Application of the Phase Spectrum of Impact Echo in the Detection of Grouting Defects in the Tendon Ducts

Abstract

The impact-echo method is widely used to detect grouting defects within prestressed concrete tendon ducts. However, when the distance from the rebar to the test surface was half the depth from the defect to the test surface, the amplitude spectrum of the conventional fast Fourier transform failed to distinguish between internal defects in tendon ducts and external rebar. To overcome this challenge, in this paper, the phase spectrum and amplitude spectrum were combined to identify the internal defects and external rebar of the tendon ducts. First, the amplitude spectrum was used to determine the depth of defects and rebar, and then the phase spectrum was used to further determine the category of the reflected interface (defect interface or rebar interface). The feasibility of the method was verified by model tests and numerical simulations. Afterward, the effects of impact duration, sampling time, the size of defect, duct thickness, rebar, and defect burial depth on the phase of the impact echo were analyzed. The results show that the proposed method can identify the internal defects in the tendon ducts and rebars very well.