Abstract:

Because of the characteristic of concrete quality detection, it’s necessary to adopt the bending ray in the technique of ultrasonic tomography. A grid model of wave speed distribution is built at first. Then the ultrasonic ray is traced with the shortest path method and the simultaneous iterative reconstruction technique(SIRT) is adopted to image. In order to adjust the algorithm to bending ray, the calculation procedure of SIRT is revised. The iteration in the outer layer is enhanced to do the next inversion of the modified path. To improve the inversion precision, the signal reliability coefficient is established and revised according to the informations such as: ray propagation distance, amplitude attenuation and frequency break, etc. According to this coefficient, the weighted average is calculated when solving the modified value of grid slowness. In order to improve the calculation speed, the grid number is dynamically adjusted; and the shortest path is searched in bi-direction. Through the numerical simulation and field measurement of concrete piles, it is proved that there is an obvious improvement on the calculation accuracy; and its calculation speed can be accepted in the engineering application.

Key words: concrete, bending ray, shortest path, simultaneous iterative reconstruction technique, ultrasonic tomography