Recycled Fibers in Flexible Concrete

Another thought I had about flexible concrete, "What if the fibers within the concrete were recycled and used in another slab of concrete?" A study conducted by Shi Yin and others from James Cook University in Australia (found here) tested exactly that. They found some interesting stuff from this study. With multiple samples of concrete tested at both high (5800 psi) and low (3600 psi) stress levels, they found that the recycled fibers weren't as feasible as the new fibers in the higher stress test. This is due to the fact that, due to being placed under stress previously, their tensile strength was greatly reduced which meant that they have a higher chance of breaking under the higher stress. But, when tested in the lower stress test, the recycled fibers outperformed the new fibers. This may seem weird but it's due to a mechanical property called the Young's Modulus, a relation between stress and elongation of the fiber. When previously placed under stress, these fibers tend to increase their Young's Modulus causing the fiber to better resist elongation when under stress. Due to this, the recycled fibers would barely elongate under a lower stress when compared to the new fibers, which had a lower Young's Modulus. This is a very interesting find that kind of didn't go the way I thought it would (or would have liked to see it go). While it would be useful to reuse these fibers in sidewalks after being used in roadways, it will, unfortunately, not be useful in another roadway which will not help in reducing the price of flexible concrete.