Up to date, various studies have been conducted using electro-mechanical impedance (EMI) method on concrete, including monitoring the strength development or to find damage in the structure. Since EMI method utilizes a single piezoelectric material to be used as an actuator and a sensor simultaneously, the method has major advantages compared to other non-destructive testing methods. However the method requires a piezoelectric material to be permanently attached or embedded into a structure. Thus when monitoring multiple structures, the method may become quite expensive. In this study, two re-usable EMI methods conducted by researchers Na et al and Tawie et al are overviewed. The idea of re-usable EMI method is still relatively new, resulting in the reduction of monitoring costs since the same piezoelectric material is used as many times as possible, while ensuring better repeatability and reliability in measurements.
In this study, a Non-Destructive Evaluation (NDE) method is introduced for evaluating the effects of FRP
adhesive joint bond strength subjected to various environmental conditions using electromechanical impedance (EMI)
method. The applicability of Fibre Reinforced Plastics (FRP) as a construction material is being globally recognized for
their high stiffness and strength to weight ratio and this method proposes a possibility of detecting any strength loss to
the adhesive bond without damaging the structure, such as FRP joint itself. PZT (Lead-Zirconate-Titanate) patches were
utilized to detect any changes to the bond strength of the FRP adhesive joint exposed to different kinds of environmental
conditions by measuring the electrical admittance of the PZT sensors. In addition, a re-usable technique has been
introduced with a utilization of magnet to allow multiple sensing of specimens with a single sensor. The results show a
possibility of detecting decrease in the bond strength of FRP adhesive using the EMI method.
An impedance-based monitoring technique is used to detect the gradual bonding between steel reinforcing
bar and fresh concrete. The method, which has made significant progress in the fields of structural health
monitoring (SHM) and non-destructive evaluation (NDE), is essentially based on the application of
piezoelectric transducers as collocated sensors and actuators utilizing their direct and converse
piezoelectric effects simultaneously. In this study, a piezoelectric ceramic (PZT) transducer bonded to a
steel rebar was embedded in concrete and the changes in the conductance signature of the transducer were
monitored by exciting it at high frequencies. The monitoring was carried out up to 72 hours to investigate
the influence of setting and initial hardening of concrete.
Various nondestructive monitoring techniques have been explored and developed for
predicting strength gain of concrete. Important issues in the implementation of any
nondestructive techniques are practicality and reliability of measurements. Recently, the
applicability of electro-mechanical impedance (EMI) sensing technique utilizing
piezoelectric materials has been extended to monitoring of concrete strength. This
technique shows a strong correlation between resonant frequency shift of the measured
EMI spectrum of a surface bonded piezo-impedance transducer and compressive strength
of concrete. In the present study, the application of EMI sensing technique for monitoring
strength development of concrete was performed using an impedance analyzer. The effect
of mix proportion of concrete on the EMI spectrum was investigated.