How is the slump of concrete selected? Give an example.

Most of the time it doesn’t matter, but there are three cases I know of that do:

1. Most common is workability. The higher the slump the easier it is to move around once poured. 3″-4″ is usually taken as the baseline.
2. Indication of water content. The water content will determine strength values during cure times. Also, less water can speed up cure times in some types of concrete with the understanding that the strength profile will continue to increase over time.
3. Indication of lateral loads imposed by concrete. Low or zero slump concrete is more self-supporting than high slump concrete. Therefore, it can be calculated how much force the concrete will apply to the forms or other containing structures.