I was pouring some concrete and wanted to experiment by adding some plastic to re-enforce the concrete similar to adding fibers. I used regular quickrete and poured it into a plastic container. To one container I added a piece of strap that I had laying around and also a piece of plastic mesh used for gardening that I also had laying around. I tried to place the plastic close to the center of the concrete.
Step 1: Results
After the concrete had hardened for over a week I tested it by dropping each brick onto a my garage floor from waist height. I did this three to four times. The regular concrete was not damaged but the concrete wiith the plastic was broken more with each drop. It looked like the concrete was not bonding well with the plastic and it actually made it much weaker.