Physical salt weathering
Salt weathering is designated in the literature as ‘physical salt weathering’ to distinguish it from the effects of chlorides within concrete that may initiate reinforcement corrosion.
The mechanism of physical salt weathering is similar to freezing and thawing of water in concrete in that salts (usually salts of sulfates and possibly chlorides) crystallise in the pores of concrete close to its surface. The crystal growth exerts pressure and this can disrupt the concrete.
Salt in solution from groundwater or damp soil can be transported by capillary action vertically through a concrete member. Above ground level, the moisture is drawn to the surface and evaporates, leaving crystals of salt growing in the near surface pores. This results in an area of deterioration just above ground level. This form of attack is common in hot, dry areas and may also occur in marine structures.