When should additional water be added to maintain slump?

The answer regarding when additional water should be added to maintain slump is particularly relevant when considering the impact of temperature on concrete mixing and placement. When the temperature increases, the rate of water evaporation from the surface of freshly mixed concrete can rise significantly. This can lead to a decrease in slump, which is a measure of the workability and consistency of the concrete mix.

In high temperatures, the concrete may also begin to set more quickly, further compounding the issue of workability. By adding water at this stage, the concrete mix can retain its desired consistency, making it easier to work with and ensuring that it achieves proper compaction and performance.

While there are other scenarios, such as dry conditions or fast setting mixes, where water adjustments might be needed, the specific context of temperature changes directly impacts the consistency and workability of the concrete mix, which is why this choice is the most appropriate.