ACI 423 8R-2010 Report on Corrosion and Repair of Grouted Multistrand and Bar Tendon Systems.pdf

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1、ACI 423.8R-10Reported by Joint ACI-ASCE Committee 423Report on Corrosion and Repairof Grouted Multistrandand Bar Tendon SystemsReport on Corrosion and Repairof Grouted Multistrand and Bar Tendon SystemsFirst PrintingOctober 2010ISBN 978-0-87031-395-0American Concrete InstituteAdvancing concrete know

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10、btained by contacting ACI.Most ACI standards and committee reports are gathered together in the annually revised ACI Manual ofConcrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgACI 423.8R-10 w

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14、onsibility for the stated principles. The Instituteshall not 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 contract documents, theyshall be

15、 restated in mandatory language for incorporation bythe Architect/Engineer.Report on Corrosion and Repair of Grouted Multistrand and Bar Tendon SystemsReported by Joint ACI-ASCE Committee 423ACI 423.8R-10This report gives general information regarding the evaluation of corrosiondamage in structures

16、reinforced with grouted multistrand and bar tendons.A review of current practice is included along with the historical back-ground. Specific potential problem areas for grouted tendons are discussedfor each critical part of the tendon. Current methods for evaluating corro-sion damage and typical rep

17、air schemes are included.Keywords: anchorage; bonded; corrosion; duct; durability; grout; post-tensioning; prestressed; repair; strand; tendon.CONTENTSChapter 1Introduction, p. 21.1General1.2Background1.3Scope1.4LimitationsChapter 2Definitions, p. 2Chapter 3Review of current practice, p. 33.1General

18、3.2Grouting requirements3.3Tendon protection requirementsChapter 4Grouted tendons, p. 44.1Evolution of grouted tendons4.2Types of grouted tendons4.3Potential problem areas4.4Duct4.5Grout4.6Strand and bar4.7Anchorage hardware and protection4.8Performance recordChapter 5Evaluating corrosion damage, p.

19、 75.1General5.2Monitoring5.3Nondestructive methods5.4Exploratory methodsChapter 6Repair schemes and methods, p. 96.1General6.2Grouting of voids6.3Tendon repairTheresa M. Ahlborn Henry J. Cronin Jr. Mohammad Iqbal Thomas C. SchaefferRobert W. Barnes Charles W. Dolan L. S. Paul Johal Andrea J. Schokke

20、rFlorian G. Barth James P. Donnelly Donald P. Kline Morris SchupackSarah L. Billington Martin J. Fradua Mark E. Moore Richard W. StoneAllan P. Bommer William L. Gamble Antoine E. Naaman Amy M. Reinke TrygestadKenneth B. Bondy Shawn P. Gross Theodore L. Neff H. Carl WalkerNed H. Burns Pawan R. Gupta

21、Sami H. Rizkalla Paul ZiaSteven R. Close H. R. Trey Hamilton III David H. SandersBruce W. RussellChairCarin L. Roberts-WollmannSecretary2 REPORT ON CORROSION AND REPAIR OF GROUTED MULTISTRAND AND BAR TENDON SYSTEMS (ACI 423.8R-10)American Concrete Institute Copyrighted Materialwww.concrete.orgChapte

22、r 7References, p. 97.1Cited referencesCHAPTER 1INTRODUCTION1.1GeneralThis report is intended to provide general information onthe corrosion and repair of grouted multistrand and bartendon systems. The information is intended to represent thestate of knowledge of the committee in the areas of corrosi

23、onprevention in grouted tendons, as well as evaluation andrepair. It is not intended as a standard or recommended practice.A strong background in durability of grouted post-tensioningsystems, including practical experience and training, isrecommended before designing, constructing, evaluating, orrep

24、airing these structures.This report focuses on the unique materials and hardwareassociated with grouted post-tensioning tendons. Generalcorrosion theory for metals in structural concrete systems isnot within the scope of this report. Information on corrosiontheory and mechanisms can be found in ACI

25、222R-01 andACI 222.2R-01.1.2BackgroundThe use of grouted high-strength wire, strand, and bar post-tensioning tendons as a viable construction technique began inNorth America in the 1950s. Components of the standardsystem have changed significantly over the last half-centuryfrom shimmed button-head w

26、ire-type systems to bundles ofseven-wire strand systems with wedges (Post-TensioningInstitute 2006). Post-tensioning bars may also be used ingrouted systems, although they have not changed significantlysince their first introduction. The latest generation of post-tensioning systems includes multiple

27、 layers of corrosionprotection due to an increased awareness of the importance ofa durable system.Grout material has also undergone significant changesover the past 50 years. For the majority of this time, a standardmixture of water and portland cement was used. Sometimeschemical admixtures were inc

28、luded to increase pumpabilityor to introduce expansion in an attempt to counteract settlementand voids. As early as the 1960s (Schupack 1971), it wasrecognized that bleed was a problem in grouts, which couldcause significant voids in the tendon. In the 1970s, an anti-bleedadmixture (Schupack 1973) w

29、as developed to reduce thebleeding tendencies of grouts. This formulation was usedsuccessfully in a number of major structures, but did not seewidespread use in the post-tensioning bridge and buildingindustries. During the late 1990s and early 2000s, prepackagedgrout formulations containing anti-ble

30、ed admixtures gainedsignificant popularity in the U.S. and continue to see wide-spread use. A sudden change in grouting materials in the late1990s was primarily due to the discovery of several post-tensioned bridges in Florida that had tendon corrosion (CorvenEngineering, Inc. 2001). Past performanc

31、e of grouted post-tensioning systems is covered in more detail in Section 4.1.Most layers of corrosion protection for post-tensioningsteel have seen significant advances in the last 5 to 10 years.The discovery of corrosion problems has also led to morestandardized methods for the evaluation of corro

32、siondamage and repair methods.1.3ScopeThis report includes a review and summary of the following:Guide specifications and training as applied to groutedpost-tensioning tendons;Potential problem areas in grouted systems;Durability enhancements for each component of thetendon;Evaluation of corrosion p

33、roblems; andRepair methods for grouted systems.1.4LimitationsThis report presents a summary of the typical problemsthat may occur in grouted post-tensioning systems andincludes guidelines for evaluation and repair. The material isgeneral in nature and may not apply to every situation. Dueto the uniq

34、ueness of each post-tensioned structure, engineeringjudgment must be used to determine the appropriate actionbased on experience and the general guidance provided inthis document.This report is not intended to be included as part of aspecification document for materials, evaluations, or repairs.Eval

35、uation of grouted post-tensioned tendons is a difficultundertaking and no single method can be used to fullydescribe the damage or life expectancy of a tendon. Due tothe many changes in materials and equipment over the last50-plus years, the evaluator may encounter a wide variationin the types of sy

36、stems encountered. Varying climates,environments, and the structures usage and design also playa role in possible deterioration. The evaluator must beknowledgeable about the performance of similar structuresunder similar conditions to get an indication, if any, ofinternal damage of the structure.CHA

37、PTER 2DEFINITIONSACI provides a comprehensive list of definitions throughan online resource, “ACI Concrete Terminology,” http:/terminology.concrete.org. Definitions provided hereincomplement that resource.admixturea material other than water, aggregates,cementitious materials, and fiber reinforcemen

38、t, used as aningredient in a cementitious mixture to modify its freshlymixed, setting, or hardened properties and that is added tothe batch before or during its mixing.admixture, water-reducingan admixture that eitherincreases slump of freshly mixed mortar or concrete withoutincreasing water content

39、 or maintains slump with a reducedamount of water, the effect being due to factors other than airentrainment.backflowa condition whereby the grout front reversesdirection and flows back on top of the grout layer in thebottom of the duct.bleedthe autogenous flow of mixing water within, or itsemergenc

40、e from, a newly placed cementitious mixturecaused by the settlement of solid materials within the massand filtering action of strands and wires.REPORT ON CORROSION AND REPAIR OF GROUTED MULTISTRAND AND BAR TENDON SYSTEMS (ACI 423.8R-10) 3American Concrete Institute Copyrighted Materialwww.concrete.o

41、rgcementitious materialsmaterials having cementingproperties.corrosion inhibitora chemical compound, either liquidor powder, usually intermixed in concrete and sometimesapplied to concrete, and that effectively decreases corrosionof steel reinforcement.ducta conduit (plain or corrugated) to accommod

42、ateprestressing steel for post-tensioned concrete.fluiditya measure of time, expressed in seconds,necessary for a stated quantity of grout to pass through theorifice of the flow cone.grouta mixture of cementitious material and water,with or without aggregate, proportioned to produce a pour-able cons

43、istency without segregation of the constituents;injected into the duct to fill the space around the tendon.high-range water-reducing admixturesee admix-ture, water-reducing.inlettubing or duct used for injection of grout into duct.outlettubing or duct to allow the escape of air, water,grout, and ble

44、ed water from the duct.post-tensioningmethod of prestressing in whichprestressing steel is tensioned after concrete has hardened.setthe condition reached by a cement paste, mortar, orconcrete when it has lost plasticity to an arbitrary degree,usually measured in terms of resistance to penetration or

45、deformation; initial set refers to first stiffening; final setrefers to attainment of significant rigidity; also, strainremaining after removal of stress.set timethe lapsed time from the addition of mixing waterto a cementitious mixture until the mixture reaches a specifieddegree of rigidity as meas

46、ured by a specific procedure.steel, prestressinghigh-strength steel used to prestressconcrete, commonly seven-wire strands, single wires, bars,rods, or groups of wires or strands.tendonan assembly consisting of a tensioned element(such as a wire, bar, rod, strand, or a bundle of theseelements) used

47、to impart compressive stress in concrete,along with any associated components used to enclose andanchor the tensioned element.thixotropica reversible, time-dependent decrease inviscosity when a fluid is subjected to increased shear stressor shear rate.vacuum groutinga process by which a partial vacu

48、umis generated within a void to create a pressure differentialthat allows grout to flow into and substantially fill the voidthrough a single grout inlet.volume changean increase or decrease in volume due toany cause.CHAPTER 3REVIEW OF CURRENT PRACTICE3.1GeneralCode requirements in the area of post-t

49、ensioning dura-bility were very minimal prior to publication of the Post-Tensioning Institutes (PTI), “Specification for Grouting ofPost-Tensioned Structures,” in 2001 (current editionpublished in 2003 PTI Committee on Grouting Specifica-tions 2003). This comprehensive document focuses ongrouting, including materials, construction, and testing, withemphasis on new construction.The American Segmental Bridge Institute (ASBI) establisheda Grouting Certification Program in 2001. The programformat, which includes both lecture and l