An X-Ray Tomography Investigation of Bond in Reinforced Concrete

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AbstractA number of reinforced concrete bond experiments will be conducted inside a high-energy x-ray ct scanner. The goal is to obtain a set of three-dimensional high-resolution volumetric images of bond-zone damage patterns for near full-scale specimens under loading. These images will permit, to an unprecedented degree, the observation and quantification of the initiation and progression of critical internal deformation and damage in the bond-zone. They will also allow the validation of high-fidelity numerical models that will ultimately support the reliable upscaling from rib-level models to bar-level models.Bond behavior in reinforced concrete is a problem of enormous practical importance because it often controls the behavior of members and, by implication, behavior of the whole structure. Yet, the details of bond-zone damage initiation and evolution are, in the current state of the art, poorly understood. The result is that the local data required for understanding the details of the bond mechanism, and necessary for developing reliable numerical models, have not been available to date. x-ray tomography, because of its dense, non-invasive, and non-destructive nature, has the potential to fulfill the need for local data and to revolutionize the state of knowledge of bond behavior.The novelty and difficulty of the proposed tests come from the fact that: (1) they are large scale, and hence high-energy (linear-accelerator) x-ray sources are necessary to penetrate the specimens and obtain high-resolution 3d-ct reconstructions; and (2) the imaging has to be performed under significant loading, and hence a complete testing frame (with actuators, fixtures, etc.) has to be placed inside the scanner. In addition to providing answers to questions about bond that have plagued engineers for decades, the project will have a far-reaching impact on education. The 3d-ct archive of data sets together with high-quality volumetric renderings of the tests will be packaged in web-available modules and distributed nationally. They will enable a new generation of students to see how the interior of the RC systems that they study actually appear and how their internal microstructure evolves due cracking, and crushing under loading. The media-rich catalog of data produced will also provide the opportunity to demonstrate to k-12 students the application of modern technology to solving civil material design problems.