Ultrasonic Identification Of Concrete Defects Considering Random Distribution Of Aggregates

Ultrasonic technique(UT)is widely used in many engineering fields because of its unique merits(e.g.high accuracy,non-destructive,versatility,portability etc.).Moreover,UT can be used to detect a variety of internal flaws/defects,including cracks,voids,inclusions,and material degradation.Therefore,UT can be successfully used in evaluation of concrete status.However,the high degree of non-homogeneity of concrete impairs the reliability and accuracy of UT detection.And also,UT is a frequency-dependent method.Its resolution and accuracy can be highly influenced by the frequency.Thus,the existence of aggregate in concrete will introduce the uncertainty to the detection,which is often ignored.In this paper,to improve the accuracy and reliability of UT in concrete,the influence of aggregate and frequency were investigated.Through the parametric study,the inherent correlation between the stochastic effect introduced by coarse aggregates and UT signal was revealed based on the combination of experimental and numerical model.Therefore,the UT features for concrete detection are properly selected,which has less influence by aggregate and more sensitive to the internal flaws.The proposed strategy of UT data analysis can provide a guidance for on-site detection in concrete.On the basis of the above studies,the following work was carried out:(1)The relationship between aggregate grain size and ultrasonic wave velocity in concrete was analyzed by preparing concrete specimens with different aggregate sizes.(2)A finite element model of real specimen aggregate distribution was established by combining real concrete fine view aggregate structure with digital image processing technology,enabling efficient reconstruction of concrete models with different aggregate sizes.(3)The influence of aggregate particle size on ultrasonic wave propagation characteristics was quantitatively studied,and the influence of random non-uniformity of concrete on ultrasonic waves of different center frequencies was analyzed from the perspective of energy,wave speed variation,and amplitude.(4)Based on the concrete model of randomly distributed coarse aggregate established by the distribution of real coarse aggregate in concrete,the influence of coarse aggregate on the reliability of UT detection when there are no defects in concrete was studied,and the influence of random distribution of coarse aggregate on the reliability of UT detection in concrete when there were defects in concrete,so as to improve the reliability of ultrasonic detection in concrete.