I am looking to pretension reinforced concrete composite structure. The trouble I am having is two fold. One to set the bond charactoristics between the bar and the concrete, ie bond strength. The second is the ability to prestress the rebar. In real lift I stretch the bar, (either by heating or hydrualic jacks) pour the concrete, then release the bar once the concete is set. This forces the concrete in a perminent compressive state. This pre stress is available as a bolt but this does not distrubute the load correctly though out the structure.