Abstract
In this work, non-linear ultrasonic wave techniques have been used to detect the onset of micro-cracking due to steel corrosion in model reinforced concrete elements. The specimens were of prismatic shape with a single steel rebar. The corrosion was forced by admixing an appropriate amount of sodium chloride at the moment of preparing the concrete mix, and by the application of an electric field, using a constant current density power source, and making the steel rebar work as the anode, and an external counter-electrode as the cathode. The preliminary results indicate that the onset of cracking seems to be accompanied by the appearance of higher-harmonic generation at the output signal (harmonic distortion), when the system is excited by the means of an ultrasound wave with a burst central frequency. Other phenomena related to the micro-cracks induced by corrosion, such is the parametric generation with respect to the fundamental amplitude, have not been observed until now.
Highlights
The corrosion of steel is one of the main mechanisms limiting the service life of reinforced and pre-stressed concrete structures, both in buildings and civil infrastructure [1]
The results indicate a good concordance between the experimental and theoretical values, which confirms the validity of assuming that the corrosion of steel before the forced corrosion test is negligible
The preliminary results that are obtained in this work indicate that it is possible to use non-linear ultrasonic techniques for the detection of cracking of model-reinforced cement mortar specimens, due to the corrosion of the embedded steel rebar
Summary
The corrosion of steel is one of the main mechanisms limiting the service life of reinforced and pre-stressed concrete structures, both in buildings and civil infrastructure [1]. Further consequences of the corrosion of embedded steel are the following: loss of bonding between concrete and steel, loss of steel ductility, and loss of the cross-sectional area of steel [5]. These phenomena contribute to the reduction of the serviceability and load-bearing capacity of the structures. There is much interest in developing non-destructive appraisal techniques that are able to provide early warnings for corrosion initiation. These techniques would be very useful for the surveying and inspection of structures in the field of maintenance and repair of constructions affected by reinforcement corrosion.
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