As the temperature of the concrete mix increases, what happens to its slump?

• A. Increases
• B. Decreases
• C. No change
• D. Varies unpredictably

Answer: (B)

When the temperature of the concrete mix increases, the slump typically tends to decrease. This phenomenon occurs because higher temperatures can accelerate the hydration process of cement, leading to a quicker setting time. As the setting of the concrete accelerates, there is less time for the aggregate particles to rearrange and settle, which results in a stiffer mix and a lower slump. Essentially, the workability of the mix diminishes as temperature rises, making it less fluid and more difficult to mold.

In contrast, other considerations such as the use of certain admixtures or water-cement ratios can influence slump in different ways, but without those variables, the general behavior of concrete is that higher temperatures lead to a decrease in slump.