Multifunctional cement composites with expanded graphite for temperature monitoring of buildings

The results of research on cement composites with expanded graphite for application in temperature monitoring are presented. Two series of cement mortars were prepared with expanded graphite obtained from intercalated graphite by rapid heating at 500°C and 1000°C. The relation between temperature and electrical resistivity and the thermoelectric properties of the mortars with expanded graphite were investigated. Based on the measurements, the temperature coefficient of resistivity and the Seebeck coefficient were determined. The change in resistivity with temperature in heating–cooling cycles and the change in thermoelectric voltage for temperature gradient cycling were studied. Furthermore, the long-term resistance and thermoelectric voltage of mortars exposed to atmospheric conditions were measured. The results indicate that cement composites with expanded graphite exhibit very promising properties for temperature monitoring. It was found the composites containing expanded graphite obtained at 500°C were better for temperature monitoring by means of the Seebeck effect, whereas composites with expanded graphite obtained at 1000°C were suitable for temperature monitoring by means of resistivity change. Moreover, the results revealed that the percolation threshold of expanded graphite should be exceeded in the cement matrix in order to apply these composites in temperature monitoring by means of change of resistivity.