Experimental Study On Nonlinear Ultrasonic Testing Of Duct Grouting Of Prestressed Concrete Beams

In prestressed concrete structures,pre-stressed reinforcement corrosion is easily caused by inadequate pore grouting,which leads to the lack of stability and durability of the structure and causes safety hazards.Nowadays,the detection technology for the fullness of prestressed beam duct grouting is not perfect.The existing ultrasonic nondestructive detection technology mainly uses the change of linear parameters such as sound velocity and amplitude to reflect the compactness of grouting quality.However,due to the possibility of small defects in the duct grouting process,these linear parameters are not sensitive to the detection of small defects,which makes the linear ultrasonic method have certain limitations.Therefore,this paper uses the nonlinear ultrasonic method to detect the small defects in the quality of duct grouting,as an attempt to provide a reference method for the detection of duct grouting in prestressed concrete beams.In this paper,the relationship between the nonlinear ultrasonic parameters and the minor defects caused by slurry quality and insufficient holding time is studied by taking the concrete beam specimens with preset bellows and without bellows as the main research objects.The main work and achievements are as follows:(1)In order to lead to the study of nonlinear ultrasonic method in this paper,the causes and types of pre-stressed concrete pore grouting defects are summarized,and the principle and applicability of various non-destructive testing methods for pore grouting defects are summarized.(2)In order to study whether the nonlinear coefficient is affected by the setting of the bellows,the paper analyzes the ratio of the second-order harmonic amplitude to the square of the first-order harmonic amplitude generated by the beam specimen emitting high frequency It is the non-linear coefficient to detect the relevant parameter information of the grouting micro-defects of the beam specimen.The influence degree of the bellows on the nonlinear coefficient is determined.(3)In order to study the variation of nonlinear parameters with the decrease of slurry quality and the lack of pressure stabilization time,based on the nonlinear ultrasonic detection theory,the different working conditions with the change of mass and pressure stabilization time are preset,and the variation of nonlinear coefficient under different working conditions is analyzed to characterize the micro defects caused by different working conditions.The results show that with the increase of micro-defects,the corresponding nonlinear coefficient will gradually increase,and it is feasible to identify micro-defects by the change degree of nonlinear coefficient.(4)In order to compare the methods,this paper also uses the classical linear ultrasonic method to detect the model beam specimens,and obtains the eigenvalues of the main linear parameters of the ultrasonic time,amplitude and wave velocity.By comparing the test sensitivity of the relevant parameters,it is shown that the variation range of the parameter eigenvalues of the classical linear ultrasonic method is not as large as that of the nonlinear ultrasonic method,and the nonlinear ultrasonic method can better identify the micro defects caused by the reduction of slurry quality and the insufficient holding time than the linear ultrasonic method.