Influence of ferrocyanide inhibitors on the transport and crystrallization processes of sodium chloride in porous building materials

Salt weathering leads to destruction of many valuable cultural heritage monuments and porous building materials. In order to reduce the impact of this, effective treatment methods are required. The use of crystallization inhibitors to mitigate salt damage has been proposed in the past; however, to date their effectiveness on cultural heritage objects has not been proven. Therefore a detailed experimental study to see the effect of crystallization inhibitors on the drying behavior of salinated porous materials has been undertaken. Two types of drying experiments were performed to observe the crystallization behavior of salt solutions with and without the presence of inhibitors: (1) in droplets of salt solution; (2) in porous supports (brick) contaminated with salt solution. From the droplet drying experiments it is shown that the presence of inhibitor results in higher supersaturation and changes the crystal morphology from cubic to dendritic crystals. In the brick drying experiments, due to the dendritic crystal morphology in the presence of inhibitor, advection becomes the governing phenomenon for ion transport. This results in the transport of salt ions to the outer surface of the brick, where crystallization results in the formation of nondestructive efflorescence. Meanwhile, inside the brick, higher supersaturation levels are not observed.