The durability of 0.44 W/C concrete under simulated Arctic conditions was studied. The length change of concrete specimens was monitored throughout the test. Samples taken from the concrete specimens before and after the test were analyzed to determine the effects of simulated Arctic conditions on the microstructure of the concrete. The results showed that the alternating conditions of immersion in seawater and exposure to cold air mostly affect the surface layer of the concrete and facilitate a deep migration of aggressive ions like magnesium and sulfate.