What should be added to sand to achieve optimum compaction?

To achieve optimum compaction of sand, it is important to add water. When water is incorporated into the sand, it fills the voids between the sand particles and creates a cohesive bond that allows for better packing. This process increases the density of the sand as the particles are pushed closer together, decreasing the volume of air pockets within the material.

Water also serves as a lubricant, enabling the sand grains to shift and rearrange into a more compact arrangement. This is particularly relevant in construction and excavation practices, where achieving maximum density is essential for the stability and load-bearing capacity of various structures.

While air may be present in the voids of sand, it does not contribute to compaction. Gravel and cement can influence the properties of soil mixtures but are not the optimal additives for enhancing the compaction of sand specifically. Thus, adding water is the most effective approach to ensure optimal compaction in sandy materials.