This is a multi-strand system where one or more tendons are inserted into a metal or plastic duct that is embedded in the concrete. By filling the duct with cementitious grout, the tendons are 'bonded' with the surrounding concrete. This system is more suitable for bridges, tanks and silos, as well as heavily loaded beams in buildings.
This is a mono-strand system wherein the prestressing steel is coated with special grease and so, not actually bonded to the concrete that surrounds it, except at the anchorages. This system is more suitable in slabs and slabs-on-ground for buildings and parking structures, as well as structures where inspection and replacement of the tendons is required.