Electrical response and damage self-sensing mechanisms of fiber-reinforced coal gangue concrete

To address the challenge of structural health monitoring for coal gangue concrete (CGC) under complex service environments in deep mine backfill engineering, this study proposes a self-sensing CGC based on a fiber composite system. Using in-situ electrochemical impedance spectroscopy (EIS), the electrical response mechanisms of carbon fiber (CF) and steel fiber (SF) reinforced CGC were systematically evaluated under mechanical loading, single freeze-thaw cycles, single sulfate attack, and severe coupled freeze-thaw and sulfate erosion. The results demonstrate that fiber modification exhibits a significant mechanical threshold effect. The complementary action of an optimal hybrid fiber system and high-density aggregate constructs a dense and integrated load-bearing network, elevating the 28-day compressive strength to a maximum of 25.5 MPa. Furthermore, the macroscopic self-sensing response of CGC highly relies on a dual sensing mechanism governed by the moisture state of the matrix. Under mechanical damage in a conventional unsaturated state, microcracks physically sever the solid-phase conductive network, manifesting as an increase in electrical resistance with progressive damage. Conversely, under water-rich erosive environments such as coupled freeze-thaw and sulfate attack, newly generated microcracks induced by crystallization expansion pressure are rapidly filled with highly conductive pore solutions. This proliferation of ion transport channels paradoxically reverses the electrical trend, resulting in a significant decrease in equivalent resistance as structural deterioration intensifies. Specifically, a distinct functional division exists between the two fibers across different damage stages: micro-scale CF effectively restricts the initiation of early-stage microcracks and provides localized electron-hopping pathways, whereas macro-scale SF dominates in the later stages by bridging macroscopic cracks and ensuring the long-distance continuity of the conductive sensing network. Based on the intrinsic matrix resistance R 1 decoupled from the EIS equivalent circuit, an electrical damage degree (D) model was established. This model, highly consistent with the physical reality of the increase in harmful macro-pores and the expansion of erosion products, successfully quantifies and captures the three-stage nonlinear failure characteristics (incubation-acceleration-stabilization) of CGC under coupled erosion. This study establishes an accurate electrical quantitative mapping paradigm from microscopic pore deterioration to macroscopic structural damage, providing a reliable theoretical foundation for the long-term, in-situ, non-destructive monitoring of mine backfill structures under complex conditions.