Monitoring of salt content in mineral materials using wireless sensor networks

The recrystallization of salts due to changes in moisture content is one of the major damage mechanisms in historic materials like natural stones, bricks, plasters, and mortars. This paper presents a new development in the field of wireless monitoring the salt content in historic mineral materials. In this investigation ion selective potential sensors (electrodes) are used for monitoring salt displacement in time, influenced by changes in moisture content. Different kind of electrodes and electrode couplings are tested in laboratory, and in field measurements. For measuring the potential, low power data acquisition hardware was developed that is optimized for using it in wireless sensor networks. Data acquisition uses a competitive wireless sensor network system that is further developed in the SMooHS-Project (Smart Monitoring of Historic Structures, Collaborative Project in the 7^th Framework Programme of the EU) to operate under harsh environments. First results of the laboratory and field test are presented, showing that long-term monitoring of salt content is feasible.