Self-sensing capability of ultra-high performance fiber-reinforced concrete with multiwalled carbon nanotubes

This study aims to investigate the self-sensing capability of ultra-high performance fiber-reinforced concrete (UHPFRC) enhanced with multiwalled carbon nanotubes (MWCNTs) under varying conditions. Several experiments are conducted to clarify the self-sensing properties of UHPFRC with MWCNTs, including cyclic tests of miniaturized UHPFRC sensors and flexural tests of beam specimens with UHPFRC sensor. In the initial phase, experiments are performed to clarify the optimized mix proportion with superior self-sensing capability. The incorporation rates of conductive materials, such as steel fibers (0%, 1%, and 2%) and multiwalled carbon nanotubes (0.1 wt% and 0.5 wt%), are set as the main test variables. The strain and fractional change in the resistance (FCR) of dog-bone specimens under loading are measured, and the gauge factor (GF) of each mix proportion is derived. Miniature UHPFRC sensors are fabricated to have the highest GF of 23.8 and the cross-sections of 30×40mm² and 20×60mm², and their damage sensing performance are investigated through the electrode-configuration methods (wire and plate). The results indicate that when the cross-sectional aspect ratio is high and a copper plate is used as the electrode, the electrical resistance changes more sensitively. Beam specimens are fabricated to validate the applicability of the UHPFRC sensor, and UHPFRC sensors with superior damage-estimation performance are embedded in the tension side of the beam specimens to perform a flexural test. In addition, empirical equations are proposed to estimate the tensile strain of the beam specimens, based on the strain measured using the strain gauge attached to the concrete surface on the tension side and the FCR measured using the UHPFRC sensor, with determination coefficients greater than 0.84.