What should be added to sand to achieve optimum compaction?

To achieve optimum compaction in sand, adding water is essential. Water plays a crucial role in the compaction process because it helps to fill the voids between the sand particles, creating a denser and more stable mixture. When water is added, it acts as a lubricant, allowing the sand particles to slide past one another more easily, which enhances the compaction process.

Furthermore, the correct amount of water promotes the formation of a temporary bond between the sand grains through surface tension, which further aids in achieving a well-compacted state. If too little water is present, the particles cannot achieve maximum density because they will not settle together adequately. Conversely, too much water can lead to a condition known as "over-saturation," where the particles lose their frictional ability and may result in weaker compaction. Therefore, finding the right moisture content is essential for ensuring optimum compaction of sand.