Experimental Research On The Damage Of Concrete Based On Nonlinear Ultrasonic Characteristics

Due to the long-term loading, environmental corrosion, material aging, componentbreakage, and other factors, concrete in use gradually produces the accumulation ofdamage inside, which decreases the load capacity and durability of the structure, andreduces the life of the structure. How to effectively predict the damage evolution of theexisting concrete is one of the key issues to be solved in the current concrete works.While the studies on existing concrete injury often use linear theory of ultrasonic fortest and theoretical analysis, which have great limitations, and the research on nonlinearcharacteristics of concrete after the damage is less. Therefore, on the basis of nonlinearwave theory and statistical damage mechanics, by using the ultrasonic testing test of theuniaxial contained concrete which consider the different influence factors’ effect, theultrasonic parameters and sensitive influence factors which correlate well with the stressis got, and the constitutive relations of the concrete damage and ultrasound parametersare analyzed in theory in this dissertation. The main research work and results of thisdissertation are as follows:(1)To study the effects of aggregate ratio, firing frequency, degree of drying on thecorrelation between concrete ultrasound parameters and stress, the paper carries theultrasonic wave tests of the uniaxial loaded concrete with different aggregate ratio,firing frequency and degree of drying. The layout of test program, the using ofinstrument and the determine of the testing parameters are made a detailed presentation.(2)The processing of the acoustic signal is achieved by the Fast Fourier Transformand spectral analysis methods, the ultrasonic parameters which correlate well with thestress are extracted, and the variation of the ultrasonic parameters and the stress areanalyzed, and the acoustic sensitivity parameters which can correctly reflect thevariation are got in this dissertation.(3)Consider the effects of different aggregate ratio, firing frequency and dry degreeon the correlation between concrete ultrasound parameters and stress, the influence ofdifferent factors on the concrete acoustic parameters with the stress is analyzed, the sizeof the various effects which are more sensitive correlation between acoustic parametersand stress are got in this dissertation.(4)From the perspective of meso-damage mechanics, the existing concrete damage model which consider the effect of a single micro-crack propagation effect is analyzed,the contribution of a single micro-cracks in the different stages of the expansion to thestrain is determined, and thus the mechanism of action of micro-cracks expansion isdetermined in this dissertation. On the basis of micro-crack propagation mechanismsand the theory of Weibull statistical damage, the statistical damage constitutive model ofthe concrete is determined, the constitutive relations of concrete damage with velocityand nonlinear ultrasonic parameters are built, and the rationality of the constitutiverelations is analyzed in this dissertation.