Electrical resistance and capacitance responses of smart ultra-high performance concrete with compressive strain by DC and AC measurements

Electrical properties and strain self-sensing ability of smart ultra-high performance concrete (UHPC) containing different steel fiber concentrations were characterized using DC resistivity, AC resistivity, and capacitance measurements. Four-probe DC resistance measurement and four-probe/ two-probe AC impedance measurement were performed in this study. The resistivity measured by the two-probe AC method is lower than that measured by the four-probe DC method. The magnitude of impedance measured by the four-probe method is close to that measured by the two-probe method. The capacitance of UHPC increases with an increase in fiber dosages, which is mainly related to the interfacial polarization, including the polarization of solid-liquid electrical double layer and fiber/matrix/fiber interfacial polarization. The addition of steel fibers can effectively improve the sensitivity of AC resistance and capacitance variation with strain, but it has less effect on the sensitivity of DC resistance variation with strain, which is due to different strain self-sensing mechanisms. Thus, the sensitivity represented by AC resistance and capacitance is higher than that represented by DC resistance. UHPC with the steel fiber content of 1.5% exhibits high sensitivity and good linear relationship between the fractional change in AC electrical parameters and strain. The results indicate that AC resistance measurement is preferable to be adopted for strain self-sensing using smart UHPC.