial stage:
At this stage, when the sand is dry, there is no bulking as there is no lubrication between the particles.

Stage of increasing bulking:
When a small amount of water is added to the sand, the water forms a film around the particles and reduces the friction between them. This results in an increase in volume, which is known as bulking. As the moisture content increases, the bulking also increases.

Stage of maximum bulking:
At a certain moisture content, the bulking reaches a maximum value. This is because the water film around the particles has reached its maximum thickness, and any further increase in moisture content will not result in any significant increase in bulking.

Stage of decreasing bulking:
At this stage, when the moisture content is further increased, the excess water fills the voids between the sand particles and causes them to come closer. This results in a decrease in volume, which is known as contraction. Hence, the bulking decreases with an increase in moisture content beyond the maximum value.

Conclusion:
Thus, the bulking of sand first increases to a certain maximum value and then decreases with an increase in moisture content. Understanding the bulking behavior of sand is essential in various construction activities such as concrete mix design, plastering, and masonry work.