higher tensile strains in the tendons than if they were unbonded, allowing their full yield strength to be realised, and producing a higher ultimate load capacity. Improved crack-controlIn the presence of concrete cracking, bonded tendons respond similarly to conventional reinforcement (rebar). With the tendons fixed to the concrete at each side of the crack, greater resistance to crack expansion is offered than with unbonded tendons, allowing many design codes to specify reduced reinforcement requirements for bonded post-tensioning. Improved fire performanceThe absence of strain redistribution in bonded tendons may limit the impact that any localised overheating has on the overall structure. As a result, bonded structures may display a higher capacity to resist fire conditions than unbonded ones. The benefits that unbonded post-tensioning can offer over bonded systems are: Ability to be prefabricatedUnbonded tendons can be readily prefabricated off-site complete with end-anchorages, facilitating faster installation during construction. Additional lead time may need to be allowed for this fabrication process. Improved site productivityThe elimination of the post-stressing grouting process required in bonded structures improves the site-labour productivity of unbonded post-tensioning. Improved installation flexibilityUnbonded single-strand tendons have greater handling flexibility than bonded ducting during installation, allowing them a greater ability to be deviated around service penetrations or obstructions. Reduced concrete coverUnbonded tendons may allow some reduction in concrete element thickness, as their smaller size and increased corrosion protection may allow them to be placed closer to the concrete surface. Simpler replacement and/or adjustmentBeing permanently isolated from the concrete, unbonded tendons are able to be readily de-stressed, re-stressed and/or replaced should they become damaged or need their force levels to be modified in-service. Superior overload performanceAlthough having a lower ultimate strength than bonded tendons, unbonded tendons' ability to redistribute strains over their full length can give them superior pre-collapse ductility. In extremes, unbonded tendons can resort to a catenary-type action instead of pure flexure, allowing significantly greater deformation before structural failure. Tendon durability and corrosion protection Long-term durability is an essential requirement for prestressed concrete given its widespread use. Research on the durability performance of in-service prestressed structures has been undertaken since the 1960s, and anti-corrosion technologies for tendon protection have been continually improved since the earliest systems were developed. The durability of prestressed concrete is principally determined by the level of corrosion protection provided to any high-strength steel elements within the prestressing tendons. Also critical is the protection afforded to the end-anchorage assemblies