Quantitative Damage Assessment of Concrete by Diffuse Ultrasonic Methods

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Damage to concrete structures is caused by overloading, fatigue damage,thermal damage, or a combination of these and other factors. The repair ofdamaged concrete structures costs federal, state, and local governmentsbillions of dollars annually. Quantitative assessment of damage usingnondestructive methods is essential for determining the structuralintegrity of structures and for predicting the remaining usable life. Theproposed research will address these needs through the study of ultrasoundpropagation in concrete at frequencies higher than those typically used forconcrete inspection. The combined experimental and theoretical study willprovide insight into the propagation, scattering, and dissipation ofultrasound. The influence of overloading, fatigue damage, thermal damage,and structural reinforcement on diffuse ultrasound propagation will also beinvestigated. The proposed high frequency ( 100 kHz) approach will improvethe detection of smallscale damage by using wavelengths that are shorterthan those most widely used. The objectives of the proposed research duringthe threeyear period are to:(1) Develop a model describing the propagation, scattering, and dissipationof ultrasound through both undamaged and damaged concrete,(2) Corroborate the developed model experimentally, and(3) Examine the effects of overload damage, mechanical fatigue damage, andthermal cycling damage on diffuse ultrasound propagation.Objectives (1) and (2) will be achieved using analysis techniques alreadydeveloped to describe wave propagation through heterogeneous media. Similardiffuse-field techniques have been particularly successful forcharacterizing polycrystalline microstructures and geophysical media.Concrete inspection research has not yet benefited from these newtechniques. Objectives (2) and (3) will be achieved using both contacttransducer techniques and ultrasonic immersion tank methods which have beendeveloped for the study of diffuse ultrasound propagation.The scientific merit of the proposed research lies in: (i) the statisticalwave propagation approach used, (ii) the highfrequency diffuse ultrasonicmethods employed, and (iii) the combination of theoretical and experimentalresearch which will provide experimental corroboration of the developedtheories. It is anticipated that the research will lead to new techniquesfor assessing damage in concrete structures. The proposed research alsowill have significant impact on the educational training of graduate andundergraduate students in nondestructive evaluation techniques applied toessential infrastructure materials.