I was just going to say that, well not quite but close. Pre-stressed concrete are pre-cast pieces, ie: bridge girders. Strands of cable are ran from one end of the form to another then stressed to a tension strength. Rebar and foam blocks can also be included, for strength and weight issue (foam).Originally Posted by 4x4mike
You could encounter rebar or mesh, as that is used not only to help with shape but with strength as well. I don't see that being much of a problem for what you will be doing.