Concrete structures in cold climates, such as those along roadsides, can retain moisture. This moisture makes them susceptible to frost-related damage when temperatures fall below freezing. Adding moisture worsens the damage during temperature fluctuations, leading to repeated freezing and thawing. De-icing salts, spread over these structures to melt ice, add to the freeze-thaw cycle, and draw even more moisture into the concrete.
This freeze-thaw cycle primarily causes surface scaling, where water seeps into the concrete and freezes, expanding and exerting pressure. This pressure can fracture the surface layer of the concrete, resulting in cracks and chips. When the water in the concrete pores freezes, it can create a thermodynamic imbalance with the surrounding gel water, causing more water to move in and freeze, thereby increasing the pressure. Also, the osmotic pressure from salts in the water can force more water into the pores, intensifying the pressure during freeze-thaw cycles.
Deeper within the concrete, D-cracking can develop near the edges and joints. These deep, D-shaped cracks indicate significant durability issues with the concrete. Concrete lacking air-entrained voids is most vulnerable to freeze-thaw cycles. These voids are tiny spaces within the concrete that act as buffers, allowing freezing water to expand without causing damage. Without these voids, the expansion results in more cracks and eventually leads to spalling, which occurs when parts of the concrete break away, weakening the overall structure.
