What is "concrete spalling" and what causes it?

Concrete spalling refers to the peeling or scaling off of the surface layer of concrete. This phenomenon often occurs when the concrete is exposed to significant stress, environmental conditions, or internal factors. The primary cause of spalling is typically related to the presence of moisture within the concrete that either freezes and expands or causes the concrete to deteriorate due to chemical reactions, such as salt exposure or corrosion of embedded steel reinforcement.

During freezing, the water inside the concrete expands, leading to internal pressure that can ultimately break the bond between the surface layer and the underlying concrete, resulting in chunks of material breaking away. Additionally, as steel reinforcement within the concrete rusts due to moisture and exposure to corrosive chemicals (like chlorides), it expands, contributing to spalling as it exerts pressure on the surrounding concrete.

Understanding spalling and its causes is critical for concrete maintenance and repair, as it can help in identifying potential issues before they lead to significant structural problems. Proper design, use of quality materials, and adequate environmental protections can mitigate the risk of spalling in concrete structures.