An ultrasonic approach for characterising subsurface fractures in concrete

An ultrasonic Rayleigh wave detection method is proposed to determine the geometrical characteristics of subsurface small-scale fractures in concrete. A three-dimensional observation system, including an inclined wedge ultrasonic device, is used to obtain the Rayleigh wave wide-angle data to exhibit the azimuth-dependent scattered wave field. The anisotropic characteristics of Rayleigh wave transmission coefficient are used to determine the distribution range and dip angle of fractures. Fracture models in concrete with different dip angles are designed, and the dip angle is correlated with the degree of attenuation (transmission coefficient) anisotropy. The transmission coefficient characteristics are presented in a random observing system. A focusing approach can be adopted to distinguish the subsurface fracture and to verify the reliability and flexibility of the surface wave approach in practice. The tendencies of experimental results are consistent with patterns obtained from numerical simulation. The proposed method has important application prospects for the non-destructive testing of complex invisible fractures in concrete.