LU13997 - Crystallization in confined spaces, such as pores, is relevant to nearly every field of science. Salts crystallizing within porous materials exert a pressure that contributes to damage, but the quantification of this in-pore pressure is very difficult to achieve. Salt-induced physical weathering has been documented as a substantial damage mechanism in nearly every environment all over the world from pharaoh’s tombs in Egypt, the cathedrals of Europe, decorated caves in China, Mayan pyramids in Mexico and Central America and historic buildings in the United States and England. In this paper, we calculate the solution supersaturation and resulting crystallization pressure and unequivocally identify the precipitating phase in a multi-phase salt system (containing hydrous and anhydrous, metastable and stable phases). These results help to explain why salts, such as Na2SO4 with various hydrated phases are more damaging than single phase salts such as NaCl. We also show that damage associated with meta-stable phase transitions can be suppressed by the use of crystallization promoters. These results point to new ways to prevent salt damage to building materials by bypassing metastable phase formation.
