The grouted sleeve connection is one of the most widely used connections for prefabricated buildings (PBs). Usually, its quality can have a significant impact on the safety of the whole PB, especially for the internal flaws that form during sleeve grouting. It is directly related to the mechanical performance and failure behavior of the grouted sleeve. Therefore, it is essential to understand the damage progression of the defective grouted sleeve connection. However, destructive testing is the mainstream measure to evaluate the grout sleeves, which is not applicable for in situ inspection. Therefore, this paper proposes a combined acoustic emission (AE) and ultrasonic testing (UT) method to characterize the damage progress of a grouted sleeve with different degrees of internal flaws under tensile loading. The UT was conducted before loading to evaluate the internal flaws. Additionally, the AE was used as the processing monitoring technique during the tensile testing. Two damage modes were identified: (i) brittle mode associated with the rebar pullout; (ii) ductile mode associated with the rapture of the rebar. The UT energy ratio was selected as the most sensitive feature to the internal flaws, both numerically and experimentally. The AE signatures of different damage phases and different damage modes were determined and characterized. For the brittle and ductile damage modes, two and three phases appeared in the AE activities, respectively. The proposed combined AE and UT method can provide a reliable and convenient nondestructive evaluation of grouted sleeves with internal flaws. Moreover, it can also characterize the damage progress of the grouted sleeve connections in real-time.

Concrete is the most widely used material in civil engineering, which has many advantages in terms of strength, accessibility, and durability. Currently, the high-strength concrete has been used in some projects. However, its failure mode is more complex than the regular concrete. Especially for the loading rate, it may significantly affect the failure mode. Therefore, it is essential to quantify the process of the failure for better application of high-strength concrete with consideration loading rate. Due to many merits of acoustic emission (AE), it has been successfully used for evaluating the progress of concrete damage. Therefore, in this study, the experiments were proposed to correlate the AE with failure mode in the high-strength concrete. As progress of the damage, the AE activities show highly related to the mechanical response.Additionally, the loading rate directly related to the failure mode is also considered. Compared with the regular concrete, the failure of the high-strength concrete shows more brittle behavior. And the phase of AE signals has been changed from obvious three stages to two stages with increase of loading rate, which can be used for further identification of failure mode.

Grouted sleeve connection has been widely used to connect rebars in prefabricated concrete (PC) structures. Due to the complexities of materials and internal configurations, the flaws or defects are inevitable, which may cause the negative impact on the mechanical properties of reinforcement sleeve connection, ultimately leading to the hidden risk in the PC structures. It is challenging to explore a reliable and efficient flaw detection method for the grouting sleeve. In this paper, an active grout defects detection approach for grouted sleeve connectors using UT wave measurement is proposed, where piezoelectric-lead-zirconate-titanate (PZT) transducer are mounted on surface of the sleeve as transmitter and receivers; and experimental study is carried out to validate the feasibility of the proposed method. In order to investigate the effect of grout defects on UT wave measurement, five grouted sleeve specimens with different degrees of the artificial grout defects are designed and analysis on the PZT transducer was used for measurement. By comparing the PZT transducers measurement of different specimens with different grout defects under an identical impulse excitation signal, the grout defect is detected. Experimental results indicate grout defect leads to decrease in PZT transducers measurement UT energy, the relationship between the UT energy ratio and the internal grouting flaws is established: the UT energy decreases with the increment of flaw size. Therefore, the UT method provides a feasible option to evaluate the internal flaws of grouted sleeve connection.