Piezoelectric cement sensor-based electromechanical impedance technique for the chloride ion content monitoring of hardened concrete

Abstract

A nondestructive testing method using piezoelectric cement sensors (PEC sensors) to monitor the free chloride ion content of hardened concrete by using the electromechanical impedance (EMI) technique is proposed. Piezoelectric cement, a sensing element, is a 0–3 type cement-based piezoelectric composite comprising 50% lead zirconate titanate (PZT) particles. The rapid chloride ion permeability test (RCPT) complies with ASTM C1202 to accelerate the content and penetration of chloride ions in concrete while measuring the electromechanical impedance spectrum of concrete with a PEC sensor. The free chloride ion content in concrete was determined following ASTM C1218. The conductance root-mean-square deviation (GR) was calculated within the effective frequency range to assess chloride ion (Cl) in concrete. The results indicate that the total passed charge, according to the RCPT specification, lies in the linear to nonlinear transition region of the passed charge and free chloride ion content curve. The conductance within the effective frequency monitored with the PEC sensor increases with the free chloride ion content in concrete. The effective frequency band is 1350–2000 kHz. The Cl-GR curve of concrete having an exponential relation is established. After chloride ion penetration in RCPT for about 6 hours, the GR value will be increased sharply. The PEC sensor has the ability to monitor free chloride ion content in concrete, and the conductance RMSD correlates highly with the free chloride ion content. The proposed approach can be used to monitor the free chloride ion content of concrete structures.