Damage potential and supersaturation of KNO3 and relevance in the field of salt damage to porous building material

Abstract

Salt crystallization is a major cause of damage in porous building materials. After accumulation of salts in a porous structure, damage occurs due to the crystallization pressure depending on the supersaturation of the pore solution. This study reports, for the first time, a systematic investigation of the damage potential of potassium nitrate. The supersaturation of bulk solutions and those confined in different porous materials was determined calorimetrically in cooling experiments and various factors influencing the metastable zone width were investigated. The study reveals significant supersaturations at the onset of crystallization within the porous materials which may generate high crystallization pressures. Similar supersaturations were also observed in evaporation experiments with solutions in glass capillaries. In addition, two types of damage tests were carried out with impregnated sandstone specimens. Significant deterioration observed in both tests confirm the high supersaturations during crystal growth within the pores. The results of these experiments support the understanding of the damage potential of potassium nitrate and show possible damage patterns as a result of cyclic crystallization and dissolution of the salt. Finally, all experiments confirm that potassium nitrate has a significant damage potential.