There are three common post-tensioning systems used in construction: bonded, unbonded, and external. In bonded systems, the steel tendons are tensioned and then bonded to the concrete (usually by grouting inside the surrounding duct), creating a solid composite action with the slab. Unbonded systems use tendons encased in a grease-filled plastic sheath that are not grouted to the concrete, allowing them to move freely within the slab – these are common in building floors. Finally, external post-tensioning places the tendons outside the concrete member (often used in bridge retrofits or special structures) . Each type is chosen based on the structure’s design needs and maintenance considerations.

Bonded, Unbonded, External: Which PT System Fits Your Project?

• Bonded (grouted) – strands are grouted into ducts, locking them to the concrete.
• Unbonded (grease-filled sheaths) – tendons remain free to move; anchored only at the ends.
• External / monostrand / multistrand variants – tendons placed outside or grouped for large loads.