Ultrasonic and X-ray Tomographic Imaging of Highly Contrasting Inclusions in Concrete Specimens

There are several techniques that may be used in the tomographic imaging of structural and geotechnical systems. X-ray tomography and ultrasonic imaging are two of the extreme techniques as functions of resolution and costs. On one hand, X-ray tomography allows the collection of high-resolution images in small specimens that may be removed from the structure. The application of X-rays in the field is not recommended due to cost and safety issues. On the other hand, ultrasonic testing may be used in the field to obtain stiffness images with lower resolution due to problems of high attenuation, diffraction and scattering around aggregates and inclusions. However the cost of ultrasonic testing is much lower than X-ray imaging systems. This paper presents experimental results of X-ray and ultrasonic tomographic imaging of concrete cylindrical specimens prepared with low-density and velocity and high-density and velocity inclusions. These specimens present the extremes of contrast for the two techniques. Quantitative and qualitative analysis of the results show that the results from each technique are complementary: X-ray tomography may be efficiently used for the collection of advanced model parameters while ultrasonic imaging may be used for the QC/QA of structural and geotechnical elements in the field.