Dynamic electrical properties of lightweight cement mortars with waste graphite additive
Waldemar Pichór
Quarterly No. 2, 2010 pages 175-180
DOI:
keywords: cement composites, lightweight mortars, graphite, Seebeck effect, smart materials
abstract This paper presents the results of investigation dynamic electrical and thermoelectric properties of lightweight cement mortars with cenospheres from coal ash and waste graphite powder additive. Quartz sand was replaced by aluminosilicate cenospheres up to 60% of mass. The replacement sand led to significant reduction of bulk density and thermal conductivity of cement mortars. The waste graphite powder obtained during mechanical treatment of metallurgical electrodes production was used as the conductive filler. Graphite powder was added up to 35% of cement mass. The main physical properties: bulk density and thermal conductivity were investigated. Addition of graphite powder above percolation threshold changed the character of electrical conductivity of cement mortars. Reduction of resistivity is very strong. In case of mortars with 35% cement replacement by graphite powder the Seebeck voltage was measured. Addition of graphite powder to mortars led to moderate detoriation of main properties but cement mortars but got possibility of reaction due to the temperature changes. The Seebeck coefficients calculated for all investigated mortars were similar (in error range) and weak dependence of temperature gradient was in each case. But in typical application the thickness of used mortars were very small (about 1÷2 cm) and the changes were to small to induce measurable level of thermoelectric force. The point is that in case of lightweight mortars the low thermal conductivity caused much higher temperature gradient and consequence the Seebeck voltage increased. The dynamic measurements of electrical conductivity and Seebeck effect were done. The electrical resistivity of mortars during cyclic load were changed up to 28% for mortars with maximal amount of aluminosilicate cenospheres. The changes were reversible. In case of Seebeck voltage the effect of time constants of reaction on the immediately temperature change were measured. The effect of thermal conductivity was visible. Lightweight cement mortars with conductive particles as graphite powder are multifunctional materials and may be used to monitor the temperature of building’s wall.