Durability of concrete and cement composites

Mechanisms of corrosion-assisted brittle fracture

The type and manner of corrosion are essential influencing factors affecting the behaviour of prestressing steels under unforeseen or inappropriate service con- ditions. Simply determining that corrosion was involved does not analyse a failure sufficiently, nor will it help in future damage prevention. Depending on the prevailing corrosion situation and the load conditions, as well as the pre- stressing steel properties, the following kinds of fracture can be distinguished:

· Brittle fracture due to exceeding the residual load capacity. Brittle fracture is particularly promoted by:
± local corrosion attack (pitting), and
± hydrogen embrittlement.
· Fracture as a result of stress corrosion cracking, where we distinguish between:
± anodic stress corrosion cracking, and
± hydrogen-induced stress corrosion cracking.
· Fracture as a result of fatigue and corrosion influences, distinguishing between:
± corrosion fatigue cracking, and
± fretting corrosion/fretting fatigue.

In the following sections, these types will be described in more detail with regard to prestressed concrete construction.

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