Durability Design of Concrete Structures

5Salt Crystallization

This chapter treats the damage of structural concrete by salt crystallization. This phenomenon is also termed “salt weathering” for other porous building materials, such as stones and bricks. As the external salts are deposited on or transported to the surface of concrete elements, the pore solution of concrete can be supersaturated with respect to the salts under the temperature fluctuations or drying–wetting actions in environment. The pore pressure can accumulate as salt crystals form in pores, high enough to fracture the solid matrix and induce damage to concrete. Though the resulting damage is usually manifested as surface scaling, the mechanical resistance of concrete can be affected in extreme situations. This chapter begins with the introduction of the phenomena of salt crystallization for concrete elements and structures, then it details the mechanisms of salt crystallization in confined pores. Since both pore freezing and salt crystallization involve crystallization in confined pores, some common concepts and expressions from Chapter 3 are adopted. Salt crystallization in concrete is still an ongoing subject with much knowledge to be explored, so the models in this chapter are conceptual, attempting to capture the main mechanisms of pore crystallization. Finally, the basis for durability design against salt crystallization is provided.

5.1 Phenomena and Observations

Salt crystallization belongs to weathering actions of the natural environment ...