What does spalling refer to in concrete?

Spalling in concrete refers specifically to the surface layer loss that occurs when the concrete surface flakes or peels away. This phenomenon is often due to various factors, such as freeze-thaw cycles, chemical reactions, or exposure to corrosive materials. When spalling occurs, it results in a weakened structural integrity and can compromise the durability of the concrete. This loss of surface material can also expose the underlying rebar, making it susceptible to further corrosion and deterioration.

In contrast, the other options describe different issues related to concrete. Visible cracks indicate fractures but do not inherently imply surface loss. Displacement of materials refers to the shifting of concrete sections, often due to settling or movement, rather than deterioration of the surface itself. Moisture absorption pertains to how concrete interacts with water but does not specifically address surface loss. Understanding spalling is crucial for assessing the condition of concrete structures and taking necessary remedial action to maintain their integrity.