In principle, you need a structural material (aggregate) and a binder (asphalt or cement). Rock is a plentiful strong material for aggregate, but broken up concrete, glass or plastics works as well.
I’m not seeing what the point of the low melting point metal would be unless your description is to use metal and plastic as some combination of aggregate and binder. If that is the case, then current materials will be far more economical.
MKDesign 