Study On Mechanism Of Ultrasonic Propagation In Concrete And Method Of Detecting Grouting Quality In Pre-stressed Tendon Ducts

More recently, post-tensioning pre-stressed concrete bridges have been widely used in the highway construction. In our country, more than95%new bridges are pre-stressed concrete bridges, which mainly depend on the pre-stressed tendon duct. However, non-destructive testing (NDT) technique of detecting the grouting quality in pre-stressed tendon ducts is a difficult problem in engineering field. Based on summarizing previous research, we develop a new phased array ultrasonic echo method to detect the grouting quality in tendon ducts.In order to solve the testing problem, we have to answer the following five questions:First, what kind of method can be used for detection? Second, what are the mainly influence factors in the detection result, and how to overcome these difficulties? Third, how to improve the signal to noise ratio and resolution of detecting results? Fourth, how to carry out the detection? Fifth, how to analyze the test results in qualitatively and quantitatively. We will try to answer the above five questions through theoretical analysis, real engineering detection and numerical simulation in this paper. Firstly, based on the previous result and our detecting test, we found the ultrasonic echo is the best way to do detection by comparing the advantages and disadvantages between radar, impact echo, ultrasonic transmission wave and ultrasonic echo wave. Secondly, in order to study ultrasonic propagation and attenuation characteristics in concrete, numerical concrete models were established based on the microstructure. Ultrasonic propagation in concrete was simulated by viscoelastic acoustic wave equation. We have analysis the attenuation, causing by aggregate, pores and reinforced in this ultrasonic propagation within different models of different parameters. And then, we quantitatively calculated the decay characteristics of ultrasonic amplitude and frequency and qualitatively analyze the interference from identifying the grouting defects in the above materials. At last, some suggestions were shown to reduce the interference. Thirdly, according to the characteristics of phased array and tendon ducts, we proposaled the phased array sources method for emitting directional ultrasonic and gather ultrasonic energy to the tendon ducts, which can greatly improve the effective signal to noise ratio (SNR), and highlight the abnormal reflection signals from voids and other abnormal body. We quantitatively calculated the enhancing ability on SNR of phased array by comparing with single source and qualitatively analyzed the improvement on resolution, respectively. Fourthly, We found this kind of detecting method cannot show a full exploration, only a corner of the entire defect, no matter where the detection location is in any angle. Therefore, the multi-angle imaging method was presented. It can show the comprehensive tomography in the whole defect using emitting and receiving ultrasonic waves at different locations. And a new method was proposed by using combined sources. It can rapidly and qualitatively judge the grouting density. Fifthly, the improved virtual dynamic focusing method was used for visibility the grouting defects, in the part of quantitative calculation of the defects. In order to optimize the hardware design of instrument, we employ the delay superposition method to replace the phased array for emitting ultrasonic. Finally, we analyzed the testing resolution and error in virtual dynamic focusing imaging.These numerical simulation and analysis results show that the phased array ultrasonic echo method can solve the NDT problems of detecting the grouting quality in tendon ducts and the detection resolution can reach10mm. This kind of test method is easy to implement with high efficiency. We have90pictures,4tables,146references totally in this paper.