Experimental evaluation of load-induced damage in concrete from distributed microcracks to localized cracking on electro-mechanical impedance response of bonded PZT

The main focus of this paper is monitoring evolution of damage in concrete, from distributed microcracks to localized cracking, under compressive loading using bonded lead zirconate titanate (PZT) patches. Incremental load-induced material damage, from distributed microcracks to localized cracks, is evaluated experimentally using measures of mechanical compliance and surface displacements obtained using a full-field optical technique based on digital image correlation. The relationships between forms of material damage, visual indication of damage, mechanical compliance of the material and resonant mode in the electro-mechanical (EM) impedance measurement of a PZT bonded to a concrete substrate, are investigated. Incipient damage in the form of distributed micro-cracks results in a decrease in the frequency and a change in the amplitude of the resonant peak in the conductance spectrum obtained from EM impedance measurement. Evolution of microcracks produce an increase in substrate compliance and an increase in material damping, which produce consistent changes in EM conductance. Localization of damage in the form of major cracks produces broadening of the resonant peak in the conductance spectrum. Significant variability in the response of the PZT is produced because of the spatial heterogeneity introduced by the crack. The root mean square deviation derived from conductance spectrum centered on the resonant peak indicates trends identical to the changes in the mechanical compliance of the substrate produced by damage.