Frequency-dependent Electrical Capacitance and Resistance of Ultra-high Performance Concrete and Their Responses to Compressive Strain

The frequency-dependent electrical properties and strain self-sensing behaviour of ultra-high performance concrete (UHPC) as cement-based stress/strain self-sensing (CBSS) smart materials were investigated in the frequency range from 100 Hz to 300 kHz. By using the electrical parameters of the equivalent electric circuit model, the quantitative relations of capacitance and conductance of CBSS with the measurement frequency were derived. The capacitance and the conductance exhibit power-law type dependence on the measurement frequency. The calculated capacitance values at frequencies beyond 2 kHz and conductance values are consistent with the experimental results. The sweep-frequency test and the fixed-frequency test were performed to examine effects of the excitation frequencies on strain self-sensing properties of CBSS. The fractional change in capacitance (FCC) and resistance (FCR) of CBSS are frequency-dependent in the frequency range from 100 Hz to the f_B, but frequency-independent in the frequency range from the f_B to 300 kHz. The f_A and the f_B are 1.7–4.0 kHz and 11–78 kHz depending on the fiber dosages, respectively. FCC and FCR reach their maximum at the f_A and 100 Hz, respectively. The responses of capacitance and resistance of CBSS to strain show good repeatability during cyclic loading. As the fiber dosage increases, capacitance-based sensitivity to strain increases initially and then decreases at the f_A, and resistance-based sensitivity to strain of CBSS increases with increasing fiber contents.