###### Abstract
The embedded sensor method is particularly well-suited for in-situ applications, where the sleeves are already embedded within the precast concrete elements [19; 23]. In such scenarios, the lack of access to the exposed steel reinforcement ends prevents the direct application of the impact-echo technique. Conversely, the impact-echo method can provide more detailed information about the internal condition of the grouted sleeve, including the presence of voids or defects, but it requires access to the exposed steel reinforcement ends for the excitation of the stress waves [24]. To overcome the limitations of the individual testing methods and leverage their respective advantages, a collaborative sensing approach can be developed by exploring the correlation between the vibration energy values obtained from the embedded sensor method and the density information derived from the impact-echo technique [25; 26]. By establishing a relationship between these two parameters, it becomes possible to enhance the accuracy and reliability of the grouting quality assessment for sleeve connections, particularly in situations where the impact-echo technique cannot be directly applied. This study aimed to investigate the relationship between the vibration energy values measured by the embedded sensor method and the density information obtained from the impact-echo technique, and to establish a method for the collaborative sensing of grouting filling degree in sleeve connections. The research workflow is presented in Figure 1. The performance of the embedded sensor method in assessing the grout filling degree of sleeve connections under varying levels of grout filling was analyzed. The effectiveness of the impact-echo technique in determining the grout filling degree of sleeve connections was evaluated, and a correlation between the detected density and the actual grout filling degree was established. A collaborative sensing approach was developed by exploring the relationship between the vibration energy values from the embedded sensor method and the density information from the impact-echo technique to enhance the accuracy of grouting quality assessment for sleeve connections. Finally, the proposed collaborative sensing approach was validated through field demonstration and provided practical guidelines for its implementation in real-world precast concrete construction projects. The structure of this paper is organized as follows. Section 2 presents the materials and methods used in the study, including the detailed procedures for the embedded sensor method and the impact-echo technique, as well as the design of the experimental models. Section 3 discusses the results obtained from the laboratory experiments and the field demonstration, and analyzes the correlation between the vibration energy values and the grout filling degree. Finally, Section 4 summarizes the key findings of the study and provides recommendations for future research and practical applications. The research presented in this paper contributes to the body of knowledge on the quality assessment of grouted sleeve connections in precast concrete structures. By developing a collaborative sensing approach that combines the strengths of the embedded sensor method and the impact-echo technique, the study offers a more comprehensive and reliable solution for evaluating the grout filling degree, which is critical for ensuring the structural integrity and safety of precast concrete buildings. The findings of this research can be valuable for practitioners, researchers, and policymakers in the precast concrete industry, helping to improve the quality control and construction practices for precast concrete structures.