The effect of Cr VI present in the cement on the active corrosion of galvanized steel was studied. The investigation was performed by means of corrosion potential measurements performed both in concrete and in Ca(OH)2 saturated solution. The obtained results indicate that Cr VI promotes the passivation of galvanized steel due to its inhibitory effect on the zinc corrosion. The higher the concentration of Cr VI, the shorter the time required for the passivation of zinc. When the concentration of Cr VI reaches 15 ppm (referred to the weight of the cement), the passivation occurs immediately after immersion. This acceleration avoids the hydrogen evolution, which causes the rebars adhesion loss during the early age period in contact with concrete, when the cement paste is not yet hardened. A reactivation process, followed by a new passivation, was observed for concentrations of Cr VI ≥ 6 ppm; this behavior does not occur in Ca(OH)2 saturated solution. The reactivation process is attributed to the depletion of Cr VI on the galvanized steel surface, caused probably by the aging of concrete, which consumes the pore solution. The second passivation is stable and is due to the formation of calcium hydroxyzincate.

Effect of Cr VI on the passivation of galvanized steel in concrete / Bellezze, Tiziano; Roventi, Gabriella; Fratesi, Romeo; Timofeeva, Daria. - ELETTRONICO. - (2016). (Intervento presentato al convegno EUROCORR 2016 tenutosi a Montpellier (France) nel 11 - 15 September 2016).

Effect of Cr VI on the passivation of galvanized steel in concrete

BELLEZZE, Tiziano;ROVENTI, Gabriella;FRATESI, Romeo;TIMOFEEVA, DARIA
2016-01-01

Abstract

The effect of Cr VI present in the cement on the active corrosion of galvanized steel was studied. The investigation was performed by means of corrosion potential measurements performed both in concrete and in Ca(OH)2 saturated solution. The obtained results indicate that Cr VI promotes the passivation of galvanized steel due to its inhibitory effect on the zinc corrosion. The higher the concentration of Cr VI, the shorter the time required for the passivation of zinc. When the concentration of Cr VI reaches 15 ppm (referred to the weight of the cement), the passivation occurs immediately after immersion. This acceleration avoids the hydrogen evolution, which causes the rebars adhesion loss during the early age period in contact with concrete, when the cement paste is not yet hardened. A reactivation process, followed by a new passivation, was observed for concentrations of Cr VI ≥ 6 ppm; this behavior does not occur in Ca(OH)2 saturated solution. The reactivation process is attributed to the depletion of Cr VI on the galvanized steel surface, caused probably by the aging of concrete, which consumes the pore solution. The second passivation is stable and is due to the formation of calcium hydroxyzincate.
2016
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/249367
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