Quantitative Damage Assessment of Concrete by Diffuse Ultrasonic Methods

混凝土结构的损伤是由超载、疲劳损伤、热损伤或这些因素和其他因素的组合引起的。修复损坏的混凝土结构每年要花费联邦、州和地方政府数十亿美元。使用无损方法对损伤进行定量评估对于确定结构的完整性和预测剩余使用寿命至关重要。拟议的研究将通过研究超声在混凝土中的传播频率，而不是通常用于混凝土检查的频率，来解决这些需求。实验与理论相结合的研究将对超声波的传播、散射和耗散提供深入的了解。超载、疲劳损伤、热损伤和结构加固对弥散超声传播的影响也将被研究。提出的高频（100千赫）方法将通过使用比最广泛使用的波长更短的波长来改进对小规模损伤的检测。为期三年的研究目标是：(1)建立一个模型，描述超声波在未损伤和受损混凝土中的传播、散射和耗散；(2)通过实验证实所开发的模型；(3)检查过载损伤、机械疲劳损伤和热循环损伤对弥散超声传播的影响。目标(1)和(2)将使用已经开发的分析技术来描述波在异质介质中的传播。类似的扩散场技术在表征多晶微结构和地球物理介质方面特别成功。混凝土检测研究尚未受益于这些新技术。目标(2)和(3)将通过使用接触式换能器技术和超声浸没槽方法来实现，这两种方法是为研究弥漫性超声传播而开发的。提出的研究的科学价值在于：(i)使用统计波传播方法，（ii）使用高频弥散超声方法，以及（iii）理论和实验研究的结合，这将为发展的理论提供实验证实。预计该研究将导致混凝土结构损伤评估的新技术。本研究也将对研究生和本科生在基础设施材料无损评估技术方面的教育训练产生重大影响。

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.