Research On Sleeve Grouting Defect Detection Based On Ultrasonic Combined With Acoustic Emission

Grouted sleeve connection has been widely used to connect rebars in prefabricated concrete 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 prefabricated concrete structures.Therefore,it is necessary to explore a reliable and efficient method for the detection of sleeve grouting defects.In this paper,an ultrasonic(UT)combined with acoustic emission(AE)method is proposed to determine and characterize the damage state and damage process of grouted sleeves with different degrees of internal defects under cyclic tensile action.UT detection is performed prior to cyclic tensile testing to evaluate internal defects,and the mechanism of UT detection is comprehensively described.Through numerical simulations and experimental studies,a linear relationship between UT signal energy ratio and sleeve grouting defect rate was established,and the optimal path for UT detection of internal sleeve defects was determined.Using the AE method as a processing monitoring technique during cyclic tensile testing,two damage modes were identified:(i)brittle mode associated with sleeve rebar pullout;and(ii)ductile mode associated with sleeve rebar fracture.At the same time,the AE characteristics of different damage stages and different damage modes were clarified and characterized.For the brittle and ductile damage modes,two and three stages,respectively,appear in the AE activity.UT was used to non-destructively determine the damage state of grouted sleeves,while AE was used to characterize the damage progress of grouted sleeves.Combining UT and AE to characterize the damage state and progress of grouted sleeves,the UT damage index(DI)is proposed and the rejection line for failure of the sleeve mechanical properties is defined.Generally,if the DI is below the rejection line,three stages of damage are observed in AE activity.Damage exhibits more ductile modes,with reinforcement fracture being the primary damage outcome.The bond strength of grouted sleeve connections is not affected by internal defects.On the contrary,once the DI is above the rejection line and the AE activity of the two stages of the damage process dominates,the damage shows more brittleness and reinforcement pull-out is the main damage outcome.The presence of internal defects reduces the bond strength of grouted sleeve joints and negatively affects the safety performance.The proposed combined UT and AE method can provide a reliable and convenient nondestructive assessment of grouted sleeves with internal defects.In addition,it can characterize the damage process of grouted sleeve connections in real time.In order to investigate the influence of grouted sleeve connection nodes on assembled building components,the AE technique was used to monitor the full damage process of assembled grouted sleeve shear walls under reciprocating loads in real time,to identify the damage characteristics at different stages,and to extract the acoustic emission signal features corresponding to them,and to describe the damage destruction behavior of shear walls quantitatively using the features of resolved acoustic emission sources.Finally,the damage sources in the damage process were classified using the cluster analysis method and compared with the AE signal characteristics in the sleeve damage process.The results show that the acoustic emission technique,can quantify the damage process of shear walls and propose prediction and early warning for the damage.