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Effect of Fiber Orientation on Dynamic Compressive Properties of an Ultra-High Performance Concrete

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Technical Report

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U.S. Army Engineer Research and Development Center Vicksburg United States

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Casting structural elements with ultra-high performance concrete UHPC tends to create preferential fiber alignment, which affects the strength and must be accounted for in design. To date, most work on fiber-orientation effects has been in tension rather than compression. This work characterizes the fiber orientation occurring in a typical UHPC beam and how that orientation affects compressive behavior at high strain rates. Specimens 36 total were cored from the beam, and their fiber orientations were non-destructively evaluated using x ray computed tomography. Fibers showed flow-induced alignment along the length of the beam. The perpendicular orientation number was used to describe orientation, as fibers perpendicular to the load were most effective in crack bridging. Quasi-static compressive strength appeared to increase with perpendicular orientation number, but the correlation is uncertain due to data limitations. Dynamic tests at strain rates of 130 to 200 s-1 were performed with a split-Hopkinson pressure bar. Dynamic compressive strength was independent of orientation number in these tests, although results suggested that the distribution and orientation of fibers influenced crack formation. The strain at peak stress, a measure of ductility, increased up to 25 percent over the range of perpendicular orientation numbers tested.

Subject Categories:

  • Ceramics, Refractories and Glass
  • Military Forces and Organizations

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