Q. What is the optimum length and configuration of steel fiber to use for a given application?
There is a single question to be asked before choosing the length and configuration of the steel fiber to use: Are the steel fibers intended to enhance durability and flexural strength properties or provide post first crack benefits (toughness)? If the answer is the former then a 1" continuously deformed fiber will yield the best results. Here we are looking at critical fiber spacing and a good bond between the fibers and mortar. If the latter is the design concern, then a 2" continuous deformed steel fiber is typically specified. Here the steel fiber anchor length across a crack is important to achieving the desired toughness index.

In the ACI design methods for plain structural concrete (I.e., 302, 330, 360) a solid, monolithic concrete element is considered to define the load carrying properties. We know that more fibers decrease the critical fiber spacing thus improving the mechanical cracking properties of the concrete, say a 3/4" long steel fiber. We also know that steel fibers will enhance the flexural strength of the plain structural concrete. A 1" (25mm) long fiber will yield the best results. Since the ACI design methods use the pre-first crack concrete, Nycon will recommend the l" (25mm) long steel fibers for these design applications. Our reason being, the 1" (25mm) long fibers will address mechanical cracking and more importantly the flexural strength gain. The 2" (50mm) long steel fibers are used where post first crack properties of the concrete composite are being considered.

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