For those interested in reinforcing fibers for concrete (these are the chopped strands that help prevent shrinkage cracks and on small scale work help increase tensile strength), there's a new fiber making process from Nycon. They are using post consumer carpets (that translates as old carpets that are about to be thrown away) remade into polypropylene or nylon fibers for added strength in your concrete mix. Old carpets are a huge landfill problem, so this is a great solution.
The new fibers are called Nycon-G. From a recent news release:
"Available in both nylon and polypropylene blends, Nycon-G fibers represent a break-through in green building technology. They are the only fibers on the market today that have no net negative impact on the environment."
I've recommended using fibers as a concrete additive both on the Art Concrete website and my own book, Concrete Handbook for Artists. I particularly like PVA (poly vinyl alcohol) fibers, although these are not part of this green initiative.