The volume expansion occurring on conversion of water to ice and associated water movement cannot be accommodated in fully saturated concrete. The drier the concrete, the more capacity it has to absorb the pressures associated with ice formation and water flow under hydraulic and osmotic influences. Thus minimising the degree of saturation of the pore structure is an important controlling parameter.
Concrete structures at greatest risk of saturation are those permanently exposed to water and those occasionally exposed to water under pressure. Deicing agents also encourage saturation because the critical relative humidity below which drying is induced for a pore of given radius increases as the solute concentration of the pore liquid increases (Harrison et al., 2001). Free water in the concrete is not only influenced by the environment but also by the detailing of the elements of the structure. Drainage features that minimise the contact time between water and concrete are particularly beneficial.
