Study On The Ultrasonic Wave Field And Detection Method Of Concrete Based On Random Medium

Concrete is a typical random inhomogeneous medium composed of different materials with different physical properties,different geometric shapes,diverse content and proportions,and random spatial distribution,which correspond to the drastic changes of physical properties at the macro level.The typical defect types and occurrence of concrete are various.In addition,the high frequency ultrasonic wave has a short wavelength,which makes the attenuation and scattering by random medium is obvious.As a result,ultrasonic wave field response characteristics of defects are very complex,which limits the application of ultrasonic wave method in the field of non-destructive testing of concrete structures.In this paper,the ultrasonic characteristics of concrete meso-component materials,the corresponding relationship between ultrasonic propagation characteristics and component material parameters,the reconstruction of concrete random aggregate structures model and the ultrasonic field response characteristics of typical defects are systematically studied by means of experimental testing,theoretical analysis and numerical simulation.The following research results are obtained:(1)The acoustic parameters of concrete and its component materials were tested and analyzed,and the variation rules of acoustic impedance parameters and quality factors of cement mortar materials under different water-cement ratios and cement-sand ratios were obtained.The relationship between aggregate size,water-cement ratio,cement-sand ratio,aggregate content and ultrasonic wave velocity of concrete was analyzed.(2)Based on the measured acoustic impedance and quality factor of cement mortar and aggregate,combined with the real concrete random meso aggregate structure,the influences of aggregate particle size,aggregate content,cement mortar velocity and cement mortar quality factors on ultrasonic wave propagation characteristics were quantitatively studied.The effects of random inhomogeneity of concrete on ultrasonic waves with different center frequencies are analyzed from the perspectives of energy and frequency attenuation.The relative importance of scattering and intrinsic absorption is evaluated.(3)An efficient 3D concrete meso aggregate model reconstruction algorithm is proposed.Considering the microstructure of concrete,concrete samples with different aggregate size and different aggregate content were prepared.Based on random process theory,the internal random aggregate structural characteristics of concrete were described and a three-dimensional stochastic gray model of concrete is established.Combined with the digital image processing technology and stochastic optimization reconstruction algorithm,the concrete two-phase model reconstruction is realized.Based on this algorithm,the reconstruction of concrete models with different aggregate sizes,different aggregate contents and different sizes was completed.(4)Based on the reconstructed concrete random aggregate model,the propagation of ultrasonic wave in defective concrete is simulated.The action mechanism of typical defects in ultrasonic field and the propagation path of reflected wave are revealed,and the response characteristics of typical engineering defects in reflected wave field are obtained.By using synthetic aperture focusing technology,the ultrasonic field under random disturbance were imaged and the high-resolution detection of defects by small aperture ultrasonic probe is realized.(5)Ultrasonic pulse-echo test was carries out for concrete cavity defects and the hyperbolic reflection wave of defects in ultrasonic field was obtained.The synthetic aperture focused technology was performed to obtaine the accurate spatial location and size information of the defect.In this paper,there are 82 figures,12 tables and 139 references in this paper.