Seasonal Monitoring of Salt Movement in Masonry Materials

The recrystallization of salts due to changes in moisture content is one of the major damage functions in historic materials like natural stones, tiles, plasters, and mortars. This paper presents new results in the field of wireless monitoring of salt and moisture movement in mineral materials. Within the EU-project “Smart monitoring of Historic Structures – SMooHS” (www.smoohs.eu), a potential difference measurement node was developed in combination with electrodes based on silver/silver-chloride for the selective detection of chloride salts in porous masonry materials. Masonry walls placed in outdoors climate conditions in Bologna were preloaded by capillary suction with diluted NaCl solutions for several months. The salt migration and content were monitored with the developed wireless sensor system over a period of more than one year. The focus of the paper lies on the seasonal comparison of depth and height related variations of salt content.