Experimental and numerical study on detection of sleeve grouting defect with impact-echo method

Grouted sleeve connections are widely used for vertical connections in precast concrete shear walls. Grouting defect is unavoidable in construction and may affect the performance of the joint in service. A two-step research was carried out to investigate the effectiveness of impact-echo method in the detection of grouting defects in sleeves. First, a mechanistic analysis of the differences in the propagation paths of impact stress waves in grout-compact sleeve concrete assemblies and grout-deficient sleeve concrete assemblies was carried out. Second, finite element models of the assemblies with different sleeve arrangements were established, and the FFT decomposition of the impact-echo signals was carried out with the impact point and reception point spacing, impact hammer diameter, sleeves position and thickness of the assemblies as variable groups. At the same time, the difference in thickness frequencies of grout-compact and grout-deficient assemblies was discussed. Results indicate that the presence of grouting defects can be effectively detected by impact hammers of different diameters for centrally arranged single sleeves, making qualitative analysis of grouting defects possible. For side-sleeve and double-sleeve specimens, there is uncertainty in the detection of grouting defects and therefore the impact-echo method needs further study. Furthermore, an amplitude discrimination method for defect location in double-sleeve specimens is proposed. The findings of this study can provide a reference for quality inspection of grouting sleeve connection.