1、Report on Corrosion of Prestressing SteelsReported by ACI Committee 222ACI 222.2R-14First PrintingOctober 2014ISBN: 978-0-87031-923-5Report on Corrosion of Prestressing SteelsCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced
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11、).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis report covers various types of prestressing steel, including some discussion on metallurgical differences, and supplements information presented in ACI 222R t
12、o include topics specifically related to prestressing steels. Deterioration mechanisms are discussed, including hydrogen embrittlement and stress-corrosion cracking. Methods to protect prestressing steel against corrosion in new construction are presented, along with a discussion of field performanc
13、e of prestressed concrete structures. Finally, field evaluation and remediation techniques are presented. Appendixes present detailed information on stress-corrosion cracking and hydrogen embrittlement issues in prestressed concrete and mitiga-tion techniques.Keywords: anchorage; bonded; corrosion;
14、duct; durability; grout; hydrogen embrittlement; post-tensioned; prestressed; tendon; strand; stress-corrosion cracking; unbonded.Mohammad S. Khan, ChairACI 222.2R-14Report on Corrosion of Prestressing SteelsReported by ACI Committee 222Antonio J. Aldykiewicz Jr.Michael C. BrownDavid DarwinMarwan A.
15、 DayeStephen D. DischHamid FarzamPer FidjestolDavid P. GustafsonH. R. Trey Hamilton IIICarolyn M. Hansson*William G. HimeBrian B. HopeBurkan IsgorTracy D. Marcotte*David B. McDonaldRobert MoserTheodore L. NeffCharles K. NmaiKeith A. PashinaRandall W. Poston*Ruben M. SalasArpad SavolyAndrea J. Schokk
16、er*Morris SchupackKhaled A. SoudkiPaul G. TourneyDavid TrejoYash Paul VirmaniJeffrey S. West*Richard E. WeyersDavid W. WhitmoreConsulting MemberRichard O. LewisACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. Th
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18、y for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be rest
19、ated in mandatory language for incorporation by the Architect/Engineer.ACI 222.2R-14 supercedes ACI 222.2R-01 and was adopted and published October 2014.Copyright 2014, American Concrete InstituteAll rights reserved including rights of reproduction and use in any form or by any means, including the
20、making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual repro-duction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.*Subcommittee mem
21、berCONTENTSCHAPTER 1INTRODUCTION, p. 21.1Background, p. 21.2Scope, p. 3CHAPTER 2DEFINITIONS, p. 3CHAPTER 3PRESTRESSING STEELS, p. 33.1Wire, p. 33.2Strand, p. 33.3Bar, p. 3CHAPTER 4DETERIORATION OF PRESTRESSING STEELS, p. 4CHAPTER 5PROTECTION AGAINST CORROSION IN NEW CONSTRUCTION, p. 55.1Introduction
22、 and history, p. 55.2Prestressing tendon materials selection, p. 55.3Corrosion protection for prestressing systems, p. 85.4Cathodic protection, p. 14CHAPTER 6FIELD EVALUATION, p. 146.1Introduction, p. 146.2Evaluation goals, p. 146.3Pretensioned structures, p. 146.4Post-tensioned structures, p. 17CHA
23、PTER 7REMEDIATION TECHNIQUES, p. 207.1Introduction, p. 207.2General, p. 207.3Bonded post-tensioned tendons, p. 207.4Unbonded multistrand post-tensioned tendons, p. 221CHAPTER 1INTRODUCTION1.1BackgroundSeveral attempts were made to prestress concrete in the 1800s, but modern development of prestresse
24、d concrete began in 1928 and is credited to E. Freyssinet of France (Lin and Burns 1981). Freyssinet understood the importance of prestressing using high-strength steel to avoid prestressing losses that significantly reduce the applied prestressing force. Use of prestressed concrete began in the Uni
25、ted States with circular-wrapped prestressed tanks in 1941 (Schupack 1964). The first prestressed segmental concrete bridge in the United States was constructed in Madison County, TN, and opened to the public on October 28, 1950 (Bennett et al. 2002). The Walnut Lane Memorial Bridge, located in Penn
26、-sylvania, was completed in the fall of 1950 (Manning 1988). Applications of prestressing in bridge and building construc-tion then spread rapidly and have proven to be a successful construction method. Prestressed concrete construction enhances structural efficiency, improves control of flexural cr
27、acking, and allows for structural members with reduced dimensions.Although corrosion is not as well documented in prestressed concrete structures as in nonprestressed concrete structures, prestressed concrete members have a number of advan-tages regarding corrosion performance over conventional nonp
28、restressed concrete elements. In general, prestressed concrete construction follows higher-quality control prac-tices and material standards than conventional nonpre-stressed construction. These practices result in improved concrete properties that limit diffusion of chloride, which is further reduc
29、ed in prestressed concrete members due to absence or reduced-level cracking. Corrosion of prestressed concrete structures appears to be restricted to specific circumstances, including improper design, construction details, and construction practices. The potential for accel-erated corrosion still ex
30、ists in environments contaminated with chloride ions and hydrogen sulfide and it is impera-tive to protect prestressing steel. Corrosion of prestressing steel in bridges and buildings may not display outward signs of corrosion. Because failure of prestressing tendons could compromise the integrity o
31、f the structure, structures subjected to corrosive conditions should be periodically inspected with specific attention focused on the condition of the prestressing system.A number of surveys provide information concerning the potential for corrosion of prestressed structures. Burdekin and Rothwell (
32、1981) summarized practice, specifications, and corrosion mechanisms (1981) and reported that failure to provide adequate structural details and follow proper construction practices, as well as use of low-quality mate-rials, account for the vast majority of poor performance. Schupack reached similar
33、conclusions in additional surveys (Schupack 1978a, 1994; Schupack and Suarez 1982). More recently, corrosion problems were discovered in grouted post-tensioned bridges (Poston et al. 2003; Hartt and Venu-gopalan 2002; Muszynski 2003). The problems were largely attributed to inadequate post-tensionin
34、g details and grouting practices and deficient grout materials that led to accumula-tion of bleedwater voids.Because corrosion in prestressed concrete members can potentially result in fracture-critical modes of failure, more information needs to be developed, disseminated, and used. The magnitude o
35、f the corrosion problem, its projected extent, and measures that can resolve it are of vital concern to designers, contractors, and owners, and form the basis of this report.Prestressed concrete is used in several types of construc-tion and is described as either pretensioned or post-tensioned, depe
36、nding on whether the tendons are stressed before (pre) or after (post) the concrete is placed. Pretensioned concrete refers to systems in which high-strength wires or strands are stressed in forms between bulkheads before placement of the concrete. Concrete is cast and allowed to cure to a specified
37、 strength. Because the prestressing steel is bonded with the concrete, when the steel is released from the bulkheads, the concrete is placed in compression to equilibrate the tensile forces present in the steel. Pretensioning is common practice for both standardized precast bridge girders and in pre
38、cast structural building members, such as solid joists, solid and hollow-core planks, and single- and double-tee joists.Post-tensioned concrete refers to systems in which the concrete is placed and allowed to cure to a specified strength before prestressing. Post-tensioning is applied using either b
39、onded or unbonded tendons. Bonded post-tensioning requires that tubes or ducts with deformations be placed in CHAPTER 8FIELD PERFORMANCE OF PRESTRESSED CONCRETE STRUCTURES, p. 248.1Introduction, p. 248.2Corrosion of prestressing strand before construction, p. 258.3Pretensioned structures, p. 268.4Un
40、bonded post-tensioned structures, p. 278.5Bonded post-tensioned structures, p. 298.6Wire-wrapped prestressed structures, p. 31CHAPTER 9REFERENCES, p. 31APPENDIX APRESTRESSING STEEL METALLURGY , p. 37A.1Wire, p. 37A.2Strand, p. 38A.3Bar, p. 38APPENDIX BDETERIORATION OF PRESTRESSING STEEL, p. 38B.1Met
41、allurgy of prestressing steels, p. 38B.2Stress-corrosion cracking and hydrogen embrittle-ment, p. 39B.3Case histories, p. 40B.4Stress-corrosion cracking, p. 41B.5Hydrogen embrittlement, p. 43B.6Corrosion effect on fatigue performance, p. 47B.7Testing for SCC and HE, p. 47American Concrete Institute
42、Copyrighted Material www.concrete.org2 REPORT ON CORROSION OF PRESTRESSING STEELS (ACI 222.2R-14)the forms before concrete placement. After the concrete is placed and cured to a specified strength, bundles of strands, wires, or bars in the ducts are stressed against and anchored to the concrete. The
43、se bundles are called tendons.In the case of bonded tendon, after tendons have been installed and stressed and concrete has been placed and reached a strength such that tendon stressing can be performed, a grout that is a mixture of portland cement, water, and admixtures is pumped into the ducts. Du
44、cts can be metallic or nonmetallic and include uncoated or coated steel, high-density polyethylene (HDPE), and polypro-pylene. The grout fills spaces among the individual tendon strands, wires, or bars and between the tendon and duct. The grout provides two benefits: corrosion protection for the ten
45、don with the highly alkaline environment provided by the grout, and bond between the concrete and the tendon. Bonded prestressing is popular in bridges, buildings, dams, tanks, and tie-backs, and may be used with both precast and cast-in-place concrete construction.Unbonded post-tensioning commonly
46、uses single-strand tendons. Each strand is surrounded by an individual sheath and the annular space is filled with a post-tensioning coating (grease or wax) that inhibits corrosion and reduces friction between prestressing steel and sheathing. The tendon is installed in the formwork before placement
47、 of concrete. The sheath provides a barrier between the coated strand and the concrete, and allows the strand to be stressed after concrete placement. Usually, anchorages are cast into the concrete along with the tendon. Unbonded multistrand tendons have been used extensively in nuclear pressure ves
48、sels. Multiple wires or strands are placed in a cast-in-place duct that is usually filled with heated, corrosion-inhibiting, wax-like hydrophobic grease.Prestressing bars are widely used in bonded post-tensioning of liquid-containing tanks, in geotechnical appli-cations such as foundation tie-downs
49、and foundation wall tie-backs, and in segmental bridge construction.Prestressing wire is used in the construction of prestressed concrete tanks and the manufacture of concrete pipe. In tank construction, the wire under tension is wrapped around the tank circumference. This provides a circumferential compressive prestressing force that resists the radial tensile stresses developed by filling the tank. Prestressed concrete pipe is manufactured in a similar manner where the pipe is wound with high-strength prestressing wire.1.2ScopeThis repo
