, Volume 32, Issue 1, pp 81-92

Numerical and Experimental Study of Crack Depth Measurement in Concrete Using Diffuse Ultrasound

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Abstract

This paper presents a combined numerical and experimental study on the diffuse ultrasonic measurement technique for determining the depth of surface breaking cracks in concrete. A finite element (FE) model for the dissipative diffusion in a two-dimensional domain with a surface breaking crack is developed using a commercial FE package; for this purpose, the dissipation term is eliminated by a simple change of variables. Three concrete blocks with a crack depth between 25.4 mm to 101.6 mm are prepared. Diffuse ultrasonic measurements are performed on uncracked and cracked concrete blocks, from which the diffuse energy evolution curves are obtained. The basic material parameters of the hardened concrete, i.e. the diffusivity and dissipation, are retrieved, which are needed for the numerical simulations. The crack depths are then determined by comparing the experimental and numerical arrival times of the average diffuse ultrasonic energy. Various geometrical configurations that arise in real-world concrete structures are simulated including an inclined crack, a partially closed crack, two parallel cracks, and a crack with an underlying reinforcement bar. The objective is to investigate the possible limitations of the diffuse ultrasonic measurement technique when implemented in real concrete structures. Finally, it is shown that the time of flight (TOF) of the average diffuse ultrasonic energy constitutes the theoretical basis of the present diffuse ultrasonic measurement of macroscopic cracks and therefore the present diffuse ultrasonic method forms another kind of TOF technique.