Saline Water Evaporation and Crystallization-Induced Deformations in Building Stone: Insights from High-Resolution Neutron Radiography

To assess salt damage risks in building materials and geomaterials, the key components to identify are the accumulation of salts and the damage propagation. Experimental data combining both are scarce but offer an additional richness for understanding the coupling between transport and mechanics in the context of salt crystallization in porous media. Here, we quantify the drying of sodium sulfate and sodium chloride solutions from Savonnières limestone together with the damaging character of anhydrous sodium sulfate and halite precipitation, respectively. Repeated wetting–drying cycles are performed, by using salt solutions in the rewetting phase and by drying at an elevated temperature of 45 °C. The drying and deformation dynamics are characterized by means of high-resolution neutron radiography, with a moisture content resolution of 0.04 kg/m3 and a spatial resolution of 13.5 μm/pixel. Precipitation occurs inside the specimen by treating the upper volume of the specimen hydrophobically. High Peclet numbers are found, representing a long first drying stage leading to salt accumulation in a localized zone, increasing the damage risk. In-pore crystallization of halite during drying of 5.8 molal sodium chloride solutions is particularly damaging for our type of samples. Large deformations are observed already during the first cycle, indicative of crack formation. With 1.4 molal sodium sulfate solutions, no damage is observed upon precipitating the anhydrous sodium sulfate crystal, but the drying rate decreases with every cycle due to augmented pore clogging.