Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Eine Plattform für die Wissenschaft: Bauingenieurwesen, Architektur und Urbanistik
Long-term effects of cathodic protection on prestressed concrete structures: Hydrogen embrittlement of prestressing steel
The issue of safe cathodic protection (CP) limits for prestressing steel in concrete was addressed in regard to concerns over hydrogen embrittlement (HE). The local environment at steel-concrete interface was found to vary as a function of vertical position within a laboratory-scale marine bridge piling. Embedded pH electrodes indicated the pH within a steel crevice embedded within a concrete piling decreased from 11.5 to 6.5 in the atmospheric zone 30.5 cm (12 in.) above the water line. Hydrogen permeation was detected using embedded sensors at applied potentials (Eapp) more positive than the reversible potential for hydrogen production calculated for alkaline pore solutions (pH > 12.6). A safe limit based on the reversible electrode potential (REP) would require knowledge of pH and Eapp as a function of vertical position, as well as an understanding of their influence on HE. Constant extension rate tensile testing (CERT) was performed on notched prestressing steel tensile specimens at various cathodic polarization levels in: (1) saturated Ca(OH)2, ( 2) ASTM artifical ocean water, (3) under a mortar cover in artificial ocean water, an (4) in pH 4 and pH 6 Ca(2+)-containing environments simulating ferrous ion hydrolysis on corroding prestressing steel. CERT results were combined with permeation measurements to determine the relationship between steel mobile hydrogen concentration (CH) and fracture initiation stress (sigma i) in each environment over a series of cathodic potentials. A relationship of the form sigma1 = sigma0) -alphalog(CH/C0), where sigma0 is the fracture initiation stress in the absence of mobile hydrogen and C0 is the mobile hydrogen concentration at or below which no hydrogen embrittlement is observed, was found independent of environment and pH. The previously reported fixed cracking threshold of -900 mVSCE in Ca(OH)2 solutions pH adjusted with hydrochloric acid (HCl), irrespective of pH (from 7 to 12.5), was explained. Decreasing pH in these environments produced a roughly constant CH at Eapp = -900 m-vSCE due to the opposing influences on hydrogen uptake of increasing hydrogen overpotential but decreasing availability of a Ca(OH)2 recombination poison.
Long-term effects of cathodic protection on prestressed concrete structures: Hydrogen embrittlement of prestressing steel
The issue of safe cathodic protection (CP) limits for prestressing steel in concrete was addressed in regard to concerns over hydrogen embrittlement (HE). The local environment at steel-concrete interface was found to vary as a function of vertical position within a laboratory-scale marine bridge piling. Embedded pH electrodes indicated the pH within a steel crevice embedded within a concrete piling decreased from 11.5 to 6.5 in the atmospheric zone 30.5 cm (12 in.) above the water line. Hydrogen permeation was detected using embedded sensors at applied potentials (Eapp) more positive than the reversible potential for hydrogen production calculated for alkaline pore solutions (pH > 12.6). A safe limit based on the reversible electrode potential (REP) would require knowledge of pH and Eapp as a function of vertical position, as well as an understanding of their influence on HE. Constant extension rate tensile testing (CERT) was performed on notched prestressing steel tensile specimens at various cathodic polarization levels in: (1) saturated Ca(OH)2, ( 2) ASTM artifical ocean water, (3) under a mortar cover in artificial ocean water, an (4) in pH 4 and pH 6 Ca(2+)-containing environments simulating ferrous ion hydrolysis on corroding prestressing steel. CERT results were combined with permeation measurements to determine the relationship between steel mobile hydrogen concentration (CH) and fracture initiation stress (sigma i) in each environment over a series of cathodic potentials. A relationship of the form sigma1 = sigma0) -alphalog(CH/C0), where sigma0 is the fracture initiation stress in the absence of mobile hydrogen and C0 is the mobile hydrogen concentration at or below which no hydrogen embrittlement is observed, was found independent of environment and pH. The previously reported fixed cracking threshold of -900 mVSCE in Ca(OH)2 solutions pH adjusted with hydrochloric acid (HCl), irrespective of pH (from 7 to 12.5), was explained. Decreasing pH in these environments produced a roughly constant CH at Eapp = -900 m-vSCE due to the opposing influences on hydrogen uptake of increasing hydrogen overpotential but decreasing availability of a Ca(OH)2 recombination poison.
Long-term effects of cathodic protection on prestressed concrete structures: Hydrogen embrittlement of prestressing steel
Langzeit-Einfluß des kathodischen Korrosionsschutzes auf Spannbeton-Elemente: Wasserstoffversprödung von vorgespanntem Stahl
Enos, D.G. (Autor:in) / Williams, A.J. jun. (Autor:in) / Scully, J.R. (Autor:in)
Corrosion, Houston ; 53 ; 891-908
1997
18 Seiten, 20 Bilder, 2 Tabellen, 35 Quellen
Aufsatz (Zeitschrift)
Englisch
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Hydrogen Embrittlement of Tendon in Prestressed-Concrete Structures under Cathodic Protection
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Hydrogen Embrittlement of Prestressing Steel
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Cathodic protection for prestressed concrete structures
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