A Study of PZT Sensors for Crack Detection in Reinforced Concrete

Over the past two decades structural health monitoring (SHM) of civil infrastructure using piezoceramic materials has received growing attention. The majority of studies carried out have focused on lead zirconate titanate (PZT). An important factor which influences the performance of these sensors is the distance from the defect, which is often a crack. Here we present the performance of PZT disc shaped sensors for SHM employing the electro-mechanical impedance (EMI) approach. The sensors were embedded in small scale reinforced concrete beams loaded in three-point bending and impedance measurements of the sensors were taken at various strain levels during the loading cycle. Sensor performance was assessed in relation to the distance from the cracks formed. Damage quantification was determined using the root mean square deviation (RMSD) index. The results indicate that the performance of the PZT material tested in this loading regime was significantly affected by the distance from the cracks. Differences in the range of 10mm were detected. The results demonstrate that when the distance from the crack is approximately 20mm the damage can be detected at an early stage and the damage level can be determined with very high precision. The research reported is part of a much wider programme of work aimed at developing a smart concrete system capable of self-sensing, diagnosing and healing cracks, and other forms of damage, without any need for human intervention.