Impact-Echo Modeling and Imaging Techniques

Deteriorating infrastructure across the United States is an issue that is commonly referred to in todays society, yet there still remains a question about the level of severity. One of the most relied upon infrastructure components are the thousands of bridges that are essential to everyday life. A common structural component among all bridges is the reinforced concrete bridge deck. Internal air pockets and voids can develop over time with no knowledge of their existence. Among the available condition assessments for bridge decks is a technique noted as impact-echo (IE), a common non-destructive evaluation (NDE) system. This method utilizes mechanical waves to develop information about the subsurface conditions.;In this thesis, a synthesis of literature for the impact-echo method will be developed to help understand the progression of the technology and where it stands today. In addition, a model of mechanical wave propagation has been created with both finite element method (FEM) and finite difference time domain (FDTD) method. Advantages and disadvantages of each method will be demonstrated and results from both models will be compared to each other. The impact-echo system was used to gather experimental data on the Northeastern University RoadBED test specimen that contains known void and reinforcement locations. An analytical model of the RoadBED is carried out with the finite element method and results are compared to experimental data. Imaging methods are implemented with both analytical and experimental data to help verify the ability to assess the subsurface condition of a concrete deck. We will verify that the impact-echo method can accurately identify anomalies in the local area of interest. A better understanding of the challenges with analytical modeling will demonstrate future implications for developing a numerical inversion approach for the impact-echo method.