Ground penetrating radar (GPR) has become a viable technology for non-destructive condition assessment of reinforced concrete structures. Interpretation of the radar signal is typically performed through preliminary filtering techniques and interpretation is based on viewing numerous signals in the form of a scan. Although anomalies can be evident in the scanned image, quantification and interpretation of the main issue remain ambiguous. This article presents the ambiguity and common methods of interpretation based on response amplitude and travel time. An integrated medium is developed and used as a forward modeling tool to generate a realistic radar reflection of a reinforced concrete bridge deck with defects. A healthy deck reflection is obtained from a separate model and is combined with an inverse solution to quantifiably estimate unknown subsurface properties such as layer thickness and dielectric constants of subsurface materials evident in the realistic radar trace as well as. The forward modeling tool and associated model based assessment provides an objective computational alternative to the interpretation of scanned images.
Several types of pavement surface distress can be attributed to delamination between hot-mix asphalt (HMA) layers. Longitudinal cracking in the wheel path and tearing in the surface are two common types of visual distress that are caused by delamination between layers. HMA delamination is primarily due to layer debonding or stripping. Debonding occurs when there is improper tack between paved HMA layers or between an HMA overlay and concrete pavement. Stripping develops when the aggregates and asphalt binder are incompatible, adhesion is lost, and water separates the asphalt binder from the aggregate. These conditions that cause pavement distress cannot be detected by visual inspection of the pavement, particularly in the early stages of the problem. The distress-cracking or tearing-are the first indicators that delamination may be occurring within the pavement layers. Agencies that maintain a roadway network need a test method to detect the location and severity of delamination before the pavement deficiency causes visual pavement distress. The test method should be applicable to network-level pavement condition assessment, projectlevel design investigation to select the correct rehabilitation strategy, and construction quality assurance. Coring is often used to measure the depth, type, and severity of delamination after the visual distress appears. This test method is destructive and is not suitable for effective evaluation of long lengths of pavement. Nondestructive testing (NDT) methods are needed to identify the presence, location (depth and area), and severity of delamination in a rapid, effective manner. The objectives of this second Strategic Highway Research Program (SHRP 2) study were to determine which NDT technologies could detect delamination and further to develop the most promising methods to accomplish construction, project design, and network-level evaluations. NDT technology for construction quality assurance should have the ability to detect debonding after placement of an HMA lift. NDT technology for project-level investigation should have the ability to provide a detailed identification of the location and severity of delamination. NDT technology for networklevel assessment should have the ability to detect the presence of delamination with the test equipment operating full-lane width at safe vehicle speed. Disciplines Civil and Environmental Engineering T R A N S P O R T A T I O N R E S E A R C H B O RepoRt S2-R06D-RR-1 The Second S T R A T E G I C H I G H W A Y R E S E A R C H P R O G R Copyright InformationAuthors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein.The second Strategic Highway Research Program grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, or FH...
Computational modeling is beneficial in the preparation for nondestructive wave-based sensing. Forward models, which can be implemented through a variety of computational modeling techniques, enable parametric evaluations to assess the functionality of a sensor under different conditions, and are integral to the solution of the inverse problem. The focus of this article is on the comparison of two-dimensional (2D) and three-dimensional (3D) Finite Difference Time Domain (FDTD) models. This article gives a presentation of the accuracy of 2D modeling by comparing FDTD simulations of reinforced bridge deck deterioration in 2D and 3D. Simulations for a healthy and delaminated bridge deck are examined. It is shown that the difference in propaga-tion between the 3D and 2D point sources must be considered and is more pronounced at greater distances from the source location. The effect of scattering from the delamination is visible and, while there is variation in amplitude between the 3D and 2D models, the shapes of the resulting waveforms (including the peak arrival times) are well matched.
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