1、ACI 224.1R-07Causes, Evaluation, and Repairof Cracks in Concrete StructuresReported by ACI Committee 224American Concrete InstituteAdvancing concrete knowledgeCauses, Evaluation, and Repair of Cracksin Concrete StructuresFirst PrintingMarch 2007ISBN 978-0-87031-234-2Copyright by the American Concret
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10、00 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgACI 224.1R-07 supersedes ACI 224.1R-93 and was adopted and published inMarch 2007.Copyright 2007, American Concrete Institute.All rights reserved including rights of reproduction and use in any f
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14、nt 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 restated in mandatory language for incorporation bythe Architect/Engineer.Causes, Evaluation, and Repair of Cracksin Concrete Structure
15、sReported by ACI Committee 224ACI 224.1R-07The causes of cracks in concrete structures are summarized. The proce-dures used to evaluate cracking in concrete and the principal techniquesfor the repair of cracks are presented. The key methods of crack repair arediscussed, and guidance is provided for
16、their proper application.Keywords: alkali-silica reaction; alkali-carbonate reaction; autogenoushealing; concrete; consolidation; corrosion; cracking (fracturing); dryingshrinkage; epoxy resins; evaluation; grouting; heat of hydration; massconcrete; methacrylates; mixture proportion; overlay; plasti
17、c; polymer;precast concrete; prestressed concrete; reinforced concrete; repair; resins;settlement shrinkage; shrinkage; slab-on-ground; specification; thermalexpansion; volume change.CONTENTSPreface, p. 224.1R-2Chapter 1Causes and control of cracking,p. 224.1R-21.1Introduction1.2Cracking of plastic
18、concrete1.3Cracking of hardened concreteChapter 2Evaluation of cracking, p. 224.1R-92.1Introduction2.2Determination of location and extent of concretecracking2.3Selection of repair proceduresChapter 3Methods of crack repair, p. 224.1R-133.1Introduction3.2Epoxy injection3.3Routing and sealing3.4Near-
19、surface reinforcing and pinning3.5Additional reinforcement3.6Drilling and plugging3.7Gravity filling3.8Grouting3.9Drypacking3.10Crack arrest3.11Polymer impregnation3.12Overlay and surface treatments3.13Autogenous healingChapter 4References, p. 224.1R-184.1Referenced standards and reports4.2Cited ref
20、erencesMohamed N. Abou-Zeid Fouad H. Fouad Ralf Leistikow Randall W. PostonJames P. Barlow*David W. Fowler Peter A. Lipphardt Royce J. RhoadsFlorian G. Barth Grant T. Halvorsen Edward G. Nawy John W. RobertsJ. Floyd Best Will Hansen Kamran M. Nemati Andrew ScanlonDavid DarwinHarvey H. Haynes*Keith A
21、. Pashina Andrea J. SchokkerJohn F. Duntemann*Member of task group that prepared these revisions.Chair of task group that prepared these revisions.Robert J. Frosch*ChairJeffrey S. WestSecretary224.1R-2 ACI COMMITTEE REPORTPREFACECracks in concrete have many causes. They may affectappearance only, or
22、 they may indicate significant structuraldistress or a lack of durability. Cracks may represent the totalextent of the damage, or they may point to problems ofgreater magnitude. Their significance depends on the type ofstructure, as well as the nature of the cracking. For example,cracks that are acc
23、eptable for buildings may not be accept-able in water-retaining structures.Good crack repair techniques depend on knowing the causesand selecting appropriate repair procedures that take thesecauses into account; otherwise, the repair may only betemporary. Successful long-term repair procedures must
24、addressthe causes of the cracks as well as the cracks themselves.This report is intended to serve as a tool in the process ofcrack evaluation and repair of concrete structures.The causes of cracks in concrete are summarized alongwith the principal procedures used for crack control. Bothplastic and h
25、ardened concrete are considered. The impor-tance of design, detailing, construction procedures, concreteproportioning, and material properties are discussed.The techniques and methodology for crack evaluation aredescribed. The need to determine the causes of cracking as anecessary prerequisite to re
26、pair is emphasized. The selectionof successful repair techniques should consider the causes ofcracking, whether the cracks are active or dormant, and theneed for repair. Criteria for the selection of crack repairprocedures are based on the desired outcome.Twelve methods of crack repair are presented
27、, includingthe techniques, advantages and disadvantages, and areas ofapplication for each.CHAPTER 1CAUSES AND CONTROLOF CRACKING1.1IntroductionThis chapter presents a brief summary of the causes ofcracks and means for their control. Cracks are categorized asoccurring either in plastic concrete or ha
28、rdened concrete(Kelly 1981; Price 1982). In addition to the informationprovided herein, further details are presented in ACI 224Rand articles by Carlson et al. (1979), Kelly (1981), Price(1982), and Abdun-Nur (1983). Additional references arecited throughout the chapter.1.2Cracking of plastic concre
29、te1.2.1 Plastic shrinkage crackingWhen moisture evapo-rates from the surface of freshly placed concrete faster thanit is replaced by bleed water, the surface concrete shrinks.Due to the restraint provided by the concrete below thedrying surface layer, tensile stresses develop in the weak,stiffening
30、plastic concrete. This results in shallow cracks ofvarying depths that may form a random, polygonal pattern,or be essentially parallel to one another (Fig. 1.1). Thesecracks may be fairly wide (as much as 1/8 in. 3 mm) at thesurface. They range from a few inches to many feet in length,and are spaced
31、 from a few inches (millimeters) to as much as10 ft (3 m) apart. Plastic shrinkage cracks begin as shallowcracks, but can become full-depth cracks later in the life ofthe concrete.Plastic shrinkage cracking is usually associated with therapid loss of moisture caused by a combination of factorsthat i
32、nclude high air and concrete temperatures, low relativehumidity, and high wind velocity at the surface of theconcrete. Concrete with lower amounts of bleed water, suchas those containing mineral admixtures (especially silicafume) have a greater tendency to undergo plastic shrinkagecracking than conc
33、rete with a greater tendency to bleed.Because plastic shrinkage cracking is due to a differentialvolume change in the plastic concrete, successful controlmeasures require a reduction in the relative volume changebetween the surface and other portions of the concrete.Steps can be taken to prevent rap
34、id moisture loss due tohot weather and dry winds (ACI 224R, 302.1R, and 305R).These measures include the use of fog nozzles to saturate theair above the surface and the use of plastic sheeting to coverthe surface between finishing operations. Windbreaks toreduce the wind velocity and sunshades to re
35、duce the surfacetemperature are also helpful. It is good practice to scheduleflatwork after the windbreaks have been erected. During hot,windy weather with low humidity, it is sometimes advisableto reschedule the concrete placement or to initiate concreteoperations at night.1.2.2 Settlement cracking
36、Concrete has a tendency tocontinue to consolidate after initial placement, vibration, andfinishing. During this period, the plastic concrete may belocally restrained by reinforcing steel, a previous concreteplacement, or formwork. This local restraint may result invoids, cracks, or both, adjacent to
37、 the restraining element(Fig. 1.2). When associated with reinforcing steel, settlementcracking increases with increasing bar size, increasingslump, and decreasing cover (Dakhil et al. 1975); this isshown in Fig. 1.3 for a limited range of these variables. Thedegree of settlement cracking may be inte
38、nsified by insufficientvibration or by the use of leaking or highly flexible forms.Suprenant and Malisch (1999) demonstrated that the additionof fibers can reduce the formation of settlement cracks.The following items will reduce settlement cracking:Form design following ACI 347;Concrete vibration (
39、and revibration) (ACI 309R);Provision of a time interval between the placement ofconcrete in columns or deep beams and the placementof concrete in slabs and beams (ACI 309.2R);Fig. 1.1Typical plastic shrinkage cracking (Price 1982).CAUSES, EVALUATION, AND REPAIR OF CRACKS 224.1R-3Use of the lowest p
40、ossible slump; An increase in concrete cover; andAddition of fibers.1.3Cracking of hardened concrete1.3.1 Drying shrinkageA common cause of cracking inconcrete is restrained drying shrinkage. Drying shrinkage iscaused by the loss of moisture from the cement paste constit-uent, which can shrink by as
41、 much as 1%. Fortunately,aggregate particles provide internal restraint that reduces themagnitude of this volume change to about 0.06%. On theother hand, concrete tends to expand when wetted (thevolume increase can be the same order of magnitude as thatobserved due to shrinkage).These moisture-induc
42、ed volume changes are a characteristicof concrete. If the shrinkage of concrete could take placewithout restraint, the concrete would not crack. It is thecombination of shrinkage and restraint (provided by anotherpart of the structure, by the subgrade, or by the moist interiorof the concrete itself)
43、 that causes tensile stresses to develop.When the tensile strength of the material is exceeded, concretewill crack. Cracks may propagate at much lower stresses thanare required to cause crack initiation (ACI 446.1R).In massive concrete elements, tensile stresses are caused bydifferential shrinkage b
44、etween the surface and the interiorconcrete. The higher shrinkage at the surface causes cracks todevelop that may, with time, penetrate deeper into the concrete.The magnitude of the tensile stresses induced by volumechange is influenced by a combination of factors, includingthe amount and rate of sh
45、rinkage, the degree of restraint, themodulus of elasticity, and the amount of creep. The amountof drying shrinkage is influenced mainly by the amount andtype of aggregate and the cement paste (cement and water)content of the mixture. As the quantity of aggregateincreases, the shrinkage decreases (Pi
46、ckett 1956). The higherthe stiffness of the aggregate, the more effective it is inreducing the shrinkage of the concrete; that is, the shrinkageof concrete containing sandstone aggregate may be morethan twice that of concrete with granite, basalt, or high-quality limestone (Carlson 1938). The higher
47、 the water andcement contents, the greater the amount of drying shrinkage(U.S. Bureau of Reclamation 1975; Schmitt and Darwin1999; Darwin et al. 2004).Surface crazing (alligator pattern) on walls and slabs is anexample of drying shrinkage on a small scale. Crazingusually occurs when the surface laye
48、r of the concrete has ahigher water content than the interior concrete. The result isa series of shallow, closely spaced, fine cracks.A procedure that will help reduce settlement cracking, aswell as drying shrinkage in walls, is reducing the watercontent of the concrete as the wall is placed from th
49、e bottomto the top (U.S. Bureau of Reclamation 1975; ACI 304R).Using this procedure, bleed water from the lower portions ofthe wall will tend to equalize the water content within thewall. To be successful, this procedure needs careful controlof the concrete and proper consolidation.Shrinkage cracking can be controlled by using contractionjoints and proper detailing of the reinforcement. Shrinkagecracking may also be reduced or even eliminated by usingshrinkage-compensating cement or a shrinkage-compensatingadmixture. The reduction or elimination of subsl
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