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、温度损伤或这些因素和其他因素的组合造成的。修复受损的混凝土结构每年要花费联邦、州和地方政府数十亿美元。使用非破坏性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是必不可少的。拟议的研究将通过研究超声波在混凝土中的传播频率高于通常用于混凝土检测的频率来满足这些需求。实验和理论相结合的研究将使我们对声波的传播、散射和消散有深入的了解。此外，还将研究超载、疲劳损伤、热损伤和结构加固对扩散超声传播的影响。建议的高频(100 KHz)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范围损伤的检测。这项为期三年的研究的目标是：(1)建立一个描述超声在未损伤和受损混凝土中的传播、散射和耗散的模型，(2)通过实验证实所开发的模型，以及(3)检验超载损伤、机械疲劳损伤和热循环损伤对扩散超声传播的影响。目标(1)和(2)将使用已开发的描述波在非均匀介质中传播的分析技术来实现。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)将使用为研究扩散超声传播而开发的接触式换能器技术和超声浸没槽法来实现。拟议研究的科学价值在于：(I)采用统计波传播方法，(Ii)采用高频扩散超声方法，以及(Iii)理论和实验研究相结合，这将为所发展的理论提供实验证实。预计这项研究将带来评估混凝土结构损伤的新技术。这项研究还将对研究生和本科生在应用于基本基础设施材料的无损评估技术方面的教育培训产生重大影响。

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.