Improved nondestructive sensor for field-friendly measurement of total flux leakage to detect corrosion damage to steel wires in concrete structures

This study introduces the M8 sensor, an improved non-destructive sensor designed to detect cross-sectional losses of steel wires. The ‘M’ in M8 denotes ‘magnet’. Developed as an alternative to the previously used solenoid sensor – which required labour-intensive field winding on tendons or cables – the M8 sensor offers enhanced workability and testing reproducibility. Operating on the same principle as the solenoid sensor, the M8 sensor uses primary coils consisting of eight bar-shaped electromagnets to generate magnetic flux within the steel wires, while a secondary coil measures the total magnetic flux. Variations in the total magnetic flux along the wire length enable the identification of any cross-sectional loss. Numerical simulations were performed to investigate the magnetic flux density distributions in the M8 and solenoid sensors. The results indicated equivalent distributions in both sensors. This implies that the M8 sensor can operate on the same principle. Experimental demonstrations of the M8 and solenoid sensors indicated that the M8 sensor successfully detected a 6.7% cross-sectional loss in the tendon. This confirmed the comparable performance of the M8 and solenoid sensors.