Experimental monitoring of accelerated corrosion damage in a prestressing steel strand using three non-destructive testing methods

The aim of this work was to provide further confirmation of the possible use of three non-destructive methods to detect corrosion-induced damage in prestressing steel strands. To this end, accelerated corrosion tests were conducted on prestressed steel strand while monitoring the consequences of the progressing corrosion process. Nonlinear ultrasonic spectroscopy, the metal magnetic memory method, and acoustic emission were employed. The results demonstrated that all three methods were sensitive to damage in the steel strands caused by corrosion progression. In the case of nonlinear ultrasonic measurements, the results indicated that corrosion-induced damage in the strand was characterised by pronounced nonlinear features in the received signal. In this study, a relative nonlinearity parameter based on harmonic distortion and intermodulation was used to quantify damage in the steel strand. For the metal magnetic memory method, a parameter based on measurements of magnetic field intensity in the form of residual magnetisation on the material surface was applied. The results are presented as magnetograms showing the distribution of magnetic field intensity and its gradient along the steel strand. Variations in magnetic field intensity revealed distinct stress concentration zones correlating with the effects of the advancing corrosion process. Acoustic emission provided continuous information on the degradation process in the corroded steel strand. The evolution of acoustic activity recorded during the tests indicates the presence of several phases associated with crack initiation due to local corrosion by aggressive substances, subsequent crack propagation, and final steel rupture.