Hydrogen-assisted stress-corrosion of prestressing wires in a motorway viaduct

This paper deals with the stress corrosion cracking of cold-drawn stress relieved prestressing wire in a prestressed reinforced-concrete structure due to the influence of atmospheric water and especially the chlorides which were present during the winter salting of the road pavements of a motorway viaduct in Slovenia. Twenty-two years after the bridge was first opened for traffic, numerous wires in the prestressing cables had become brittle, and had broken and many others were damaged, to a greater or lesser degree, by corrosion and the effect of stress corrosion supported by the additional operation of hydrogen at the crack tips. Investigations showed that as the degree of corrosion increased the mechanical properties of the steel, particularly its toughness, were reduced drastically. As a result, such material is unable to prevent the initiation or spreading of cracks in the case of the static and dynamic loadings occurrring on the bridge. Systematic SEM investigations of the morphology of the fracture surfaces of the wires confirmed the author's assumption that stress corrosion and hydrogen embrittlement had made possible the occurrence of brittle areas with cleavage fracture surfaces, the proportion of which increased with an increase in the degree of corrosion.