Development of non-destructive test of measuring the concrete crack depth

点击翻译按钮获取中文摘要

The main purpose in this study is to estimate the depth and inclination angle of a crack in concrete.1. Magnetic powders were packed into a crack and magnetized with E-form or V-form ferrite core with a pick-up coil centered between the exciting coils. The magnitude and phase of the magnetic flux caused by the core packed with magnetic powders were measured. The experimental results show that the inclination angle could be clearly recognizes, and depth of the crack was determined to be half distance of exciting coil.2. Conductive powders or liquid are packed into a crack and set up the ground plane of aluminum as thin as 2mm. N-type connector is mounted on a ground plane which inner conductor is in contact with conductive powders or liquid in a crack, and ground plane. Monopole antenna is composed of conductive material in a crack and ground plane. Input impedance of the monopole antenna was measured by network analyzer. The length of crack is odd number of quarter wavelength long, when the imaginary part will be zero.That isL = λ/4 = c/(4 × f_0 × √<ε_s> (1)where λ is wavelength , L is the length of crack, c is the velocity of light, f_0 is resonant frequency, and ε_s is relative permittivity.It is therefore possible to estimate the deep crack depth(1〜2m) in terms of the resonance frequencies.