of unbonded tendons or cable-stay systems, as the anchorages of both of these are required to retain the prestressing forces. Failure of any of these components can result in the release of prestressing forces, or the physical rupture of stressing tendons. Modern prestressing systems deliver long-term durability by addressing the following areas: Tendon grouting (bonded tendons)Bonded tendons consist of bundled strands placed inside ducts located within the surrounding concrete. To ensure full protection to the bundled strands, the ducts must be pressure-filled with a corrosion-inhibiting grout, without leaving any voids, following strand-tensioning. Tendon coating (unbonded tendons)Unbonded tendons comprise individual strands coated in an anti-corrosion grease or wax, and fitted with a durable plastic-based full-length sleeve or sheath. The sleeving is required to be undamaged over the tendon length, and it must extend fully into the anchorage fittings at each end of the tendon. Double-layer encapsulationPrestressing tendons requiring permanent monitoring and/or force adjustment, such as stay-cables and re-stressable dam anchors, will typically employ double-layer corrosion protection. Such tendons are composed of individual strands, grease-coated and sleeved, collected into a strand-bundle and placed inside encapsulating polyethylene outer ducting. The remaining void space within the duct is pressure-grouted, providing a multi-layer polythene-grout-plastic-grease protection barrier system for each strand. Anchorage protectionIn all post-tensioned installations, protection of the end-anchorages against corrosion is essential, and critically so for unbonded systems. Several durability-related events are listed below: Ynys-y-Gwas bridge, West Glamorgan, Wales, 1985A single-span, precast-segmental structure constructed in 1953 with longitudinal and transverse post-tensioning. Corrosion attacked the under-protected tendons where they crossed the in-situ joints between the segments, leading to sudden collapse. Scheldt River bridge, Melle, Belgium, 1991A three-span prestressed cantilever structure constructed in the 1950s. Inadequate concrete cover in the side abutments resulted in tie-down cable corrosion, leading to a progressive failure of the main bridge span and the death of one person. UK Highways Agency, 1992Following discovery of tendon corrosion in several bridges in England, the Highways Agency issued a moratorium on the construction of new internally grouted post-tensioned bridges and embarked on a 5-year programme of inspections on its existing post-tensioned bridge stock. The moratorium was lifted in 1996. Pedestrian bridge, Charlotte Motor Speedway, North Carolina, US, 2000A multi-span steel and concrete structure constructed in 1995. An unauthorised chemical was added to the tendon grout to speed construction, leading to corrosion of the prestressing strands and the sudden collapse of one span, injuring many