Conductive Network Evolution and Self-Sensing Mechanism of Carbon Fiber Asphalt Concrete Based on Electrical Impedance Spectroscopy

Abstract

To overcome the problems of poor durability and structural incompatibility inherent in conventional urban traffic monitoring technologies, this study develops a self-sensing asphalt concrete composite incorporating carbon fiber (CF) as a conductive functional filler to construct an internal conductive network. The effects of CF dosage and loading rate on the electrical and dynamic piezoresistive characteristics of the composite were systematically investigated. Furthermore, the evolution mechanism of the micro-conductive network was revealed via electrochemical impedance spectroscopy (EIS) coupled with equivalent circuit modeling. The results demonstrate that the electrical resistivity follows a two-stage percolation behavior (“sharp decline followed by stabilization”) with increasing CF content, yielding a percolation threshold of 0.2 wt%. As CF dosage increases, the Nyquist plots transition from quasi-linear profiles to a fully developed single semicircle, and eventually to an alternating pattern of high-frequency capacitive arcs and low-frequency diffusion impedance. Equivalent circuit analysis reveals that higher CF loadings reduce both contact and tunneling resistances while simultaneously elevating interfacial capacitance. Under monotonic loading, the developed conductive network enables enhanced piezoresistive responses, and the 0.2 wt% group achieves the most pronounced improvement relative to the 0.1 wt% group, with the maximum resistivity change rate and stress sensitivity increasing by 82.05% and 313.59%, respectively. Moreover, the specimens exhibit the optimum piezoresistive response under a dynamic loading rate of 250 N/s. This study clarifies the variable-frequency sensing mechanism of self-sensing asphalt concrete, providing scientific guidance for dynamic speed measurement and weigh-in-motion (WIM) monitoring in smart pavements.