Multifunctional concrete for shrinkage-resistant structural health monitoring without carbon-based additives under fluctuating temperature and humidity

Self-sensing concrete uses nanomaterials that are environmentally unstable. This study investigates whether steel fiber-reinforced concrete (SFRC) without carbon additives can provide shrinkage resistance and stable self-sensing under fluctuating temperature and humidity. Fractional change in resistance (FCR) and environmental logging are monitored for 72 hours. Finite element model (FEM) was calibrated to real-time boundary conditions. FCR increases steadily without drift, R2 > 0.90. This suggests irreversible densification, not reversible moisture conductivity. Shrinkage strains range from 200 µε to 750 µε. Temperature explained 73.3% and 69.8% of shrinkage variance, while humidity explained 65.5% and 59.7%. R2 values are descriptive, as variables are correlated. FEM links a slower FCR increase rate at 10-40 hours to tensile stress that slows surface densification but keeps the conductive network. SEM shows steel fibers bridge 8-12 μm microcracks and promote dense C-S-H gel. This suggests SFRC has potential as carbon-free self-sensing material for hydration and environmental monitoring in laboratory conditions.