Seminar Series - 1999-2000

Diffusion of Ultrasound in Concrete

Phanidar Anugonda
Department of Engineering Mechanics
University of Nebraska - Lincoln
Lincoln, NE 68588
Advisor:  Joseph A. Turner

Date:  Friday, March 24, 2000
Time:  10:00 a.m.
Place:  W106 Nebraska Hall


Concrete plays an essential role in many aspects of the nation's infrastructure. Concrete structures such as roads, airfields, dams, and buildings are continually subject to effects, which degrade their structural integrity. Assessment of damage is critical if accurate predictions of the remaining life are to be made. As a part of the assessment process, damage characterization using experimental inspection methods is necessitated. Such inspection techniques must be portable, easy to use, robust, and based on rational physical principles.

The propagation and scattering of ultrasound in concrete is used to study damage evolution in concrete. The heterogeneous composition of concrete causes the ultrasound to scatter considerably. In the limit of many scattering events, the ultrasonic energy density in circular cylinders of concrete is shown to evolve in accordance with a one-dimensional diffusion equation. The experiments were carried over the frequency range of 100-500 kHz. Such frequencies are well above typical frequencies used for concrete inspection. Values of the elastic diffusivity, D, and dissipation, s , were recovered from the experiments. The diffusivity, which is a measure of the microstructure, is shown to correlate with concrete damage. The stochastic wave propagation model is in basic agreement with the experimental values for undamaged concrete. This technique also allows the true dissipation from viscoelastic effects in the cement to be assessed directly. It is seen that the water-cement matrix alone affects dissipation. It is anticipated that the use of these higher frequencies will result in new techniques for characterizing material properties and damage in concrete.


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