Automated ultrasonic scanning system for three-dimensional SAFT imaging of concrete elements using an electronically switched transducer array

Ultrasonic imaging is well suited for non-destructive detection and localisation of built-in parts and flaws in concrete elements. In order to effectively perform the large number of measurements needed for volume mapping, an automated ultrasonic measurement system for three-dimensional imaging of concrete elements has been developed. The system comprises an ultrasonic instrument, a three-axis mechanical scanner covering an area of 1,00 m × 0,80 m, and control and imaging software. Three-dimensional SAFT (Synthetic Aperture Focusing Technique) reconstructions built from two-dimensional slices are available directly after the measurement. The system can be operated with different transducers and coupling options. To speed up measurement, a linear transducer array was developed consisting of 48 dry-coupled transducers in 16 groups. The transducers are electronically switched to replace mechanical movement in one scan direction by the electronic shift of a virtual transducer, achieving a speed improvement by a factor of 10. The contribution summarises ultrasonic wave propagation in concrete, explains the imaging system, and gives application examples measured at test specimens.