Spalling occurs on exterior slabs when water that is trapped in the concrete goes through multiple freezes and thaws. When water freezes it expands by about 9%, which creates tremendous pressure inside the slab.

What is the cause of spalling?

What is spalling? ... There are a number of reasons why spalling occurs including freeze thaw cycling, the expansive effects of Alkali Silica Reaction or exposure to fire. However, the most common cause of spalling is the corrosion of embedded steel reinforcement bars or steel sections.

What are the causes of spalling in concrete?

There are many causes of concrete spalling; they include the improper placement of concrete and its reinforcing, electrochemical (galvanic) reactions between embedded metals within the concrete matrix, and corrosion of embedded reinforcing steel due to exposure to water and/or chemicals.