Frequency-dependent AC response of cement-based materials: New insights from decoupled admittance analysis

Alternating current impedance spectroscopy (ACIS) has been widely employed to measure the electrical properties of cement-based materials for the characterization of hydration and microstructure. However, its accuracy is inherently limited by several ambiguities, including “dielectric amplification”, ACIS dispersion, and the frequency dependence of fitted impedance parameters. In this study, a decoupled admittance analysis (DAA) methodology, without predefined assumptions, was developed to investigate AC response in cement-based materials (CBMs) and thus determine the dielectric constant and pore conductivity. Results demonstrate that the “dielectric amplification” artifact stems from geometric mismatches or misalignment of polarization directions, resolvable through specimen thickness optimization. Three dynamic mechanisms drive ACIS dispersion and frequency-dependence of fitted impedance parameters: progressive coupling of disconnected/connected pore resistances, matrix-to-electrical double layer (EDL) capacitance transition, and EDL decay with frequency. Resistive disparities between connected and disconnected pores reflect distinct chloride transport patterns, necessitating pore-specific modeling for durability prediction. These findings enable physically interpretable characterization of the dielectric constant and pore conductivity in CBMs, thereby enhancing the potential of ACIS for real-time, non-destructive monitoring of concrete microstructure and hydration evolution in field applications. • DAA clarifies frequency-dependent AC response in cement-based materials. • DAA removes dielectric artifacts via thickness optimization for accurate ε ’ measurement. • ACIS dispersion arises from pore resistance, capacitance transition, and EDL decay. • Pore conductivity contrast confirms chloride transport heterogeneity. • DAA enables real-time monitoring of hydration and microstructure evolution.