Applied research tries to offer new materials from the slag mortars. Basic research tries to explore these engineered materials from the perspective of all the possible test methods. Modern vector analyzer R&S ZNC with a coaxial probe DAK-12 from Speag company was used to determine permittivity and dielectric loss factor of the beams and interesting spectrums of electric resistance were measured for samples with varying content of carbon powder. Carbon contributes from the viewpoint of electrical properties, for example it improved antistatic properties of the floor. In addition to the vector analyzer – the simpler measuring unit was also used. In a frequency range of 40 Hz to 1 MHz values of electrical resistance and permittivity values of the beams with different content of graphite powder, labeled Cond 896 were determined. The higher content of graphite powder increases the electrical conductivity; building materials based on cement are becoming more measurable using electromagnetic measuring methods. The most striking change in the relative conductivity was observed at excitation frequency of the external electric field of 1 kHz. At high frequencies of electrical excitation field from 10 MHz to 3 GHz values of the real part of permittivity were determined by vector analyzer. These measurements are among the building materials used rarely and they open new possibilities of diagnostics.
Building materials with enhanced electrical properties gain the importance in the new field of applications such as self-sensing or self-heating materials. In this paper, 3 mm long carbon fibres were used as a conductive admixture to alkali-activated slag mortar in order to reduce its resistivity. The amount of carbon fibres was ranging from 0.5 to 4.0% of the slag mass and the effect of the conductive admixture on the mechanical properties, electrical impedance, specific conductivity, and microstructure of alkali-activated slag composite was investigated. Only 0.5% of carbon fibres caused a significant decrease in impedance of alkali-activated slag composite and the addition of 4% reduced the impedance by one order of magnitude for low AC frequencies. However, due to problematic dispersion and higher demand of mixing water, the mechanical properties were deteriorated, especially at higher content of carbon fibres.
Alkali-activated slag is known as a building material for more than sixty years and is considered an alternative to Portland cement based binders. Compared to Portland cement it exhibits some superior properties such as higher resistance against chemical attack and exposure to elevated temperatures. Aluminosilicate binders are generally electrical insulators; however, electrical properties of building materials gain the importance in the new field of applications such as self-sensing or self-heating materials. This paper brings a comparison of the electrical properties, especially resistance and capacitance, between Portland cement and alkali-activated slag mortars. The measurements revealed that alkali-activated slag shows enhanced conducting properties due to the presence of mobile hydrated sodium ions and metallic iron microparticles.
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