Unified AC-based framework for self-sensing UHPFRC: Effects of fiber length and electrode geometry under tension and compression

Abstract

Smart ultra-high-performance fiber-reinforced concrete (S-UHPFRC) exhibits strong potential for self-sensing and structural health monitoring (SHM); however, its electromechanical behavior is strongly influenced by the fiber characteristics and electrode configuration. The coupled effects of the fiber length and electrode geometry, particularly under both compression and tension, remain insufficiently understood, limiting the translation of laboratory findings into practical SHM applications. To address this gap, this study systematically evaluates the influence of three fiber lengths (6, 13, and 19.5 mm) and three embedded electrode geometries (I-, U-, and W-type, comprising one, two, and three embedded legs, respectively) on the electromechanical response of S-UHPFRC under uniaxial compression and tension using alternating current measurements. The fiber length significantly affects both the direction and stability of the sensing response, exhibiting opposite trends in compression and tension. Under compression, mixtures with shorter fibers produce the largest fractional change in electrical resistance (FCR), with CU-06 reaching −7.67 % and a low variability of 0.99 % at 139.9 MPa. In contrast, longer fibers enhance tensile stress sensitivity, with TU-19 achieving an FCR of 29.78 %. Overall, the results highlight that coordinated optimization of fiber length and electrode geometry is essential for achieving reliable, high-performance self-sensing in S-UHPFRC and provide practical guidance for its implementation in large-scale SHM systems. Among the three electrode configurations, the U-type electrode consistently exhibited the most reliable and stable sensing performance under both loading conditions, clearly outperforming the other configurations.