| Summary: | 碩士 === 國立屏東科技大學 === 土木工程系碩士班 === 88 === The Ultrasonic-pulse methods have been used to detect the voids and cracks in concrete for several decades. The waves generated by the ultrasonic-pulse include P-waves, S-waves and R-waves. However, the distinguish between these waves is less concerned in the literatures of the methods. Instead, the waves measured were assumed as the P-waves and gave an error prediction very often.
This paper first applies the theory of elastic stress waves to analyze the behavior of these three waves in concrete. Then, set up an arrangement of accelerometers connected to a high-resolution of oscilloscope when performing a surface measurement on concrete. The velocities of P-wave and the R-wave were estimated by reading the responses of the waves in time domain. As a similar arrangement, it is used to predict the depths of the cracks in concrete.
From the results by using the ultrasonic-pulse method with a system of accelerometers and oscilloscope, a direct measurement using the ultrasonic apparatus gives a good agreement with the estimated P-wave velocity. The Depth of the cracks measured form 2cm to 20cm deep is very close to the actual depths
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