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[Display omitted] • A super-sensitive carbon nanofiber aggregate (SSCNFA) sensor with 0.05% CNFs content has been developed. • The sensor's sensitivity is enhanced due to a well-defined conductive path between CNFs and steel mesh. • SSCNFA can detect forces as low as 0.28 N, making it suitable for stress/strain sensing and damage detection. • The sensor has a wide dynamic range, with any frequency from 1 Hz to 500 kHz available for various applications. A carbon nanofiber aggregate of exceptional sensitivity is developed. Our approach involves the development and utilization of a novel nanobrush structure of carbon nanofiber within the mortar matrix. The high number of nanostructures in the nanobrush, particularly near the electrodes, results in a greater number of nanogaps, leading to a substantial improvement in sensitivity. We are able to detect forces as small as 1 N using this sensor. The carbon nanofiber brush (CNFB) provides a well-defined conductive path for the piezoresistive functioning of the super-sensitive carbon nanofiber aggregate (SSCNFA) with significantly reduced cost. The influence of scanning frequency in impedance is rigorously investigated with alternating current (AC) based on two methods. SSCNFAs are tested in uniaxial compression to determine the highly sensitive face of cube sensor. An SSCNFA (0.05 % CNFs, dense electrodes) and a CNFA (0.5 % CNFs, wide-spaced electrodes) were tested in a sweep-frequency test under parallel compression to compare the super-sensitive performance of the new sensor. The gauge factors at various frequencies were determined. The electrical impedance measured at various frequencies provides versatility to the SSCNFA for stress monitoring. Four fixed-frequency tests were conducted to determine the resolution under uniaxial compression and examine repeatability. [ABSTRACT FROM AUTHOR]

• Ultra-high-performance carbon nanofiber aggreagate is proposed and developed. • The relationship between electrical response and stress–strain response are obtained. • The influence of scaning frequency and loading orientation are investigated. • The proposed sensor has compressive strength of 138 MPa to fit UHPC strength. Ultra-high-performance concrete (UHPC) is rapidly implemented to build robust, durable, and sustainable structures. This study presents the development of a robust self-sensing sensor with the motivation to monitor structures with high-performance construction material, such as UHPC. The ultra-high-performance carbon nanofiber aggregates (UHPCNFAs) are carbon nanofibers (CNFs) and UHPC-based smart aggregates. The newly developed UHPCNFAs are experimentally investigated in uniaxial compression. Sweep-frequency and fixed-frequency tests are adopted in alternating current measurements for determining the electrical behavior of the UHPCNFAs. UHPCNFAs are compressed in parallel and perpendicular loading orientations to understand the difference in the sensor's electrical sensitivity and mechanical behavior in each case. In addition, the robustness of the UHPCFNA is examined to the point of failure in both orientations. The relationship between stress, strain, and electrical impedance variation is established for eight different frequencies. Furthermore, the UHPCNFAs are compressed at a fixed frequency to verify the repeatable behavior. This paper examines the effect of loading orientations on electrical and mechanical response, robustness, and sensitivity of UHPCNFA in a wide range of frequency spectrum to check its suitability in real-time structural health monitoring. [ABSTRACT FROM AUTHOR]

Nanomaterial additives have been broadly used in cement and concrete-based sensors to measure the stress and strain in the structure. Most of the studies focused on measuring the resistivity of sensors with Direct Current (DC) or relatively low-frequency. In this work, the impedance responses of enhanced Carbon Nano-Fiber Aggregates (CNFAs) at different frequencies are rigorously studied and utilized as a tool for real-time structural health monitoring (SHM). The CNFA impedance measurements at different measurement frequencies provide an extra dimension (frequency dimension) to allow the characterization of different phenomena and multimodal measurements simultaneously. First, a comprehensive physical model is established to understand the frequency responses of the CNFA impedance. Second, COMSOL Multiphysics is used to simulate the frequency responses of the CNFA impedance, which provides more insights into the electric field and current density distribution. The impedance of CNFAs decreased with the increased dosage of carbon nanofibers (CNFs). Third, experimental studies are reported in detail. The electrical impedance variation (EZV) of the CNFA in parallel orientation is 151% higher than that of perpendicular orientation at the frequency of 2612 Hz and uniaxial compression stress of 4.65 MPa. The strain-EZV curve obtained from the response spectrum is linear for frequencies ranging from 98 Hz to 463.9 kHz. The strain-EZV curve for 5625 Hz has a linear fit with the gauge factor of 147.78. At 1000 Hz, the CNFA exhibited a repeatable behavior up to 9.35 MPa and detection limit up to the stress of 18.62 MPa. [ABSTRACT FROM AUTHOR]