Use of network theory to improve the ultrasonic tomography in concrete.

The ultrasonic tomography is an important tool in nondestructive evaluation of concrete structures. It is usual to consider in ultrasonic reconstruction that the mechanical waves only propagate in straight-lines between the transmitter and the receiver transducers, corresponding to the behavior in a homogenous material. In a concrete specimen, however, mechanical waves may deviate from an internal flaw, which affects the resulting tomograms. In this study, the ray tracing technique based on the Network Theory, which allows to consider waves not travelling in a straight-line, was incorporated into the tomography processing. Experimental tests were carried out on concrete specimens with different internal flaws. The results indicated the importance of using the ray tracing technique to properly detect the size and the shape of internal flaws, improving the obtained tomograms. All the necessary algorithms for the application of the Network Theory were presented.