###### Abstract  
This study presents a collaborative sensing approach that integrates the pre-embedded sensor method and the impact-echo technique to enhance the accuracy of grout filling quality assessment for precast concrete sleeve connections. The pre-embedded sensor method, which relies on vibration energy attenuation, enables continuous monitoring of the grout filling process; however, its accuracy is limited at low filling degrees, as vibration energy values remain constant at approximately 255 when the filling degree is below 70%. In contrast, the impact-echo technique, based on the principle of impact elastic wave propagation, demonstrates high accuracy in evaluating grout filling degrees across various levels, with reflected waveform amplitude increasing accordingly. This collaborative approach establishes a functional relationship between vibration energy values from the pre-embedded sensor method and grout filling degree, allowing for a comprehensive assessment of grout filling quality. In field demonstrations, the calculated grout filling degree values deviated by less than 5% from the set values. Practical guidelines for implementing the collaborative sensing approach are also provided. The method developed in this study offers a reliable solution for assessing grout filling quality in precast concrete sleeve connections, addressing the limitations of individual testing methods. p 2024 20  
Wet connections, such as the grouted sleeve connection, have become the predominant choice in the majority of precast concrete structures due to their ability to create a continuous load transfer path and achieve a monolithic behavior [4; 8]. In a grouted sleeve connection, the precast members are connected by inserting the reinforcing bars into a sleeve, which is then filled with a cementitious grout material [9; 10]. The quality and completeness of the grout filling within the sleeve directly influence the structural integrity and load-bearing capacity of the connection [7; 11; 12; 13]. Ensuring the quality of grouted sleeve connections is of paramount importance for the overall safety and stability of precast concrete structures. Deficiencies in the grout filling can lead to a reduction in the load-bearing capacity, compromising the structural integrity and potentially jeopardizing the entire building [14]. To address this critical aspect, a comprehensive quality control regime is essential, involving a range of testing methods and equipment to assess the quality of the grouted connections. The quality inspection methods for grouted sleeve connections can be broadly categorized into two groups: destructive testing and non-destructive testing. Destructive testing, such as core sampling and pull-out tests, provides direct information about the grout properties and the integrity of the connection. However, these methods are invasive and can potentially compromise the structural integrity of the precast members. On the other hand, non-destructive testing techniques offer a more viable solution, as they can assess the grout quality without causing any physical damage to the structure [15; 16; 17]. Among the various non-destructive testing methods, the embedded sensor method and the impact-echo technique have gained widespread recognition in the assessment of grouted sleeve connections [18]. The embedded sensor method involves the installation of sensors within the grouting sleeve during the construction phase. After the grouting process is complete, the sensors collect data on the vibration energy, which can be used to evaluate the degree of grout filling and the quality of the connection [19]. The impact-echo technique, on the other hand, utilizes the principle of stress wave propagation to detect defects and density variations within the grouted sleeve [20; 21]. By analyzing the reflected stress waves, the technique can provide insights into the integrity and compactness of the grout filling. Each of these non-destructive testing methods has its own strengths and limitations [22].