Effect of micro-cracking on the electrical and self-sensing properties of an engineered cementitious composite under tensile straining

The piezo-resistive response of a relatively mature engineered cementitious composite (ECC) under tensile straining is investigated and compared with previous studies. In this work, tensile tests were performed on four dog-bone shaped ECC samples and during the loading process, electrical impedance measurements were undertaken over the frequency range 100Hz-1MHz to identify the bulk resistance (hence accurate evaluation of resistivity). At the same time, digital images of the front face of the dog-bone samples were recorded throughout the entire loading process to enable detailed crack width analysis to be taken after testing and to monitor micro-crack formation during testing, using the digital image correlation. It is shown that tensile straining resulted in an overall increase in impedance, but retained a similar overall profile with a weakly developed spur evident at the low-frequency side of the impedance spectrum and a circular arc at the high-frequency side. It is also shown that the fractional change in resistivity increases nonlinearly with strain and is related to the nature of micro-crack formation. Published values for fractional change in resistivity and its relation with strain were found to be in a large scatter and in this study, attention is therefore focused on the crack width distribution during loading.