Grout assessment of plastic ducts in prestressed structures with an HHT-based method

This paper introduces the detection of grouting quality in plastic ducts in prestressed concrete structures based on impact-echo (IE) testing with an HHT-based method. This method takes steps to suppress unrelated signals. At first, the thickness frequency of the intact concrete whose thickness is equal to the detected concrete is calculated, then a band pass filter is conducted to filtering uncorrelated frequency component. Secondly, complementary ensemble empirical mode decomposition (CEEMD) is used to decompose the signal to intrinsic mode functions (IMFs). Thirdly, an IMF screening process is conducted on the IMFs to extract the main patterns of vibrations related to grouting. At last, the Hilbert marginal cumulative spectra are set up. This method has been verified by both simulated and laboratory models. The cumulative Hilbert marginal spectra showed that the thickness frequencies decreased gradually with the decreasing of grouting compactness. On-site IE tests verified the feasibility and practicability of the proposed method.