Mechanisms of damage by salt Geological Society, London, Special Publications

Limestone is very susceptible to the aggressive action of salts. This paper describes the current understanding of the mechanisms by which salt crystallization causes damage to limestone. Crystallization pressure increases with the supersaturation of the solution, which may result from rapid drying and/or decrease in temperature. Salts with a tendency to achieve higher supersaturation owing to a high nucleation barrier are potentially able to induce more severe damage. In the presence of small pores (,100 nm), equilibrium thermodynamics indicates that crystallization pressure can result from the curvature dependence of the solubility of a salt crystal. Under nonequilibrium conditions, high transient stresses can occur even in larger pores. In the field, the complexity of salt weathering results from heat, moisture and ion transport coupled with in-pore crystallization during changing climatic conditions. This paper describes how progress in the modelling and numerical simulation of these coupled processes can contribute to a better understanding of the influencing factors and assessment of critical conditions. Classically, tests such as the bursting test and the capillary rise experiment with simultaneous evaporation have been applied to evaluate qualitatively stone deterioration induced by salt crystallization. More recently our group has introduced other experimental methods to the field of salt weathering that provide quantitative information about nucleation and crystallization kinetics in porous materials (by differential scanning calorimetry), induced deformation and stress (by dynamic mechanical analysis and a novel warping test), and pore clogging caused by in-pore