The STEELIKE UHPFRC mix design family
Why not glass fibers or smaller pva fibers?
Answer: My research has shown that glass fibers grab air like what happens when you plunge your arm into cold water. I am testing adding mono-filiment glass fibers at this time but the specified pva fibers have shown excellent results. Also, glass fibers too close to or on the surface tend to ghost or show. Lastly glass fibers can not easily be sanded or ground off. When I first started to design this mix years ago, I tried every fiber I could get my hands on. And at a dose that the fibers actually do anything, say 3%, I often ended up with a mix that looked like something my lawnmower spit out when I tried to cut the grass after I let it grow too high. They also entrained too much air, destroyed the flow and increased the cream I then had to remove. It's all about surface area. Given the same weight, the same amount of really small fibers have way too much suface area for a mix design like this. They eat up water. And I refused to tell people they had to vibrate everything to make it work, let alone of the expense to do so.
CUSTOM METAL FIBERS:
When I tried using metal fibers they pull out too easily, what's different about yours?
Traditional metal fibers have the wrong aspect ratios that being the length in relationship to the diameter. More importantly they are too smooth/slippery and are too stiff, (they won't bend which you want some to do), so they pull out faster than the pva fibers. The problem is that unless you acid etch them or somehow etch them they will do very little. The 2 inch hooked ones work great in 6 inch thick road pours but are gigantic in our world. Can you imagine a 1/4" thick tile with paperclips? Even the available metal fibers of the right size, if you don't need to buy a pallet, are going to pull out easily. Google precipitated silica and you'll start to understand the labor involved in etching fibers. I went to several manufacturers until I found one that would custom make me the right fiber. It is the exact length, diameter and material needed and they are pre-etched for me. That alone is not enough for I needed an additive in my mix to decrease pull-out.
Won't the metal fibers rust?
Answer: No, at least not in a visual way or in a way that would cause a structural issue.
Rust needs moisture and oxygen. The density of this mix is that of which has very little water to begin with, just about no air and has little absorption capabilities. So once cured and sealed the encapsulated metal fibers are fossilized for ever.
Steelike's custom metal fibers are available by the pound. They are sold in 1 and 10 pound bags and 50 pound boxes. Larger size packages are available.