Localized damage detection using UHPFRC sensors with carbon nanotubes: Experimental study and applications

This study aims to evaluate the self-sensing capability of ultra-high performance fiber-reinforced concrete (UHPFRC) sensors incorporating steel fibers (SF) and carbon nanotubes (CNT). The primary objective is to assess the effectiveness of UHPFRC sensors as strain-detecting devices, focusing on their sensitivity, accuracy, and applicability to structural elements. UHPFRC sensors were fabricated with SF and CNT incorporation ratios of 2 % and 0.5 wt%, respectively, and their self-sensing performance was examined under cyclic loading conditions. To derive the optimal UHPFRC sensor, the gauge factor (GF) of the sensors was calculated by analyzing the relationship between the fractional change in resistance (FCR) and the strain of the UHPFRC sensor. Furthermore, a practical application of the optimal UHPFRC sensor was conducted by embedding the sensor in the negative moment region of beam–column joint specimens. Both monotonic and cyclic loadings were applied to validate the sensor's performance in structural members. The strains measured by the UHPFRC sensors were compared with those from conventional strain gauges attached to the concrete surface and reinforcement bars. The results demonstrated that UHPFRC sensors can accurately detect tensile strains in the beam–column joint, even under significant plastic deformation caused by monotonic loading. Additionally, during cyclic loading, the sensors effectively measured strain increases corresponding to rising drift ratios, although a slight overestimation of residual strain was observed. These findings confirm the potential of UHPFRC sensors as reliable and durable strain-detecting devices for structural health monitoring.