What is a potential problem if evaporation exceeds the rate of bleed in fresh concrete?

When evaporation surpasses the rate of bleed in fresh concrete, a critical issue that arises is the risk of plastic shrinkage cracking. In the initial setting phase of concrete, as the water from the surface evaporates more quickly than it can bleed to the surface, the concrete can develop tensile stresses. These stresses can exceed the tensile strength of the uncured concrete, leading to the formation of cracks while the concrete is still in a plastic (unset) state.

Plastic shrinkage cracking is a significant concern, especially in hot, dry, and windy conditions where evaporation rates are heightened. The presence of these cracks can compromise the aesthetic and structural integrity of the concrete surface. Therefore, monitoring and controlling the moisture loss during the setting period is crucial to prevent such cracking.