What must be prevented when fogging a concrete slab?

The correct choice focuses on the need to prevent the accumulation of water when fogging a concrete slab. Fogging is a technique used during the curing process of concrete, typically involving the use of mist or fog to control the hydration of the slab, especially in hot conditions.

Preventing water accumulation is crucial because excessive water pooling on the surface can lead to various problems. It can dilute the curing compounds, leading to inconsistent curing and surface issues. Moreover, standing water can create weak zones in the concrete, making it susceptible to defects such as scaling or flaking. Proper moisture management through fogging ensures that the concrete remains properly hydrated without an excess that could compromise its integrity.

While concerns like air bubbles, cracking, and extreme temperature variations are valid in the context of concrete finishing and curing, managing water accumulation specifically addresses immediate dangers that can arise from improper fogging techniques.