What is a common cause of spalling in concrete surfaces?

Spalling in concrete surfaces is primarily caused by freeze-thaw cycles and chemical exposure. When moisture penetrates the concrete and then freezes, the expansion of water as it turns to ice can create significant pressure within the concrete. This cyclic process leads to the cracking and flaking of the surface, commonly known as spalling.

Additionally, chemical exposure, such as from de-icing salts or sulfates, can further degrade the surface integrity of concrete. These chemicals can react with the concrete matrix, weakening it and leading to surface flaking and breakdown. The combination of these factors makes freeze-thaw cycles and chemical exposure a prevalent cause of spalling.

Other options, while potentially problematic in different contexts, do not typically lead to spalling in the same direct manner as freeze-thaw cycles and chemical interactions do.