Effects of different types of fibers and fiber mixes on fresh and hardened properties of ultra-high performance concrete

The effect of different types of fibers and fiber mixes on fresh and hardened properties of commercial ultra-high performance concrete (UHPC) were investigated. Six types of metallic and non-metallic commercially available fibers, including ones commonly used in UHPC and ones not investigated in prior work, were evaluated. Eighteen mixtures with different fiber dosages and combinations are prepared and tested for flowability, compressive strength, flexural properties, and bulk resistivity. Generally, the fibers, with the exception of polyethylene fibers did not affect flowability. All fibers affected mechanical behavior significantly. Depending on fiber type and dosage, compressive strength was - 23 to + 19% of the value of the mixture without fibers. Polyethylene fibers and their blends with steel fibers showed excellent flexural properties. Compared to the control mixture, selected binary mixtures showed improved flexural and compressive strength and synergies. Selected binary mixtures showed improved flexural strength and a lower cost per flexural strength, but a somewhat reduced compressive strength. Clearly, there are complex cost, compressive strength, flexural strength, and flow tradeoffs that can be leveraged based on the required application.