Salt contaminated sandstone under environmental loading: recrystallization process and its consequences

Porous materials that contain salts can be permanently exposed to dissolution/deliquescencedrying cycles. Here we report that the mechanisms of salt precipitation are the key factors that determine the drying behaviour of salt contaminated porous materials and the physical weathering generated by salt precipitation. We present macroscopic and microscopic scale experiments, using magnetic resonance imaging, phase contrast microscopy, and X-ray tomography, assessing the impact of the recrystallization dynamics of NaCl and Na2SO4 on evaporation and damage observed in sandstone. When the same amount of water is used to dissolve the salt present in a stone, depending on whether this is done by a rapid saturation with liquid water or by a slow deliquescence using water vapor, different evaporation kinetics and salt weathering due to different crystallization pathways are observed.