ACI 364.3T-2015 Treatment of Exposed Epoxy-Coated Reinforcement in Repair.pdf

1、ACI 364.3T-15TechNote1 TreaTmenT of exposed epoxy-CoaTed reinforCemenT in repairKeywords: coating; corrosion; corrosion inhibitor; electrical resistance; epoxy-coated; reinforcing bars; reinforcing steel; repair; ring anode effect; sacrificial anode.IntroductionThis document outlines the treatment a

2、nd repair of concrete areas containing epoxy-coated reinforcing steel when epoxy-coated reinforcing steel is exposed in a repair area.QuestionHow should reinforcement be treated when epoxy-coated reinforcement is exposed and damaged in a repair area before the concrete repair materials are placed?Si

3、gnificanceConcerns have been raised that the repair of structures containing epoxy-coated reinforcing steel may differ from structures containing uncoated reinforcing steel.AnswerStructures containing epoxy-coated reinforcing steel should be carefully repaired to avoid creating corrosion cells that

4、may result in accelerated corrosion of the reinforcement.DiscussionDuring concrete removal and preparation of the repair area, the epoxy coating on the bars within the repair will likely be damaged. The coating may have defects, or, as part of the repair procedure, it may be completely removed. Mini

5、mize the risk of accelerated corrosion-induced damage to the concrete, particularly in the areas surrounding the repair, by following the procedure presented herein.It is common practice to clean, prepare, and recoat any exposed epoxy-coated steel reinforcement during the repair process, usually wit

6、h an epoxy coating compatible with the existing fused coating on the steel. Consider additional protection because it is difficult to repair the damaged coating on the steel completely. Areas left uncoated or the presence of coating defects may result in an increase in the rate of corrosion of steel

7、 in the concrete surrounding the repair, due to the anodic ring effect, after the repairs are completed. However, any coating will reduce the corrosion rate compared to uncoated bars.When concrete repair is undertaken, chloride-contaminated or carbonated concrete is typically removed and replaced wi

8、th repair material within the repair area. In many cases, not all of the contaminated concrete is removed. After the repair, the reinforcing steel may be in contact with concrete outside the repair area having varying levels of contamination. Differences in pH and chloride ion concentrations between

9、 the new repair material and the remaining contaminated concrete will result in corrosion potential (voltage) differences. A current will flow as a result of these voltage differences, leading to anodic ring corrosion.Reinforcement locations surrounded by concrete with the highest moisture and chlor

10、ide contamination are likely to corrode first. Corrosion will occur in locations where there is both a defect in the coating and a suffi-cient level of contamination present. Generally, the corrosion rate is proportional to the ratio of the cathodic area to the anodic area. Because the surface area

11、of coated steel is often greater than the area of exposed steel, American Concrete Institute Copyrighted Material www.concrete.org2 TREATMENT OF EXPOSED EPOXY-COATED REINFORCEMENT IN REPAIR (ACI 364.3T-15)the rate of corrosion of the uncoated steel areas outside the repair can be high. Completing a

12、repair may also increase the area of uncoated steel within the repair area, particularly if the steel is not coated during the repair. As a result, corrosion of the steel immediately adjacent to the repair area at locations with defects or where the epoxy has delaminated will continue, and the corro

13、sion rate in these areas may increase compared with bars that are fully coated. The uncoated area of steel inside the repair area will contribute to the overall corrosion cell, which could result in corrosion of steel in the existing concrete in the locations where sufficient contamina-tion, oxygen,

14、 and moisture are present.In addition to coatings, other options exist to mitigate corrosion of concrete containing epoxy-coated bars. They include the use of nonmetallic reinforcement and cathodic protection systems (both impressed current and galvanic types), which are discussed in ACI 222R (ACI C

15、ommitte 222 2001) and ICRI 310.1R 2008. Provide supplemental corrosion protection for existing steel reinforcement by recoating the reinforcing bar, installing an appropriate high-electrical-resistance repair concrete, or using embedded galvanic anodes, as illustrated in Table 1. If a high-electrica

16、l-resistance repair concrete or mortar is used, a conductive mortar should be installed between the galvanic anodes and the substrate or the effectiveness of the galvanic anodes will be reduced. A combination of corrosion protection methods from Table 1 will usually provide better corrosion protecti

17、on than any individual method. Corrosion of the area surrounding the repair location may also be minimized by reducing the moisture content of the concrete, through the use of a breathable membrane or sealer.SummaryRepairs should be completed to minimize the corrosion of steel adjacent to the repair

18、 areas. The use of coat-ings on epoxy-coated reinforcing bars that are exposed during repair can be beneficial in reducing the surface area of steel available to promote corrosion. The use of high-electrical-resistance repair materials can reduce the corrosion current by increasing the circuit resis

19、tance. The use of embedded galvanic anodes can be benefi-cial in providing galvanic corrosion protection to portions of the steel where the epoxy coating is defective, either inside or adjacent to the repair. Treating exposed epoxy-coated reinforcing bars in repair areas is recom-mended to suppress

20、ongoing corrosion activity and mitigate the anodic ring effect adjacent to the repair area.ReferencesACI Committee 222, 2001, “Protection of Metals in Concrete against Corrosion (ACI 222R-01) (Reapproved 2010),” American Concrete Institute, Farmington Hills, MI, 41 pp.ACI Committee E706, 2005, “Inst

21、allation of Embedded Galvanic Anodes Field Guide to Concrete Repair Applica-tion Procedures (ACI RAP-8),” American Concrete Institute, Farmington Hills, MI, 6 pp. ICRI Guideline No. 310.1R-08 (formerly No. 03730), “Guide for Surface Preparation for the Repair of Deterio-rated Concrete Resulting from

22、 Reinforcing Steel Corrosion,” International Concrete Repair Institute, Rosemont, IL, 2008, 12 pp. American Concrete Institute Copyrighted Material www.concrete.orgTREATMENT OF EXPOSED EPOXY-COATED REINFORCEMENT IN REPAIR (ACI 364.3T-15) 3Table 1Supplemental corrosion protectionPrior to repairCorros

23、ion begins at defects in coating Initial corrosion of steel at defects in coating: cracking, delamination, and spalling resultRepair systems Benefits LimitationsBare steel inside patch repair Reinforcing steelCleaned inside repair, patch completed with cementitious mortarRequires minimal effort Leav

24、ing large area of exposed, passive steel in patch may greatly accelerate the corrosion at concen-trated points in the concrete next to the repair area (ring anode effect)Steel coated inside patch repair Reinforcing steelCleaned inside repair and recoatedReduces size of passive area of steel and redu

25、ces corrosion rateDifficult to coat the bar entirely, defects create passive areas of steel that may accelerate corrosion in the concrete next to patch (ring anode effect)Steel coating and high-resistance mortar Reinforcing steelCleaned and recoated, high-resistance mortar used to com-plete patchCom

26、bined protection, both the epoxy coat-ing and high-resistance mortar work to reduce local corrosion cellsCorrosion activity reduced compared to aforementioned options, but not haltedEmbedded galvanic anode Reinforcing steelCleaned and recoated (optional), embedded galvanic anodes at-tached to steel.

27、 Refer to ACI RAP Bulletin 8 for more information.Combined protection, epoxy coating (optional) reduces rate of corro-sion, galvanic anode also reduces corrosion in the crucial area next to the repairProtection depends on elec-trical continuity of reinforce-ment, protection diminishes with distance

28、from anodeAmerican Concrete Institute Copyrighted Material www.concrete.org4 TREATMENT OF EXPOSED EPOXY-COATED REINFORCEMENT IN REPAIR (ACI 364.3T-15)ACI TechNotes are intended for reference for the design and construction of concrete structures. This document is intended for the use of individuals

29、who are competent to evaluate the significance and limitations of its content and who will accept responsibility for the appli-cation of the information it contains. The American Concrete Institute disclaims any and all responsibility for the accuracy of the content and shall not be liable for any l

30、oss or damage arising therefrom. Reference to this document shall not be made in contract documents.ACI 364.3T-15 was adopted and published July 2015.Copyright 2015, American Concrete Institute.All rights reserved including the rights of reproduction and use in any form or by any means, including th

31、e making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.For additional c

32、opies, please contact: American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 Phone: +1.248.848.3700, Fax: +1.248.848.3701 www.concrete.orgReported by ACI Committee 364David A. VanOcker, Chair Marjorie M. Lynch, SecretaryRandall M. Beard Kal R. Hindo Alexander M. VaysburdB

33、enoit Bissonnette Charles J. Hookham James WarnerChristopher D. Brown Ashok M. Kakade David W. WhitmoreRyan Alexander Carris Keith E. KesnerLarry D. Church Erick N. Larson Consulting MembersBruce A. Collins John S. Lund Robert V. GeveckerBoris Dragunsky Pritpal S. Mangat Stephen A. JohansonPaul E. G

34、audette Surendra K. Manjrekar Emory L. KempTimothy R. W. Gillespie James E. McDonald Howard H. Newlon Jr.Fred R. Goodwin Jay H. Paul Weilan SongZareh B. Gregorian Murat B. Seyidoglu Dela TharmabalaPawan R. Gupta K. Nam Shiu Robert TracyJohn L. Hausfeld Thomas E. Spencer William F. WescottRobert L. Henry Valery Tokar