In addition to chloride induced corrosion, the other commonly occurring type of rebar corrosion in reinforced concrete structures is that induced by the ingress of atmospheric carbon dioxide into concrete, commonly referred to as ‘carbonation induced corrosion’. This paper presents a new approach for detecting the onset and quantifying the level of carbonation induced rebar corrosion. The approach is based on the changes in the mechanical impedance parameters acquired using the electro-mechanical coupling of a piezoelectric lead zirconate titanate (PZT) ceramic patch bonded to the surface of the rebar. The approach is non-destructive and is demonstrated though accelerated tests on reinforced concrete specimens subjected to controlled carbon dioxide exposure for a period spanning over 230 days. The equivalent stiffness parameter, extracted from the frequency response of the admittance signatures of the PZT patch, is found to increase with penetration of carbon dioxide inside the surface and the consequent carbonation, an observation that is correlated with phenolphthalein staining. After the onset of rebar corrosion, the equivalent stiffness parameter exhibited a reduction in magnitude over time, providing a clear indication of the occurrence of corrosion and the results are correlated with scanning electron microscope images and Raman spectroscopy measurements. The average rate of corrosion is determined using the equivalent mass parameter. The use of PZT ceramic transducers, therefore, provides an alternate and effective technique for diagnosis of carbonation induced rebar corrosion initiation and progression in reinforced concrete structures non-destructively

Corrosion of steel reinforcement is one of the main causes of damage and premature failure of reinforced concrete structures, inflicting enormous costs for inspection, maintenance, restoration, and replacement of the infrastructure worldwide. Conventional approaches for detecting corrosion are based on electrochemical techniques such as half-cell potential, impedance spectroscopy, and linear polarization. These techniques are affected by a number of factors and require direct contact with concrete/steel interface. To overcome difficulties with conventional techniques, a new corrosion assessment approach based on the electro-mechanical impedance technique is presented in this article. This article presents results from a series of accelerated corrosion tests performed on rebars embedded in concrete cubes, wherein measurements are made using piezoceramic (lead zirconate titanate) patches surface bonded on rebars via the electro-mechanical impedance technique. The equivalent structural parameters extracted out from the admittance signatures of the lead zirconate titanate patch are calibrated against the level of corrosion based on which a new corrosion assessment model is proposed. The experimental results indicate that the equivalent parameters are effective in detecting and quantifying the corrosion in a realistic manner.

Rebar corrosion has become a very common cause of degradation in the reinforced concrete structures. It is most frequently the result of the chloride-induced breakdown of the passive film formed in the highly alkaline environment. This article presents a comparison of the sensing capabilities of surface bonded and embedded piezoceramic (lead zirconate titanate) patches in diagnosing chloride-induced corrosion for reinforced concrete structures. Experiments are conducted with lead zirconate titanate patches surface bonded on rebar as well as embedded in the vicinity of the rebar inside concrete to compare the sensitivity of the two. Accelerated corrosion tests are performed on reinforced concrete specimens, and a comparison of the statistical index and the equivalent parameters is done for the two types of sensor configurations. The experimental results indicate that the embedded sensor is very sensitive in capturing the changes occurring in the concrete during chloride ingress. However, when the passive film is damaged, thereby initiating corrosion, their sensing ability is reduced. At this point, the lead zirconate titanate patch surface bonded on the rebar is more effective. Overall comparison of experimental results shows that both sensor types can complement each other for an effective detection and monitoring of rebar corrosion.