Corrosion Resistance of Cr-bearing Rebar to Macrocell Corrosion Caused by Concrete Cover Crack

2009

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Chloride-laden and carbonated environments were selected for the investigation of corrosion acceleration due to galvanic corrosion of normal rebars in contact with corrosion-resistant Cr-bearing rebars embedded in concrete. Concrete specimens simulating these environments were fabricated using normal steel (SD345) rebars in contact with Cr-bearing rebars and subjected to corrosion-accelerating curing with high temperature/high humidity and low temperature/low humidity cycles. The half-cell potential, corrosion area, and corrosion loss of the normal steel rebars were measured at the specified test ages.No corrosion acceleration due to galvanic corrosion was observed on SD345 rebars in contact with Crbearing rebars in chloride-laden and carbonated concretes, suggesting the possibility of the selective use of Cr-bearing rebars for newly built structures only where necessary and their use as a repair material for patching.

Section: Test Results Of Carbonation Specimens (1) Corrosion Patternsmentioning

confidence: 99%

Probability of Galvanic Corrosion of Cr-bearing Rebars in Concrete

2009

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“…[9][10][11][12] With this as a background, the authors have been investigating the corrosion resistance of Cr-bearing rebars having lower alloying elements, such as chromium, nickel, and molybdenum, than general stainless steel to allow production by processes similar to those of normal steel. [13][14][15] In this study, the service life of concrete structures reinforced with Cr-bearing rebars was investigated in macrocell corrosion environments induced by cover concrete cracking as part of a study for the development of Cr-bearing rebars having corrosion resistance suitable for the corrosive environments to which reinforced concrete structures are to be constructed. Based on the estimated service life, the Cr content of Cr-bearing rebars to achieve a corrosion resistance for up to 100 years was also calculated.…”

Section: Introductionmentioning

confidence: 99%

Service Life Estimation of Concrete Structures Reinforced with Cr-bearing Rebars under Macrocell Corrosion Conditions Induced by Cracking in Cover Concrete

Kyung

Ujiro³

2007

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Cracked concrete members reinforced with Cr-bearing rebars were assumed for the purpose of developing Cr-bearing rebars having the required corrosion resistance in macrocell corrosion environments induced by cracking in cover concrete. The service life of concrete structures reinforced with Cr-bearing rebars was then estimated based on a macrocell corrosion rate model, and their Cr content to achieve a service life of 100 years was calculated. As a result, the service life of concrete reinforced with Cr-bearing rebars was found to increase as their Cr content increased regardless of the corrosive environment type. The calculation also revealed that Cr contents of 16 % or more and 13 % or more would lead to a service life of over 100 years in harsh and moderate chloride attack zones, respectively. In a carbonation zone, the Cr content to achieve a service life of over 100 years was calculated to be 9 % or more.KEY WORDS: Cr-bearing rebar; service life estimation; macrocell corrosion; crack.ISIJ International, Vol. 47 (2007), No. 6, Study OverviewA concrete member reinforced with a Cr-bearing rebar having a single crack was assumed. The penetration rates of Cl Ϫ and CO 2 through the cracked and sound areas were determined to express the material nonuniformity between the cracked and sound areas in terms of the difference in the chloride concentration and carbonation/uncarbonation. Also, the rates of macrocell and microcell corrosion were calculated based on the equations for calculating the polarization resistance and half-cell potential of Cr-bearing rebars, as well as an equation for calculating the concrete resistance, using the corrosion factors as parameters. The amounts of macrocell and microcell corrosion calculated from these corrosion rates were added, and the time required for the sum to reach the threshold amount of rust causing a crack in cover concrete was calculated as the service life. The use of the sum of macrocell and microcell corrosion amounts is intended to incorporate the possibility of their coexistence in rebar under cracked cover concrete. The amount of rust that would cause cracking in cover concrete was adopted as the limit state of reinforced concrete structures. The macrocell corrosion rate was determined using a model consisting of electrical circuits in concrete. Also, the polarization resistance of anodic bars in various corrosive environments was determined and substituted into the Stern-Geary equation and Faraday's law to calculate the microcell corrosion rate. On the other hand, the Cr content of Cr-bearing rebars to meet the requirement for a service life of 100 years was calculated based on the service life of concrete members estimated by the above-mentioned process. Formulation of Diffusion/Penetration Rates of Corrosion FactorsMacrocell corrosion induced by cracking in cover concrete is caused by material nonuniformity resulting from the differences in the penetration rates of Cl Ϫ and CO 2 . For this reason, it is necessary first to determine the penetration rates of Cl Ϫ ...

“…(6) into Eq. (11). In this study, t st-in was assumed to be 75 d, the total period of corrosion-accelerating testing.…”

Section: Verification Of Microcell Corrosion Rate Model For Cr-bearinmentioning

confidence: 99%

“…[5][6][7][8] With this as a background, the authors have been investigating the corrosion resistance of Cr-bearing rebars having lower alloying elements, such as chromium, nickel, and molybdenum, than general stainless steel to allow production by processes similar to those of normal steel. [9][10][11][12] In this paper, a microcell corrosion rate model incorporating the corrosion attenuation phenomenon over time is formulated with the aim of developing Cr-bearing rebar having the required corrosion resistance in microcell corrosion environments. The service lives of reinforced concrete structures made using Cr-bearing rebars were then estimated based on the corrosion rate model.…”

Section: Introductionmentioning

confidence: 99%

Service Life Estimation of Reinforced Concrete Structures Made Using Cr-bearing Rebars in Microcell Corrosion Environments

Kyung

Ujiro³

et al. 2007

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Reinforced concrete structures made using Cr-bearing rebars subject to microcell corrosion were assumed with the aim of developing Cr-bearing rebars having the required corrosion resistance in microcell corrosion environments. Their service lives were then estimated for each type of corrosion environment based on a microcell corrosion rate model, and requirements for Cr-bearing rebars to achieve a service life of over 100 years were calculated. As a result, the service lives of concrete structures reinforced with Crbearing rebars were found to increase as the Cr content increased in all types of corrosion environments. Also, Cr-bearing rebars with Cr contents of not less than 11 % and not less than 7 % ensured service lives of over 100 years in harsh and moderate chloride attack zones, respectively. In carbonation zones, a Cr content of not less than 3 % was proven to provide corrosion resistance for over 100 years.