Identifying voids in plastic ducts in post-tensioning prestressed concrete members by resonant frequency of impact–echo, SIBIE and tomography

A series of standard concrete beams with plastic P-T tendon ducts were tested at the University of Edinburgh using a range of NDT techniques including impact–echo (I–E), stack imaging of spectral amplitudes based on the impact–echo (SIBIE) and ultrasonic tomography. The findings were confirmed by comparison with earlier experiments undertaken using GPR. It has been argued that I–E cannot detect voids in plastic post-tensioned ducts readily. However it has been shown that whilst I–E is less effective on plastic ducts, the SIBIE analysis is more certain. This technique is easier to use than ultrasonic tomography and gives a credible evaluation. The paper goes on to analyse the above tests on a number of beams with confirmation for ultrasonic tomography and GPR.