The electrical properties of concrete are gaining their importance for the application in building construction. In this study, graphite powder was added to alkali-activated slag mortar as an electrically conductive filler in order to enhance the mortar’s conductive properties. The amount of graphite ranged from 1% to 30% of the slag mass. The effect of the graphite powder on the resistivity, capacitance, mechanical properties, and microstructure of the composite was investigated. Selected mixtures were then used for the testing of self-sensing properties under compressive loading. The results show that the addition of an amount of graphite equal to up to 10% of the slag mass improved the electrical properties of the alkali-activated slag. Higher amounts of filler did not provide any further improvement in electrical properties at lower AC frequencies but caused a strong deterioration in mechanical properties. The best self-sensing properties were achieved for the mixture with 10 wt% of graphite, but only at low compressive stresses of up to 6 MPa.

Concrete setting and hardening designate the concrete grade. The impedance spectroscopy method, as one of the non-destructive testing method group, was used to characterize concrete specimens and track the changes in the concrete spectrum. Variances in the tan δ (f) and Im Z(f) or Re Z(f) of the specimens under investigation have been observed. The specimen quality has been described by means of the loss type prevailing in the material. The results of this study are expected to provide information about the correlation between the n-factor and the concrete setting time.

By incorporation of nanotubes to the current composite materials, their properties can be significantly improved. Carbon nanotubes can act as filler, which minimizes the air gaps content in the matrix. The denser structure positively affects the physical and mechanical properties of the whole composite. The paper deals with alkali-activated materials (AAM) based on finely-ground granulated blast furnace slag modified by carbon nanotubes. Prismatic samples of this type of AAM were prepared with addition of 0.1 – 0.4wt. % of carbon nanotubes (with 0.1% step). The change of electrical parameters (electrical capacity, relative permittivity, real and imaginary impedance component) was observed. The obtained results indicate that the absolute value of the impedance decreases with increasing amount of carbon nanotubes and relative permittivity shows the general increase. The results may contribute to further research and development of alkali-activated systems, focusing on practical applications in construction

The development of smart materials is a basic prerequisite for the development of new technologies enabling the continuous non-destructive diagnostic analysis of building structures. Within this framework, the piezoresistive behavior of fly ash geopolymer with added carbon black under compression was studied. Prepared cubic specimens were doped with 0.5, 1 and 2% carbon black and embedded with four copper electrodes. In order to obtain a complex characterization during compressive loading, the electrical resistivity, longitudinal strain and acoustic emission were recorded. The samples were tested in two modes: repeated loading under low compressive forces and continuous loading until failure. The results revealed piezoresistivity for all tested mixtures, but the best self-sensing properties were achieved with 0.5% of carbon black admixture. The complex analysis also showed that fly ash geopolymer undergoes permanent deformations and the addition of carbon black changes its character from quasi-brittle to rather ductile. The combination of electrical and acoustic methods enables the monitoring of materials far beyond the working range of a strain gauge.

Concrete quality depends on various stress factors. The impedance spectroscopy method, as one of the non-destructive testing method group, was used to characterize concrete specimens and track the changes in the concrete spectrum after heat stress. The temperature range was between 0°C and 1200°C. Variances in the tan δ (f) and Im Z(f) or Re Z(f) of the specimens under investigation have been observed. The specimen quality has been described by means of the loss type prevailing in the material. The results of this study are expected to provide information about the correlation between the relative permittivity and changes in the structure for heat stress samples.