Characterization of interface impedance between conductive CNT fiber and carbon fiber-reinforced cementitious composite (FRCC) matrix

Electrical impedance (Z) of the interface between conductive fiber and cement matrix is studied by applying alternating current to carbon fiber-dosed cement cylinders holding a CNT fiber (working electrode) and exterior copper tape (counter electrode). Distinct impedance behaviors are seen because of different carbon fiber percolations—whether they cause interfacial polarization or induction (L). Based on these percolation conditions, multiple equivalent circuits for predicting the impedance are established and validated by introducing distributed elements like constant phase element (CPE) and diffusion impedance (Z_diff). All these circuits consist of modules specific for the CNT-to-matrix interface, the cement matrix, and the copper-to-matrix, so they can quantify the resistance (R) and capacitance (C) of these components separately. Such an experiment-modelling combined procedure forms a new method of determining the fiber-to-matrix interfacial resistance and capacitance. And it is used to study the effect of carbon fiber length on these electrical properties. The results reveal neglected interfacial impedance between exterior copper electrode and the matrix when the carbon fiber length is increasing. However, the alteration in the length hardly affects the time constant (characteristic frequency) of each module once electrical percolation was reached. The new method prepares for the post-cracking self-sensing technology of fiber-reinforced concrete, where the impedance-revealed fiber-to-matrix interfacial damage is critical.