Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors

This study presents an experimental effort for the damage assessment of concrete reinforcing bars using bonded piezoelectric transducers and the implementation of an integration analytical approach based on the electromechanical admittance method. Tests are performed in (i) single steel reinforcing bars with predefined and artificially induced damages corresponding to two different damage states and (ii) steel reinforcing bars embedded in typical large scale reinforced concrete beams subjected to flexural load at two different loading levels (before and after yielding) that inevitably cause two different damage levels. The damage of the embedded steel bars in the concrete beams after yielding is the result of excessive elongation of the bars due to yielding caused by flexural deformation of the beams. Test measurements of healthy and damaged steel bars and reinforced concrete beams have been conducted using the developed monitoring system. The experimental program comprises data acquisition of current intensity curves for healthy and damaged bars as detected by the test instrumentation and implementation of the adopted admittance-based procedure to evaluate damages at different levels. It can be concluded that the sensitivity of the piezoelectric transducers greatly depends on the selection of the excitation frequencies. Admittance signatures showed a clear gradation of the examined damage levels. The experimental results provide cogent evidence that piezoelectric lead zirconate titanate transducers are sensitive to damage detection in concrete and in steel reinforcing bars from an early stage of the performed tests. Thus, the use of these sensors for monitoring and detecting concrete cracking and steel yielding by employing the electromechanical admittance approach can be considered as a highly promising non-destructive structural health monitoring method.