Investigation on the Relationship between Mechanical and Electrical Properties in Single CNT Fiber Pullout from Cement-based Matrix via Electrochemical impedance spectroscopy (EIS) Method

The feasibility of predicting the failure of fiber/matrix interface with electrical signals could be further developed into a unique self-sensing technology to monitor the post-cracking behavior (e.g., the very fine crack width) in conductive fiber-reinforced cementitious composite (c-FRCC), based on bottom-up scale-linking micromechanics. In the study, micromechanical behavior and steady electrical impedance were captured via a single carbon nanotube (CNT) fiber pullout testing and EIS measurement. It revealed non-linear cylindrical diffusion behavior at the low frequency, which shadowed the contribution of the fiber-to-matrix interfacial damage to the electrical response. For better quantitative analysis of reflecting mechanical and electrical correlation based on interfacial microstructure, chopped polyacrylonitrile (PAN) based carbon fibers were added to the percolation. After that, distinct physics-based impedance arcs were exhibited vis the EIS testing, corresponding to the matrix (high-frequency domain), fiber-to-matrix interface (intermediate frequency domain), and electrode-to-matrix interface (low-frequency domain), respectively. An exponential increase of resistance (r) with fiber displacement (u) was then observed in both the debonding and slippage stages. The contribution of each phase directly revealed that the change in the total electrical resistance (∆r) was mainly attributed to the matrix (high-frequency domain) via EIS analysis. During debonding, the weak disconnection of the CNT fiber and matrix compromised the conductive path in the matrix, while the dislocation of the CNT fiber relative to the matrix due to slippage altered the conductive path and both contributed to ∆r. The finding would be helpful in establishing electrical and mechanical modeling for the future parametric study and sensitivity analysis of the r-u relationship, further exploring the electrical and mechanical (like crack width) correlation of c-FRCC under the fiber bridging level.