Relationship between electrical resistance and single CNT fiber displacement relative to cement matrix – new insights on the electric polarization and spreading at debonded/slipped interface

New relationships between electrical resistance (r) at the CNT fiber-to-cement matrix interface and fiber-to-matrix displacement (u) are established, enhancing the accuracy of self-sensing technology for post-cracking concrete. In the experiment, micromechanical behavior and electrical response (steady and sweeping direct current, DC) were simultaneously monitored through a single-fiber pullout test. It revealed that significant polarization exists at the interface, leading to incorrect resistance measurement. The polarization is eliminated by adding carbon fibers to percolation; after that, an exponential increase of r with u was then observed in both fiber debonding and slippage stages, while r dropped right after full debonding. In the simulation, the spreading of electric current from a partially debonded/slipped interface to distant matrix bulk was computed with a multi-physics FEM model, to correlate resistance change with the interfacial damage level – debonding crack length and fiber slippage. The model-based parametric study showed that the r-u relationship is more sensitive to fiber conductivity than fiber dimensions or matrix conductivity.