First, plastics are on a spectrum of bio-degradableness and I have no idea what plastics are used to strengthen concrete. Second, to recycling concrete you cru

First, plastics are on a spectrum of bio-degradableness and I have no idea what plastics are used to strengthen concrete. Second, to recycling concrete you crush it. Crush it to powder and you can use it as aggregate in another batch of concrete. Leave it as big chunks and you can use it as fill. In this kind of recycling, the plastic can go with it just like any other. Personally I prefer to build with wood.