What causes excessive bleeding in concrete?

Excessive bleeding in concrete primarily occurs due to the presence of too much water in the mix. When concrete is mixed with an excessive amount of water, the water-to-cement ratio is increased beyond the ideal levels. As the concrete begins to set, the excess water rises to the surface, creating a phenomenon known as bleeding. This causes a layer of water to appear on top of the concrete, which can lead to various issues, such as a weakened surface, reduced durability, and poor bond strength with subsequent layers or finishes.

While air, temperature, and humidity can indeed affect the properties and setting behavior of concrete, they do not directly cause excessive bleeding in the same way that an over-watered mix does. High air content can actually improve concrete's workability, too low temperatures can slow the setting process, and high humidity can influence curing but are not the primary factors leading to the excessive bleeding that stems from an imbalanced water ratio.