Concrete structures in service are often subjected to environmental/operational temperature effects, which change their inherent properties and also inflict a challenge to their extrinsic monitoring systems. Recently, piezoelectric lead zirconate titanate (PZT)-based electromechanical admittance technique has been increasingly growing into an effective tool for concrete structural health monitoring; however, uncertainty in the changes of monitoring signals induced by temperature impact on concrete/PZT sensor would inevitably cause interference to structural damage detection, which adversely hinder its application from laboratory to engineering practice. This article, aiming at exploring the temperature effect on the electromechanical admittance–based concrete damage evaluation, primarily covered a series of theoretical/numerical analysis with rigorously experimental verifications. Three aspects of comparative studies were performed in theoretical/numerical analysis: (1) thermal-dependent parameters were inclusively evaluated in contribution to the electromechanical admittance characteristics via PZT-structure interaction models; (2) three-dimensional finite element analysis in multi-physics coupled field was employed to qualitatively assess the singular temperature effect on the electromechanical admittance behaviors of free-vibrated PZT, surface-bonded PZT/inside-embedded PZT coupled healthy concrete cubes; and (3) depending on the modeling of surface-bonded PZT-/inside-embedded PZT-cracked concrete cube, thermal effect on damage evaluation was addressed via quantification on the electromechanical admittance variations. In the experimental study, rigorous validation tests were carried out on a group of lab-scale concrete cubes, where surface-bonded PZT/inside-embedded PZT transducers were simultaneously employed for electromechanical admittance monitoring in view of thermal difference between concrete surface and its inner part. Correlation coefficient deviation value-based effective frequency shifts algorithm was also employed to compensate the temperature effect. Moreover, temperature effect was further testified on the monitoring of a full-scale shield-tunnel segment structure. Experimental results indicated that temperature triggered different behaviors of electromechanical admittance signatures for surface-bonded PZT/inside-embedded PZT transducers and contaminated the electromechanical admittance responses for damage detection. Structural damage severity level can be disadvantageously amplified by temperature increment even if under the same damage scenarios.

Accelerator/retarder admixtures are often added into concrete to improve its early-age strength, which needs to be effectively monitored during its hardening process. The electromechanical impedance (EMI) technique has validated its effectiveness for concrete hydration monitoring, this study attempted to extend the EMI technique to monitor 28-day age of strength gain in concrete that added with accelerator/retarder admixtures. Two types of new piezoelectric (PZT) transducers namely cement/aluminum embedded PZT (CEP/AEP) were proposed for EMI monitoring. The feasibility of the CEP and AEP was first verified via finite element analysis, where hydration heat effect on the two types of transducers was comparatively evaluated by numerical modeling. In the experiment, CEP/AEP transducers were applied to monitor the strength gain in concrete cubes, where characteristics of EMI signature and its statistical indices including root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD) were analyzed and correlated to strength development in concrete. Monitoring results demonstrated that concrete hydration triggered by retarder/accelerator were successfully captured by EMI signature. RMSD and MAPD indices further indicated that AEP had preferable performance than CEP transducer for monitoring early-age strength gain of concrete, as it could immune from hydration heat effect.