A Comparison of the Resistance- and Capacitance-Based Sensing of Geopolymer and Cement Composites with Graphite...

Aluminosilicate binders, such as Portland cement or geopolymers, are generally considered electrical insulators. In order to decrease their electrical resistance, electrically conductive fillers are added. This brings new application possibilities, such as the self-sensing and self-monitoring of smart structures. In this study, three different aluminosilicate composites with the same amount of fine graphite filler (6% with respect to the basic aluminosilicate raw material) were tested for resistance- and capacitance-based self-sensing properties. Portland cement and two geopolymer binders were used as the basic matrices for the conductive composites. The composites were tested for self-sensing properties in repeated compression in the elastic area, static mechanical properties, and microstructure using scanning electron microscopy and mercury intrusion porosimetry. The results showed that alkali-activated materials are less stiff than Portland cement composite; however, they provide better self-sensing properties, regardless of the measured electrical parameters. The highest capacitance-based gauge factor 74.5 was achieved with the blended slag/fly ash geopolymer composite, whereas the cement composite showed very poor sensitivity, with a gauge factor of 10.2. The study showed a new possibility of self-sensing based on the measurement of capacitance, which is suitable for geopolymers and alkali-activated composites; however, in the case of cement composites, it is very limited.