Self-heating potential of geopolymer metashale mortars with graphite powder

Geopolymers are eco-friendly materials with favorable material properties and, therefore, suitable candidates for optimization in terms of electrical properties which broadens their potential in self-heating, self-sensing, or energy harvesting applications. The effectivity of self-heating function crucially depends on the presence of a sufficient number of conductive paths in a non-conductive material matrix corelating with the effective electrical conductivity of the material. The optimization of self-heating function, therefore, consists in appropriate dosing and homogenization of supplementing electrically conductive admixtures, as well as correct embedment of electrodes ensuring good contact with the material. The paper is focused on the design of multifunctional geopolymer mortar based on metashale precursor that was activated by a mix of potassium hydroxide and silicate. Electrical properties of the composite were optimized by graphite powder in the amount of 3 wt% and electrical experiments were performed using embedded copper grid electrodes. The material was characterized in terms of basic physical, mechanical, thermal, and electrical properties. The consecutive self-heating experiment was performed under the AC voltage of 130 V RMS with the initial power at the beginning of the measurement of 10 W. It was observed power increase of approximately 3 W and 25 °C rise of temperature during the 2 h lasting experiment.