1、1ACI 364.10T-14Rehabilitation of StRuctuRe with ReinfoRcement Section loSSKeywords: concrete cover; corrosion; load-carrying capacity; rehabilitation; reinforcement; repair.IntroductionIntegrity of reinforcement is fundamental to the strength, ductility, and safety of reinforced concrete structures.
2、 Determining the necessity of additional or replacement reinforcement is a primary concern in rehabilitation projects containing corrosion of reinforcing steel.QuestionHow should an engineer address exposed and corroded rein-forcement when repairing a conventionally reinforced concrete structure (Fi
3、g. 1), and should there be a concern if the loss of reinforcement is less than 10 percent of the cross-sectional area?AnswerAfter determining the condition of the reinforcement, remove unsound concrete, clean reinforcement, and provide additional reinforcement as needed. The structural consequences
4、of a 10 percent cross-sectional area loss due to corrosion are usually minor for nonprestressed concrete components because there are usually redundancies in design.DiscussionBegin by identifying the source, extent and level of activity of reinforcement corrosion (ICRI No. 310.1R; ACI 364.6T), and d
5、eter-mining the overall condition and cross-sectional area of the affected reinforcing steel. Remove all unsound concrete; undercut the exposed corroded bars to provide clearance for under-bar cleaning and full bar embedment in the repair material; and secure the repair structurally, so as to ensure
6、 the required load-carrying capacity is achieved (Fig. 2). The clear space behind the reinforcing steel should be greater than 1/4 in. (6 mm), plus the dimension of the maximum-sized aggregate in the repair material (ACI 364.6T). Generally, a 3/4 to 1 in. (20 to 25 mm) gap is required to inspect and
7、 clean the bar. Place the repair material and encapsulate the bar with it.Clean the reinforcement by means of wire brushing, sandblasting, shot-blasting, or water-blasting. Do not use solvents as they can penetrate the concrete, which may create a poor bond surface for repair materials. If the reinf
8、orcing bars are epoxy-coated, the epoxy in the area surrounding the exposed corrosion should be removed and the bar cleaned.Measure the cross section. Use calipers to measure the reduced diameter of the reinforcing steel. If the loss of cross-sectional area is greater than 10 percent, additional (su
9、pplemental) reinforcement may be required (Fig. 3). If corro-sion pits with depths greater than 25 percent of the bar diameter are observed, additional reinforcement could also be required.The structural consequences of a 10 percent cross-section area loss due to corrosion are usually minor for nonp
10、re-stressed concrete components because of redundancies in design, as discussed in items (a) through (c) as follows. In practice, there is usually no concern with less than 10 percent loss of cross-sectional area.(a) Reinforcement reserveSteel reinforcement used in construction is typically larger t
11、han required by structural considerations. Extra steel is attributed to varying practical design requirements such as bar layout and spacing. Five to 10 percent more steel area is typically provided than is required by analysis.(b) Corrosion locationCorrosion damage is often uneven throughout the me
12、mber length and frequently may be at Fig. 1Example of severe reinforcing steel deterioration due to corrosion in a reinforced concrete beam (courtesy of the Ministry of Transportation of Quebec).TechNote2Fig. 2ICRI recommendations for cleaning and undercutting of reinforcing steel prior to repair (I
13、CRI No. 310.1R).3a location most distant from the crit-ical design locations for maximum moments or maximum shear. In this case, evaluate the remaining area of reinforcement by calculating moment and shear at the affected sections.(c) ACI code provisionsProvi-sions of Chapter 20 of ACI 318-11 may be
14、 used to modify the strength-reduction factor when the actual dimensions and material proper-ties have been determined through measurements and testing. Moment redistribution provisions (ACI 318-11, Section 8.4) may be used to consider inelastic effects that may reduce the required capacity at the s
15、ection under consideration.Where a loss of 10 percent or more has been identified, check the orig-inal design to determine if the remaining reinforcement is adequate. Also, confirm the absence of design errors and that structure use remains the same.If additional or replacement reinforcement is requ
16、ired, a new reinforcing bar may be lap spliced to the existing bar(s). Lap length is determined in accordance with ACI 318. Additional concrete removal may be necessary to properly splice the new steel reinforcing bar. Mechanical or welded splices that follow code provisions could also be used. Weld
17、ing should conform to ANSI/AWS D1.4. Verify the structures ability to carry construction loads during bar replacement or reinforcement. If mechanical splices are used, it may be necessary to shore the section before cutting the reinforcement to install a mechanical splice.After placing the new reinf
18、orcement, place the repair material where concrete was removed. The repair material should be compatible dimensionally; permeability-wise; chemically; electrochemically; and, if required, aesthetically with the existing concrete.If additional reinforcement is required, fiber-reinforced polymer (FRP)
19、 bars and strips may be considered as an alter-native to placement of new steel reinforcing bars. ACI 440R discusses the use of FRP reinforcement. If FRP is used, fire code issues, softening of epoxy adhesive at 120 to 140F (49 to 60C), ductility, and other parameters should be carefully evaluated.A
20、lthough concrete normally provides reinforcement with excellent corrosion protection, corrosion is possible. For example, when the concrete fails to resist the ingress of corrosion-causing substances, if the structure was improperly designed for the service environment, where the environment was not
21、 as anticipated, or changes occurred during the service life of the structure. Mixture characteristics of the concrete, proper placement and curing, thickness of concrete cover over the reinforcing steel, crack-control measures, and implementation of measures designed specifically for corrosion prot
22、ection are factors that help control the onset and rate of corrosion. Refer to ACI 222R for further discus-sion on the causes and prevention of reinforcement corrosion in concrete.SummaryThe loss of reinforcement section at less than 10 percent is generally accepted, provided the engineer is satisfi
23、ed that the original design is adequate and no changes of use or demand issues have occurred (for example, changes in applied loads or environmental exposure). Understand the corrosion cause (for example, chloride exposure), to determine if the corrosion activity has slowed or stopped and to establi
24、sh a timeframe for the corrosion deterioration process (ICRI No. 310.1R; ACI 364.6T). Generally, however, this answer cannot be applied to prestressing reinforcement.ReferencesCommittee documents are listed first by document number and year of publication followed by authored documents listed alphab
25、etically.American Concrete InstituteACI 222R-01Protection of Metals in Concrete against Corrosion (Reapproved 2010) ACI 318-11Building Code Requirements for Structural Concrete and Commentary ACI 364.6T-02Tech-Note: Concrete Removal in Repairs Involving Corroded Reinforcing Steel (Reapproved 2011) A
26、CI 440R-07Report on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures Fig. 3Repair of reinforcing steel due to loss of section where the loss of section is greater than 10 percent (ICRI No. 310.1R).4American Welding SocietyANSI/AWS D1.4-11Structural Welding CodeReinforced SteelInt
27、ernational Concrete Repair InstituteNo. 310.1R-2008Guide for Surface Preparation for the Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion (formerly No. 03730)Reported by Committee 364ACI TechNotes are intended for reference for the design and construction of concrete struct
28、ures. This document is intended for the use of indi-viduals who are competent to evaluate the significance and limitations of its content and who will accept responsibility for the application of the information it contains. The American Concrete Institute disclaims any and all responsibility for th
29、e accuracy of the content and shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents.ACI 364.10T-14 was adopted and published July 2014.Copyright 2014, American Concrete Institute.All rights reserved including the rights of re
30、production and use in any form or by any means, including the 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
31、 is obtained from the copyright proprietors.For additional copies, please contact: American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 Phone: 248-848-3700, Fax: 348-848-3701, www.concrete.orgFred R. Goodwin, Chair James H. Loper, SecretaryRandal M. Beard Charles J. Hook
32、ham David A. VanOckerBenoit Bissonnette Lawrence F. Kahn Alexander M. VaysburdChristopher D. Brown Ashok M. Kakade Kurt F. von FayDouglas Burke Dov Kaminetzky James WarnerRyan Alexander Carris James M. Kasper Patrick M. WatsonBruce A. Collins Keith E. Kesner David W. WhitmoreBrian Lee Cope Erick N.
33、LarsonBoris Dragunsky Marjorie M. Lynch Consulting MembersPeter Emmons Pritpal S. Mangat Robert V. GeveckerPaul E. Gaudette Surendra K. Manjrekar Stephen A. JohansonTimothy R. W. Gillespie James E. McDonald Emroy L. KempZareh B. Gregorian William R. Nash Howard H. Newlon, Jr.Pawan R. Gupta Jay H. Paul Weilan SongJohn L. Hausfeld K. Nam Shiu Dela TharmabalaRon Heffron Thomas E. Spencer Robert TracyRobert L. Henry John A. Tanner William F. WescottKal R. Hindo Valery Tokar
