Factors that govern the electrical, dielectric, and electromagnetic properties of hardened fly ash-based geopolymer composites

Abstract

This study investigates the factors influencing the electrical, dielectric, and electromagnetic properties of fly ash-based geopolymer pastes (GP) by comparing their electrical resistivity, relative permittivity, and electromagnetic interference (EMI) shielding effectiveness under varying design parameters, including the water-to-binder (W/B) ratio, alkali modulus, and slag content. The results reveal that both DC and AC resistivity increase with a lower W/B ratio, higher alkali modulus, and greater slag content. Conversely, relative permittivity increases with a higher W/B ratio, lower alkali modulus, and greater slag content. These electrical and dielectric properties are interrelated, as they both depend on microstructural characteristics and their effects on charge movement and concentration. The predominant EMI shielding mechanism, whether reflection or absorption, is determined by the design parameters. Specifically, a higher W/B ratio correlates with greater reflection loss due to high relative permittivity and conductivity. A higher alkali modulus is associated with increased total shielding loss, also driven by high relative permittivity and conductivity. When slag content is increased, high resistivity combined with moderate relative permittivity leads to higher total shielding loss. The reflection of electromagnetic waves by GP is attributed to the impedance mismatch between the GP and air, while absorption results from conduction loss and polarization losses, including dipolar polarization, polarization relaxation, interfacial polarization, and molecular currents. This study provides valuable insights into the potential of geopolymers as functional materials.