Corrosione delle armature da precompressione

Corrosion can have serious consequences when it occurs in pre-stressed or posttensioned concrete structures. Due to high loads applied to the tendons or bars and low fracture toughness that characterize the high strength steels, the consequences of corrosion attacks are more dangerous than in the case of conventional reinforced structures. As a matter of fact, even tiny localized attacks can determine the failure under service of tendons or bars. In the case of pre-tensioned structures, corrosion can be brought about by the penetration of carbonation or chlorides through the concrete cover, while in post-tensioned structures corrosion usually arises as a consequence of ineffective filling of ducts with cement grouts or other protective materials. Under specific conditions, localized attacks can degenerate into cracks promoted by hydrogen embrittlement. In this paper the main causes of corrosion are illustrated, showing that the protection of high strength steel requires even more care than the protection of conventional reinforcing bars.