To what degree can a 20°F increase affect the slump?

A 20°F increase in temperature can lead to an increase in the slump of concrete due to the accelerated hydration process of the cement at higher temperatures. When the temperature rises, particularly in hot weather, the water in the mix becomes more active, causing the concrete to become less viscous. This results in a more fluid mix, which typically translates to an increase in slump.

In practical terms, as the hydration process speeds up, the concrete mixture becomes easier to work with and flows more freely, contributing to a higher slump measurement. While various factors can influence the exact amount that the slump increases, the general principle that higher temperatures lead to increased slump holds true.

This understanding is crucial for concrete inspectors and any construction professionals involved with concrete placement, as it impacts workability, setting times, and ultimately the quality of the finished product.