Grout compactness detection of grouted splice sleeve (GSS) connector based on damping effect induced ultrasonic wave attenuation

As an important connection component for prefabricated concrete (PC) structures, grouted splice sleeve (GSS) connectors are widely employed in building construction. However, effectively detecting grouting defects in GSS connectors remains challenging due to their concealed and inaccessible nature. This paper proposes a novel grouting defect detection method based on damping effect-induced ultrasonic wave attenuation. Based on one degree-of-freedom (DOF) free vibration system, an ultrasonic propagation absorption attenuation model considering the damping effect is built. The result indicates that the response of the model is exponentially decaying. Compared to the empty case, 90% of the ultrasonic energy is dissipated when the ultrasonic waves propagate in a compact GSS. To validate the feasibility of the detection principle, five grouting compactness cases (0%, 28%, 50%, 72%, and 100%) were artificially mimicked and tested. To improve the Signal-to-Noise Ratio (SNR), the time reversal algorithm was applied. The normalized amplitude of the focused signal in the time domain is used as an index to quantitatively reveal the compactness of GSS connectors. Experimental results confirmed that grout material significantly enhances damping effects. In addition, the damping ratios of the GSS connector and the grouting stuffing were experimentally investigated based on the logarithmic decrement of ultrasonic wave. A 2D numerical model verified that groutinduced damping causes exponential ultrasonic attenuation, aligning with theoretical predictions and experimental data. Therefore, the proposed damping effect-induced ultrasonic wave attenuation is viable for grouting compactness detection.