Salt Crystallization on Crazannes Limestone in a Long-Term Storage Environment

This study focuses on the damage caused by salt crystallization and the associated weathering processes in Crazannes limestone during storage. The main objective was to understand the factors contributing to the limestone's observed flaking and granular disintegration, which cannot be attributed to frequent salt crystallization cycles experienced in outdoor exposure. Porosity and chemical analyses were performed to identify the salt minerals and their distribution within the stone's microstructure. Chemical analyses revealed the presence of gypsum on the powdery weathered residues and stone surface, while halite was consistently found throughout the samples, with higher concentrations on the surface. The storage of the blocks in a closed room led to moisture evaporation and an increase in relative humidity (RH) ranging from 60% to 75%. Under these conditions, the gypsum crust remained relatively stable. The threshold for halite crystallization decreased to 65% RH in the presence of other salts. Consequently, even slight fluctuations in RH (%) caused by seasonal variations could induce cycles of NaCl crystallization and dissolution, resulting in damage behind the gypsum crust that protects the surface. Despite gypsum and halite not being the most aggressive salts, the porous nature of Crazannes limestone made it highly susceptible to salt-induced deterioration, leading to significant damage during storage, even with a minimal number of cycles. These results highlight the importance of controlling the storage conditions when stones are contaminated by salts.