PSI - Issue 62

Edoardo Proverbio et al. / Procedia Structural Integrity 62 (2024) 285–298 Author name / Structural Integrity Procedia 00 (2019) 000–000

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tensile mechanical stresses (Ulf Nürnberger, 2002) provided that there is a particular tendency for steels to passivate in environments containing nitrates in aqueous solution. In prestressed reinforced concrete construction, these conditions can be found in structures used for storing fertilizers and in the ceilings of stables where saltpeter Ca(NO 3 ) 2 can form due to the presence of urea. In the presence of humidity, nitrates can diffuse into the concrete and can cause stress corrosion cracking. Low-carbon concrete steels (with a carbon content between 0.1 and 0.3%) are very susceptible to nitrate-induced stress corrosion cracking. Prestressing steels currently in use, however, are highly resistant to this type of nitrate-induced stress corrosion cracking. Anodic stress corrosion cracking have been also observed in carbonate/bicarbonate environments characterizing, for example, carbonated mortars or concretes (Sanchez et al., 2007). In this context, according to the anodic dissolution mechanism, stress corrosion cracking can occur in a narrow potential range, located in the transition from active to passive behavior, because of the competition between passive film growth and metal dissolution induced by the mechanical failure of the passive layer. In this case it was observed that the initiation of cracks is linked to the anodic dissolution mechanism, while the propagation of cracks can be supported by hydrogen embrittlement mechanisms in the region of the anodic potentials (approximately –300 to +100 mV vs SCE) as shown in Fig. 4 (Proverbio & Longo, 2003).

Fig. 4. SCC on cold drawn prestressing steel wire during anodic polarization in 0.05 M NaHCO3 at pH 8.3 (Proverbio & Longo, 2003)

3. Zinc, galvanized steel and hydrogen embrittlement

As already mentioned, damage from hydrogen is only possible in acidic environments; in the presence of promoters such as sulphides, thiocyanate or arsenic or selenium compounds; in corrosion conditions such as pitting or crevice; if the steel surface is polarized at low potentials (for example if the prestressing steel is in cathodic protection conditions or in contact with zinc or galvanized steel) (U. Nürnberger, 2002).