Non-destructive Inspection Of Concrete Defects Using Elastic Reverse Time Migration Method Based On Vector Wavefield Separation

Due to the advantages of convenient construction and reliable strength,complex concrete structures such as prefabricated concrete structure and concrete-filled steel tube structure have developed rapidly in recent years and gradually become the mainstream structure form of modern architecture.However,due to the complexity of the structure,it is also more difficult to detect the construction quality.At present,the ultrasonic testing equipment used in the market mostly adopts TFM algorithm,which is difficult to meet the standard of engineering testing.In this paper,a concrete defect detection method based on elastic wave field separation reverse time migration imaging is proposed for the defects of prefabricated sleeve grouting compaction,cavity and peeling of concrete filled steel tube.Through the migration imaging processing of the full matrix capture array collected by the ultrasonic phased array,the reconstruction images of the internal defects of complex concrete structures are obtained,and the high resolution and visual detection of concrete defects are realized.In this paper,the advantages and disadvantages of traditional ultrasound imaging algorithms are described,and the necessity of wavefield separation is illustrated.A random medium model of concrete was established to study the effects of coarse and fine aggregate in concrete on ultrasonic propagation,and a numerical simulation experiment was carried out based on the optimized ultrasonic phased array layout.A total of four groups of simulation experiments are set up,which are prefabricated concrete grouting sleeve defect model,full grouting model,concrete-filled steel tube cavity model and concrete-filled steel tube peeling defect model.In order to verify the advantages of the proposed algorithm,the experimental results are compared with the imaging results of the traditional reverse time migration(RTM)algorithm.The simulation results show that the proposed algorithm can significantly suppress the crosstalk noise and greatly improve the resolution of reconstructed images.In addition,the traditional RTM algorithm is not effective for defect imaging of concrete-filled steel tubular peeling model,while the method proposed in this paper can identify the peeling boundary better.In order to further verify the effectiveness of the proposed algorithm,laboratory model tests were carried out,and two model test blocks were cast,namely the prefabricated sleeve and the concrete-filled steel tube test blocks.Among them,the prefabricated sleeve model contains two connecting sleeves: full grouting and no grouting,and the concrete-filled steel tube test block contains a cavity defect.The full matrix data is acquired by the ultrasonic phased array system,and the image reconstruction results of the full focus imaging algorithm and the proposed algorithm are compared respectively.The experimental results show that the TFM algorithm can only image the reflection at the top of the sleeve,and the method proposed in this paper can effectively distinguish the non-grouted sleeve from the fully grouted sleeve,and can effectively improve the resolution of the imaging of the cavity of the CFST structure to meet the requirements of engineering detection.