Ultrasonic guided waves for inspection of grouted tendons and bolts

There is currently a need to improve the nondestructive testing techniques that are used to inspect grouted steel reinforcing tendons, anchors, and rock bolts for corrosion and fracture. A method of inspection using guided ultrasonic waves has been proposed, which uses a pulse-echo technique carried out from the free end of the structure. The maximum inspection range is determined by the amount of attenuation that the wave experiences as a result of leakage into the embedding material and material losses. However, previous work has identified high frequency modes that have low attenuation and so increase the inspection range. Research has been carried out with a focus on the inspection of the posttensioning tendons used to reinforce concrete. The research presented in this paper uses experimental techniques to measure the attenuation in short lengths of grouted tendons, to evaluate the reflection coefficient of the modes from different geometry breaks, and to assess the impact of tendon curvature. The outcome of this research shows that the inspection range for tendons is limited, but the outlook for the inspection of the larger diameter grouted bolts and rebars that are used in the construction industry is promising. Considerable success has already been achieved in the testing of epoxy bonded rock bolts using this method.