Mechanism of concrete deterioration due to salt crystallization

Surface scaling of concrete is observed due to salt crystallization. The salts present on concrete as efflorescence or subflorescence are usually highly soluble in water. The most common efflorescent material is anhydrous sodium sulfate (Na2SO4, thenardite) and hydrous sodium sulfate (Na2SO4·10H2O, mirabilite). Various mechanisms have been proposed concerning the cause of this form of deterioration: (a) the solid volume change from the thenardite to mirabilite; (b) salt hydration pressure; and (c) the salt crystallization pressure. All three mechanisms are reviewed and discussed in the present paper.