Effect of Cathodic Protection on Epoxy-coated Rebar

Effect of Cathodic Protection on Epoxy-coated Rebar
Author: S. Ray Taylor
Publisher:
Total Pages: 66
Release: 1998
Genre: Epoxy coatings
ISBN:

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Epoxy coating is widely used to mitigate the access of chloride ions to the surface of a rebar. However, corrosion at the point of physical defects in the coating necessitates rehabilitation. Based on its effectiveness in mitigating corrosion of uncoated rebars, we examined cathodic protection (CP) as a method for rehabilitating epoxy-coated rebars (ECR). Although it is well established that cathodic polarization of epoxy coatings on steel in aqueous conditions leads to disbondment of the coating, neither the conditions that lead to this phenomenon nor the actual occurrence of this disbondment process has been determined for ECR in concrete. Since the integrity of the bond between the rebar and the concrete is essential to the composite strengthening by the rebar, the relationships among CP, the integrity of the epoxy coating, and the strength of the rebar/concrete bond must be investigated. The objectives of this study were (1) to determine if CP can effectively mitigate corrosion of coated rebar without adversely affecting the rebar/concrete interface, and (2) to examine the effect of cathodic polarization on the disbonding characteristics of the epoxy coating/rebar interface in concrete. Fifty-five samples of No. 5 ECR with coating defects were exposed to CP. Tensile loading produced splitting failures of all samples. This mode of failure allows greater sensitivity to the contributions of concrete/rebar adhesion and friction than do pullout failures. All electrochemical tests indicated that the cathodic polarization levels and times of application used in this study were effective in preventing corrosion of embedded ECR. An important finding was that the CP protection levels and times had no effect on the splitting failure characteristics based on comparisons of 95 percent confidence intervals. Multiple parameters within the electrochemical impedance spectra indicated that the epoxy coating was delaminating from the steel at the periphery of the defects. This phenomenon was verified in a post mortem analysis of the samples using scanning electron microscopy. The immediate significance of this result is that CP current demands could increase over time. Even though the levels of delamination in this study did not affect mechanical performance, a protective CP level that does not induce film delamination should be explored.

Corrosion Protection of Reinforcing Steels

Corrosion Protection of Reinforcing Steels
Author: fib Fédération internationale du béton
Publisher: fib Fédération internationale du béton
Total Pages: 123
Release: 2009-01-01
Genre: Technology & Engineering
ISBN: 2883940894

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It has long been recognised that corrosion of steel is extremely costly and affects many industry sectors, including concrete construction. The cost of corrosion of steel reinforcement within concrete is estimated at many billions of dollars worldwide. The corrosion of steel reinforcement represents a deterioration of the steel which in turn detrimentally affects its performance and therefore that of the concrete element within which it has been cast. A great amount of work has been undertaken over the years concerning the prevention of corrosion of steel, including the application of coatings, which has included the study of the process of corrosion itself, the properties of reinforcing steels and their resistance to corrosion as well as the design of structures and the construction process. The objective of fib Bulletin 49 is to provide readers with an appreciation of the principles of corrosion of reinforcing steel embedded in concrete and to describe the behaviour of particular steels and their coatings as used to combat the effects of such corrosion. These include galvanised reinforcement, epoxy coated reinforcement, and stainless reinforcing steel. It also provides information on the relative costs of the materials and products which it covers. It does not deal with structure design or the process of construction or with the post-construction phase of structure management including repair. It is hoped that it will nevertheless increase the understanding of readers in the process of corrosion of reinforcing steels and the ability of key materials and processes to reduce its harmful effects.

Coating Protection for Reinforcement

Coating Protection for Reinforcement
Author: C. Andrade
Publisher: Thomas Telford
Total Pages: 64
Release: 1995
Genre: Concrete coatings
ISBN: 9780727720214

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This report provides a technical survey of the most common coating protection systems for steel reinforcement, the use of which is rapidly increasing at present. The text also evaluates the practical effect of the systems and is the result of a research project conducted by a CEB task group which was specifically assembled to address the need for more information in this subject area.

Parameters Governing the Corrosion Protection Efficiency of Fusion-bonded Epoxy Coatings on Reinforcing Steel

Parameters Governing the Corrosion Protection Efficiency of Fusion-bonded Epoxy Coatings on Reinforcing Steel
Author:
Publisher:
Total Pages: 67
Release: 2008
Genre: Cathodic protection
ISBN:

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The purpose of this study was to investigate various epoxy coating and exposure parameters to determine their effects on the corrosion of reinforcing steel. The parameters investigated were: chloride content at the bar depth, coated bar corroded area, corrosion product color under the coating, epoxy coating adhesion, coating color, coating damage (holidays and holes), coating thickness, TGA, DSC and EDS analysis and SEM coating cracking investigation. This study demonstrated that the ECR coating samples extracted from concrete exhibited extensive cracking compared to the new ECR samples in which the coating cracking was limited to only one sample. The coating cracking correlated with the amount of chloride at bar level, residual adhesion of the epoxy to the steel surface, and the percent moisture in the coating. The coating cracking is also related to the change in color of the epoxy and indicates that the epoxy coating degradation in concrete influences the surface condition of the coating. The DSC results showed that both the extracted epoxy coating samples as well as new samples are not fully cured during the manufacturing process. Additionally, the extracted epoxy coated samples investigated presented significant permanent adhesion loss with little or no epoxy coating residue present on the bar surface, while the EDS analysis showed that once adhesion is lost, corrosion will proceed unimpeded under the coating even in the absence of chlorides. The parameters that presented a direct correlation with the observed corrosion activity were the number of holidays and the number of damaged areas per unit length of bar. The results also show a distinct loss of quality control in the handling and possibly storage of new coated bars. The new ECR samples had significantly higher damage density than the samples extracted from concrete, while there was no change in the number of holidays and cure condition.

Cathodic Protection of Steel in Concrete and Masonry

Cathodic Protection of Steel in Concrete and Masonry
Author: Paul M. Chess
Publisher: CRC Press
Total Pages: 250
Release: 2015-02-04
Genre: Technology & Engineering
ISBN: 0203938070

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Revised and updated, this second edition of Cathodic Protection of Steel in Concrete and Masonry covers both reinforced concrete and masonry structures, describes in detail the overall design factors involved in cathodic protection (CP), and also provides a theoretical basis for why it works. It refers to the new European standard EN 12696 for cath

Effect of Accelerated Corrosion on the Bond Strength of Corrosion Resistant Reinforcing Bars Embedded in Concrete

Effect of Accelerated Corrosion on the Bond Strength of Corrosion Resistant Reinforcing Bars Embedded in Concrete
Author: Sourav Khatua
Publisher:
Total Pages:
Release: 2017
Genre: Adhesives
ISBN:

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Corrosion of steel reinforcing bars embedded in concrete applications is a major problem all over the world. Effect of corrosion causes metal loss at sections, cracks in the concrete surrounding the reinforcing steel, spalling of cover concrete also leads to de-bonding of reinforcing bar from the concrete. Corrosion cracks in the surrounding concrete leads to loss in bond strength and finally reduce the structural strength and service life of the structure. This problem is consistently observed in structural slab bridges that are exposed to deicing salts during the winters. In the era of 1980's, black convention steel was replaced with epoxy-coated bars as a solution to prevent corrosion in bridge decks. However the advantage of using epoxy coated bars is still uncertain as the bond strength of these type of bars is a concern. Several researchers in the past have highlighted deleterious effect of corrosion on epoxy-coated bars that are damaged during handling. It is necessary to study the use of alternative reinforcing bars as means of corrosion protection in bridge deck applications. There are several corrosion resistant bars that are readily available in the market, but performance of these bars under accelerated corrosion conditions is still unclear. Six different types of bars which include, conventional black bars, epoxy-coated bars, hot dipped galvanizing bars, continuously galvanized bars, stainless steel bars and MMFX bars were studied in this thesis. The objective of this study is to investigate the effect of accelerated corrosion on bond strength of concrete. The bond between concrete and reinforcement bars play a major role in transfer of stresses from concrete to steel. However, corrosion weakens this bond, resulting in weakening of the Reinforced Concrete member. So, it was necessary to investigate the performance of CRR (Corrosion Resistant Bars) embedded in concrete and s ubjected to accelerated corrosion. The effect of addition of polypropylene fibers on the bond strength was studied. A total of 48 prism specimens were cast with CRR bars including the ones with fibers, of which 24 specimens were subjected to accelerated corrosion. The prisms were 6-inch cube with a reinforcing bar at the centre of each specimen. The embedment length of the bar was 2.5 inches at the mid-height of the section. An electrochemical cell was adopted by placing the specimens in a tank containing 5% salt solution with stainless steel cathode surrounding the specimen. The circuit was completed by connecting the cathode and the reinforcing bar to an external power supply. The specimens were subjected to accelerated corrosion for total of 21 days which includes a two-day wetting and one day drying cycle. Impressed current of 0.02A, calculated using Faraday's law to achieve 5% corrosion damage was supplied during the wetting cycle using external power source. The corroded specimens were then tested to investigate the loss of bond strength due to corrosion and capture any improvement in bond strength using polypropylene fibers. It was observed that, corrosion of bars showed serious bond loss leading to reduced pull-out strength with larger slip of the bars relative to the embedded concrete prisms. Addition of polypropylene fibers showed an improvement in the overall performance of the corroded specimens by increasing the load capacity, reducing slip and improving failure mode from brittle to more ductile mode, compared to un-corroded specimens..