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Detection of cracks and casting defects in steel fiber concrete using resonant frequency response

Main aim of this work is to predict steel fiber distribution in fiber reinforced concrete (FRC), e.g. fiber segregation, with impulse excitation method. The method is based on measuring resonant frequencies of vibration in prismatic specimens excited by impact hammer. Prior to testing, specimens are exposed to X- rays in order to validate reliability of test results. Additionally, possible internal cracks and other defects are explored. The test are performed on specimens with different concrete mixtures and different known defects. Two types of acceleration transducers are used to record response signal. By use of discrete Fourier transform, acceleration in time domain is transformed into frequency domain. Further, resonant frequencies are determined as frequency response peaks. From fundamental resonant frequency dynamic modulus of elasticity of FRC is calculated according to standard ASTM C215. From the test result analyses, influence of fiber distribution and some internal defects, such as cracks, voids etc. can be observed. Since this method is non- destructive, same specimens are conducted to four point bending test and standard compression test, in order to obtain static modulus of elasticity

fiber reinforced concrete, resonant frequency, impulse excitation method, dynamic modulus of elasticity

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