Fiber Effects

Evaluation of Fiber Distribution and Alignment in Structural UHPC Elements

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Abstract

The high tensile strength and excellent post-cracking ductility of ultra-high performance concrete (UHPC) makes it attractive for structural applications. This desirable behavior derives in part from a dense network of fibers - often made of high strength steel - that carry tensile loads, even after the concrete has cracked. The orientation and spatial arrangement of the fibers has a significant impact on the ability of the UHPC to carry these stresses. However, because UHPC is typically placed as a highly flowable material, the fibers have a tendency to align along the direction of flow and may also segregate through the depth of the element, thereby altering the local mechanical properties of the UHPC within the structural element. This paper presents a brief review of fiber distribution and alignment in UHPC composites and the associated impact on the performance of structural UHPC elements. An image analysis technique is described to characterize distribution and alignment of fibers on a cut surface,after the exposed fiber surfaces were highlighted by treatment with a copper sulfate solution. A “fiber alignment factor” is introduced to relate the flexural performance of sawed beams to fiber distribution and alignment. Fiber alignment parameters are compared to the theoretical parameters obtained for a random (isotropic) distribution of fibers to characterize the influence of preferential alignment on the mechanical response of the UHPC beams. Extension of the image analysis technique to characterizing fiber distribution and alignment in field-cast structural elements is also discussed.

Keywords: UHPC, flexural testing, image analysis, fiber alignment, fiber distribution

How to Cite:

Wagner, E. (. & Lawler, J. S., (2019) “Evaluation of Fiber Distribution and Alignment in Structural UHPC Elements”, International Interactive Symposium on Ultra-High Performance Concrete 2(1). doi: https://doi.org/10.21838/uhpc.9676