No. 10. - Concrete Structures in the 21st Century - First fib Congress Proceedings Vol. 2 - 13-19 October 2002 - Osaka, Japan - Condensed Papers PDF format

Today's prestressing steels—such as cold-drawn prestressing strand, cold-drawn wire, and hot-rolled prestressing bars—are generally of excellent quality when produced in accordance with well-recognized standards such as ASTM A416, BS 5896, Draft EN 10138, and JIS G3536 and G3109, or equivalent specifications. These materials exhibit outstanding properties in terms of strength, ductility, toughness, fatigue resistance, and resistance to stress corrosion, and they can be safely anchored using well-established and practical anchorage systems.

However, to ensure durable prestressing tendons, these steels must be adequately protected against corrosion. The objective of corrosion protection is to achieve a design life for the tendons that is comparable to that of the structure in which they are installed. In designing corrosion protection systems, it must be recognized that most parts of the tendons are generally inaccessible during their service life and that individual components—or even entire tendons—are typically not replaceable. Even where special provisions are made to allow for replacement, such measures should be regarded as exceptional and limited to emergency situations. Therefore, corrosion protection systems should be designed to perform effectively throughout the entire design life.

Corrosion protection begins at the manufacturing stage and includes temporary protective measures during handling and installation. It is now widely recognized that durability cannot be reliably achieved through a single layer of protection. As a result, the concept of multi-layer protection has been developed.

Within this concept, the first—and perhaps most important—layer of protection is the overall design of the structure. A key objective at this stage is to prevent water ingress and to ensure rapid drainage where exposure occurs. A second layer of protection may be provided through waterproofing membranes, particularly on critical surfaces exposed to water and aggressive agents such as de-icing salts. A third layer is achieved through the use of dense, low-permeability concrete specifically designed to limit the ingress of harmful substances.

The final layers of protection, applied directly to the prestressing steel, serve as the last line of defense and become critical only if the preceding layers are compromised. It is these final protective systems applied directly to the prestressing steel that are the focus of this paper.