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From my understanding plastic mesh would be pointless. Concretes compressive strength is extremely high but the negative of conrete is its tensile strength tends to be much lower. A good rule of thumb is tensile str is 1/4 the compressive str. The problem with plastic mesh is it may have a higher ultimate (breaking point) tensile strength than concrete but it will stretch quite a bit under stresses allowing the concrete to break before any support kicks in. you want to use a material with high tensile strength and low elongation for reinforcement. Also you where measure the concrete on its impact ability not load strength. What is your intended use for this?