Abstract
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 230days. 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.
Highlights
Rebar corrosion is widely regarded as the most common cause of deterioration and premature failure of reinforced concrete (RC) structures [1]
No piezoelectric lead zirconate titanate (PZT) patch was attached to the reference sample as this was to be used for destructive testing such as for phenolphthalein test measurements to determine the carbonation depth and imaging analysis
This paper has presented a new approach for monitoring the progression of carbonation and the coupled rebar corrosion in RC structures based on the equivalent stiffness parameter (ESP) and equivalent mass parameter (EMP) parameters extracted from the admittance signatures of PZT patches surface-bonded to the rebars
Summary
Rebar corrosion is widely regarded as the most common cause of deterioration and premature failure of reinforced concrete (RC) structures [1]. Such high frequencies of vibrations are achieved by electrically exciting the PZT patch (in turn bonded to the surface of the structure to be monitored), by means of an impedance analyzer/ inductance capacitance and resistance (LCR) meter Under such external field excitation, the bonded patch induces deformations in the host structure (converse effect), whose response is transferred back to the patch (direct effect) in the form of an admittance signature, consisting of the conductance ‘G’ (real part) and the susceptance ‘B’ (imaginary part). C2 (determined from the signatures of the PZT patch in the ‘free-free’ condition) were introduced by Bhalla and Soh [18] to realistically represent the behaviour of an actual It can be observed from Eq (3) that any damage to the host structure (i.e. any change in mechanical impedance ‘Zs,eff’) will induce a deviation in Y , thereby providing an indication of the damage. The sections describe the identification of structural system based on the values of ‘x’ and ‘y’ and utilization of the ESP for monitoring and quantifying the severity of the structural damage induced by carbonation on rebars embedded in concrete
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