Defect detection for grouting sleeve based on time reversal algorithm and normalized wavelet energy entropy

Grouting defects of grouting sleeve reduce the seismic performance of prefabricated assembled structures and effective detection methods need to be developed. Piezoelectric ceramic transducers are pasted on the surface of the grouting sleeve, and the directly received signals are processed by the time-reversal algorithm to obtain high signal to noise ratio ultrasonic focused signals. Quantitative analysis of the spectral characteristics and energy of the focused signals with different grouting degrees of horizontal and vertical connection sleeves are carried out using the fast Fourier transform and normalized wavelet energy entropy algorithm. The results showed that: compared to the directly received signal, the time-reversed focused signal increases the amplitude by 25. 4 dB, indicating that the focused signal is more suitable for defect detection in the complex connection environment of grouting sleeves. The defect evaluation index based on the normalized wavelet energy entropy method can quantitatively reveal the degree of grouting defects.