ACI 222R-2001 Protection of Metals in Concrete Against Corrosion《混凝土防腐金属的保护》.pdf

1、ACI 222R-01 supersedes ACI 222R-96 and became effective September 25, 2001.Copyright 2001, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, p

2、rinted, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors.222R-1ACI Committee Reports, Guides, and Commentaries areintended for guidance in planning, desig

3、ning, executing, andinspecting construction. This document is intended for the useof individuals who are competent to evaluate the significanceand limitations of its content and recommendations and whowill accept responsibility for the application of the material itcontains. The American Concrete In

4、stitute disclaims any andall responsibility for the stated principles. The Institute shallnot be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the

5、 contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.Protection of Metals in Concrete Against CorrosionReported by ACI Committee 222ACI 222R-01(Reapproved 2010)This report reflects the state of the art of corrosion of metals, andespecially reinf

6、orcing steel, in concrete. Separate chapters are devoted tothe mechanisms of the corrosion of metals in concrete, protective measuresfor new concrete construction, procedures for identifying corrosiveenvironments and active corrosion in concrete, and remedial measures.Keywords: admixture; aggregate;

7、 blended cement; bridge deck; calciumchloride; carbonation; cathodic protection; cement paste; coating; corrosion;corrosion inhibitor; cracking; deicer; deterioration; durability; parking struc-tures; polymers; portland cements; prestressed concrete; prestressing steels;protective coatings; reinforc

8、ed concrete; reinforcing steels; repairs; resins;resurfacing; spalling; waterproof coatings; zinc coatings.CONTENTSChapter 1Introduction, p. 222R-21.1Background1.2ScopeChapter 2Mechanism of corrosion of steel in concrete, p. 222R-32.1Introduction2.2Principles of corrosion2.3Reinforcing bar2.4The con

9、crete environmentChapter 3Protection against corrosion in new construction, p. 222R-93.1Introduction3.2Design and construction practices3.3Methods of excluding external sources of chloride ionfrom concrete3.4Corrosion control methodsChapter 4Procedures for identifying corrosive environments and acti

10、ve corrosion in concrete, p. 222R-184.1Introduction4.2Condition evaluation of reinforced concrete structures4.3Corrosion evaluation methods4.4Concrete evaluation test methodsTheodore Bremner John Grant Richard Montani Arpad SavolyJohn Broomfield Ping Gu Mahamad Nagi William ScannellKenneth Clear Tre

11、y Hamilton, III Theodore Neff Morris SchupackJames Clifton Kenneth Hover Keith Pashina Khaled SoudkiSteven Daily Thomas Joseph William Perenchio David TrejoMarwan Daye Mohammad Khan Randall Poston Thomas WeilEdwin Decker*David ManningRobert Price*Jeffrey WestRichard Didelot David McDonald D. V. Redd

12、y Richard WeyersBernard Erlin Edward McGettigan*DeceasedBrian B. HopeChairCharles K. NmaiSecretary222R-2 ACI COMMITTEE REPORTChapter 5Remedial measures, p. 222R-285.1Introduction5.2General5.3Applicability5.4The remedies and their limitations5.5SummaryChapter 6References, p. 222R-326.1Referenced stan

13、dards and reports6.2Cited references6.3Other referencesCHAPTER 1INTRODUCTION1.1BackgroundThe corrosion of metals, especially reinforcing steel, inconcrete has received increasing attention in recent years be-cause of its widespread occurrence in certain types of struc-tures and the high cost of repa

14、iring the structures. Thecorrosion of steel reinforcement was first observed in marinestructures and chemical manufacturing plants.1-3Recently,numerous reports of its occurrence in bridge decks, parkingstructures, and other structures exposed to chlorides havemade the problem particularly prominent.

15、 Extensive re-search on factors contributing to steel corrosion has in-creased our understanding of the mechanics of corrosion,especially concerning the role of chloride ions. It is anticipat-ed that the application of the research findings will result infewer instances of corrosion in new reinforce

16、d concretestructures and improved methods of repairing corrosion-in-duced damage in existing structures. For these improve-ments to occur, the research information should bedisseminated to individuals responsible for the design, con-struction, and maintenance of concrete structures. Concrete normall

17、y provides reinforcing steel with excel-lent corrosion protection. The high-alkaline environment inconcrete creates a tightly adhering film that passivates thesteel and protects it from corrosion. Because of concretesinherent protective attributes, corrosion of reinforcing steeldoes not occur in the

18、 majority of concrete elements or struc-tures. Corrosion of steel, however, can occur if the concretedoes not resist the ingress of corrosion-causing substances,the structure was not properly designed for the service envi-ronment, or the environment is not as anticipated or changesduring the service

19、 life of the structure.While several types of metals may corrode under certainconditions when embedded in concrete, the corrosion ofsteel reinforcement is the most common and is of the greatestconcern, and, therefore, is the primary subject of this report.Exposure of reinforced concrete to chloride

20、ions is the ma-jor cause of premature corrosion of steel reinforcement. Cor-rosion can occur, however, in some circumstances in theabsence of chloride ions. For example, carbonation of con-crete reduces concretes alkalinity, thereby permitting corro-sion of embedded steel. Carbonation is usually a s

21、lowprocess in concretes with a low water-cementitious materialsratio (w/cm). Carbonation-induced corrosion is not as com-mon as corrosion induced by chloride ions. Chloride ions are common in nature and very smallamounts are normal in concrete-making materials. Chlorideions may also be intentionally

22、 added into the concrete, mostoften as a constituent of accelerating admixtures. Dissolvedchloride ions may also penetrate hardened concrete in struc-tures exposed to marine environments or to deicing salts.The rate of corrosion of steel reinforcement embedded inconcrete is influenced by environment

23、al factors. Both oxy-gen and moisture must be present if electrochemical corro-sion is to occur. Reinforced concrete with significantgradients in chloride-ion content is vulnerable to macrocellcorrosion, especially when subjected to cycles of wettingand drying. This condition often occurs in highway

24、 bridgesand parking structures exposed to deicing salts and in struc-tures in marine environments. Other factors that affect therate and level of corrosion are heterogeneity in the concreteand the reinforcing steel, pH of the concrete pore water, car-bonation of the portland cement paste, cracks in

25、the concrete,stray currents, and galvanic effects due to contact betweendissimilar metals. Design features and construction practicesalso play an important role in the corrosion of embeddedsteel. Mixture proportions of the concrete, thickness of con-crete cover over the reinforcing steel, crack-cont

26、rol mea-sures, and implementation of measures designed specificallyfor corrosion protection are some of the factors that help con-trol the onset and rate of corrosion.Deterioration of concrete due to corrosion of the reinforc-ing steel results because the solid products of corrosion (rust)occupy a g

27、reater volume than the original steel and exertsubstantial expansive stresses on the surrounding concrete.The outward manifestations of the rusting include staining,cracking, and spalling of the concrete. Concurrently, thecross-sectional area of the reinforcing steel is reduced. Withtime, structural

28、 distress may occur either because of loss ofbond between the reinforcing steel and concrete due tocracking and spalling or as a result of the reduced steel cross-sectional area. This latter effect can be of special concern instructures containing high-strength prestressing steel inwhich a small amo

29、unt of metal loss could induce failure.Research on corrosion has not produced a carbon steel orother type of reinforcement that will not corrode when usedin concrete and which is both economical and technically fea-sible. Serious consideration is being given to the use of stain-less steel reinforcem

30、ent for structures exposed to chlorides4and several structures have been built using stainless steel. Inaddition, practice and research indicate the need for qualityconcrete, careful design, good construction practices, andreasonable limits on the amount of chlorides in the concretemixture ingredien

31、ts. Measures that are being used and furtherinvestigated include the use of corrosion inhibitors, protec-tive coatings on the reinforcing steel, and cathodic protection.In general, each of these measures has been successful. Prob-lems resulting from corrosion of embedded reinforcing steeland other m

32、etals, however, have not been eliminated.1.2ScopeThis report discusses the factors that influence corrosionof reinforcing steel in concrete, measures for protecting em-PROTECTION OF METALS IN CONCRETE AGAINST CORROSION 222R-3bedded reinforcing steel in new construction, techniques fordetecting corro

33、sion in structures in service, and remedialprocedures. Consideration of these factors and application ofthe discussed measures, techniques, and procedures shouldassist in reducing the occurrence of corrosion and result, inmost instances, in the satisfactory performance of reinforcedand prestressed c

34、oncrete structural members.CHAPTER 2MECHANISM OF CORROSION OF STEEL IN CONCRETE2.1IntroductionThis chapter describes the thermodynamics and kinetics ofthe corrosion of steel embedded in concrete. Subsequent sec-tions explain the initiation of active corrosion by chlorides,carbonation of the concrete

35、 cover, and the rate-controllingfactors for corrosion after it has been initiated. Finally, theinfluence of reinforcement type and of the concrete environ-ment are discussed.2.2Principles of corrosion2.2.1 The corrosion processThe corrosion of steel inconcrete is an electrochemical process; that is,

36、 it involves thetransfer of charge (electrons) from one species to another.For an electrochemical reaction to occur (in the absence ofan external electrical source) there must be two half-cell re-actionsone capable of producing electrons (the anodic re-action, the oxidation of iron, Fe, to form ferr

37、ous ions) andone capable of consuming electrons (the cathodic reaction,the reduction of oxygen to form hydroxyl ions, OH). Whenthe two reactions occur at widely separated locations, they aretermed a macrocell; when they occur close together, or essen-tially at the same location, they are termed a mi

38、crocell.For steel embedded in concrete, the anodic half-cell reac-tions involve the oxidation or dissolution of iron, namelyFe Fe+ + 2e (2.1a)2Fe+ + 4OH 2Fe(OH)2 (2.1b)2Fe(OH)2 + 1/2O2 2FeOOH + H2O (2.1c)Fe + OH + H2O HFeO2 + H2 (2.1d)and the most likely cathodic half-cell reactions are2H2O + O2 + 4

39、e 4 (OH) (2.2)2H+ + 2e H2 (2.3)Which of these anodic and cathodic reactions will actu-ally occur in any specific case depends on the availabilityof oxygen and on the pH of the cement paste pore solutionin the vicinity of the steel. This is shown by the Pourbaixdiagram,5 illustrated in Fig. 2.1, whic

40、h delineates thethermodynamic areas of stability for each of the species in-volved in the previously mentioned reactions as a function ofFig. 2.1Simplified Pourbaix diagram showing the poten-tial pH ranges of stability of the different phases of iron inaqueous solutions.5electrochemical potential* a

41、nd pH of the environment. Forthe reaction shown in Eq. (2.2) to occur, the potential mustbe lower than that indicated by the upper dashed line, whereasthe reaction shown in Eq. (2.3) can only proceed at potentialsbelow the lower dashed line. In general, if all other factorsare kept constant, the mor

42、e oxygen that is available, the morepositive (anodic) will be the electrochemical potential.For sound concrete, the pH of the pore solution ranges from13.0 to 13.5, within which the reactions shown in Eq. (2.la)and (2.1b) are the most likely anodic reactions. In the absenceof any other factors, the

43、iron oxides, Fe3O4 and Fe2O3 orhydroxides of these compounds, will form as solid phasesand may develop as a protective (passive) layer on the steel,described as follows. If the pH of the pore solution is reduced,for example, by carbonation or by a pozzolanic reaction, thesystem may be shifted to an

44、area of the Pourbaix diagram inwhich these oxides do not form a protective layer and activedissolution is possible. Theoretically, active corrosioncould also be induced by raising the pH to a value at whichthe reaction shown in Eq. (2.1d) can take place and forwhich HFeO2 is the thermodynamically st

45、able reactionproduct. The reaction shown in Eq. (2.1c) can also take placeat normal concrete pH at elevated temperatures ( 60 C,140 F).6 No examples of this reaction have been reported. 2.2.2 Nature of the passive filmA passive film can berelatively thick and inhibit active corrosion by providing a*

46、The electrochemical potential is a measure of the ease of electron charge transferbetween a metal and its environment, in this case, between the steel and the cementpaste pore solution. It is a property of the steel/concrete interface and not of the steelitself. It is not possible to determine the a

47、bsolute value of the potential and, therefore,it is necessary to measure the potential difference between the steel surface and a ref-erence electrode. This might be a standard hydrogen electrode (SHE), a saturatedcalomel electrode (SCE), or a Cu/CuSO4 electrode (CSE). The value of the potentialin a

48、 freely corroding system is commonly known as the corrosion potential, the opencircuit potential, or the free potential.222R-4 ACI COMMITTEE REPORTThe corrosion current can be converted to a rate of loss ofmetal from the surface of the steel by Faradays law(2.4)whereM = mass of metal dissolved or co

49、nverted to oxide, g; I = current, A; t = time, s; Aw= atomic weight; n = valency; and F = Faradays constant (96,500 coulombs/equivalent mass).By dividing by the density, the mass can be converted tothickness of the dissolved or oxidized layer, and for iron (orsteel): 1 A/cm2=11.8 m/yr. The current density, which isequivalent to the net current divided by the electrode area,however, cannot be determined directly. This is because therequirement of a charge balance means that the rates of pro-duction and consumption of elect