The electro-mechanical tensile properties of an engineered cementitious composite

The influence of ongoing cement hydration and multiple micro-crack formation on the electrical impedance of an engineered cementitious composite (ECC) is presented. Impedance measurements are obtained over the frequency range 20Hz-1MHz and displayed in Nyquist format; in addition, the permittivity and conductivity were de-embedded from the measured impedance and presented in both the time and frequency domains to elucidate the nature of conduction and polarization processes. It was shown that over the 90 d curing period, the ECC displays a classic impedance response. Both conductivity and relative permittivity are shown to be frequency dependent due to bulk relaxation processes operative within the composite. Tensile straining was shown to result in a detectable change in the impedance response, but retains a similar overall profile. When presented in the frequency domain, a downward displacement in both conductivity and relative permittivity profiles was evident with increasing tensile strain. It is shown that the relative permittivity at the high-frequency end could be exploited as a potentially useful indicator for strain/damage detection. The influence of micro-cracking on the piezo-resistive response of the composite is discussed based on crack patterns obtained from both visual observations and digital image correlation.