Synergistic effects of hybrid fiber reinforcement and orientation on the conductivity and self-sensing properties of alkali-activated mortars

Self-sensing concrete has attracted increasing attention as a multifunctional material with promising applications in intelligent infrastructure. This study introduces a synergistic strategy combining steel fibers (SFs) and nickel-coated carbon fibers (NCFs) with controlled orientation to enhance the conductivity and self-sensing performance of alkali-activated conductive mortars (AACMs). The effects of fiber hybridization and orientation on mechanical, electrical, and piezoresistive properties were systematically investigated. Parallel-oriented SFs significantly improved the mechanical performance, achieving compressive and flexural strength exceeding 100 MPa and 11 MPa, respectively, at only 0.4 vol.%. Incorporating 0.05 vol.% NCFs into parallel-oriented SF-reinforced AACM reduced resistivity from 4.7 × 10 3 Ω·cm to 8.15 Ω·cm, resulting in enhanced self-sensing performance. X-ray CT characterization quantified fiber alignment and dispersion through the orientation factor (α) and dispersion coefficient (β), revealing that fiber settlement in randomly oriented mixtures (β = 0.532) disrupted conductive networks. The application of a magnetic field not only contributed to fiber orientation but also enhanced fiber dispersion (α = 0.919, β > 0.7) in AACM. AC impedance spectroscopy confirmed reduced charge–transfer resistance at the fiber–matrix interface. These findings provide a feasible strategy for the design of multifunctional and sustainable AACMs with high conductivity and reliable self-sensing performance. • AACMs with 0.4 vol% .SF and 0.05 vol% .NCF achieved compressive strength exceeding 100 MPa and ultra-low resistivity (8.15 Ω·cm) through parallel fiber orientation. • Hybridization of SFs and NCFs significantly enhanced piezoresistive performance. • The effects of fiber orientation and dispersion on resistivity and piezoresistive performance were quantitatively evaluated. • Fiber hybridization enhanced charge transport at the fiber–matrix interface.