Electromechanical impedance-based embeddable smart composite for condition-state monitoring

In the present study, an alternating current (AC) based electro-mechanical impedance (EMI) technique was employed to evaluate the performance of smart cementitious composite-based impedance sensor (SCC-iS) over a frequency range, and then was employed as embeddable sensor for monitoring and assessing the health of concrete structure. For this purpose, a method for developing SCC-iS by reinforcing the carboxylic group (COOH-) multi-walled carbon nanotube (COOH-MWCNT) in the cementitious composite matrix is described. The optimal CNT concentration in SCC-iS was obtained based on the AC impedance measurement technique over a specified frequency range. After finding the optimal CNT concentration in SCC-iS, their piezoresistive behaviour (in terms of change in electrical impedance or electrical conductance) was examined using an electro-mechanical impedance measurement approach under uniaxial compressive loading. Finally, the developed sensor is employed as an embedded sensor for damage monitoring of structures under flexural loading. The acquired electrical impedance-and conductance-responses from the SCC-iS were utilized to evaluate the occurrence and progression of damage in real-time. The damage metric and the shift in frequency band were used to quantify the level of damage in the structures. From the experimental study, 0.50 wt% CNT concentration is found to be optimum for developing the efficient SCC-iS. Under the uniaxial compressive loading, the electrical variation in impedance (EVZ) and electrical variation in conductance (EVC) in SCC-iS exhibit excellent correlation with compressive strain and are capable of detecting the damage. The acquired signals from embedded SCC-iS show the effectiveness and sensitivity (in both qualitative and quantitative terms) for damage monitoring of structures; even they are capable of tracing the early-stage damage initiation in concrete structures. The electrical conductance spectra within a specified frequency range show a leftward shift, indicating the degradation in stiffness of concrete structure. Overall, the developed SCC-iS is the first of its kind and is found to be very effective and durable for real-time monitoring of structures, especially in the aggressive environment.

Automated summary

In this study, an AC-based electro-mechanical impedance (EMI) technique was utilized to evaluate the performance of smart cementitious composite-based impedance sensor (SCC-iS) over a frequency range, and then it was employed as an embeddable sensor for real-time monitoring of damage in concrete structures. Experimental results showed that 0.50 wt% CNT concentration is the optimum for developing efficient SCC-iS. Under compressive loading, the electrical variation in impedance (EVZ) and electrical variation in conductance (EVC) in SCC-iS demonstrate correlation with compressive strain and can detect damage effectively.