224.1R-07 Causes, Evaluation, and Repair of Cracks in ...

1 ACI , Evaluation, and Repairof Cracks in Concrete StructuresReported by ACI Committee 224 American Concrete Institute Advancing concrete knowledgeCauses, Evaluation, and Repair of Cracksin Concrete StructuresFirst PrintingMarch 2007 ISBN 978-0-87031-234-2 Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This materialmay not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or otherdistribution and storage media, without the written consent of technical committees responsible for ACI committee reports and standards strive to avoid ambiguities,omissions, and errors in these documents. In spite of these efforts, the users of ACI documents occa-sionally find information or requirements that may be subject to more than one interpretation or may beincomplete or incorrect. Users who have suggestions for the improvement of ACI documents arerequested to contact committee documents are intended for the use of individuals who are competent to evaluate thesignificance and limitations of its content and recommendations and who will accept responsibility for theapplication of the material it contains.

2 Individuals who use this publication in any way assume all risk andaccept total responsibility for the application and use of this information in this publication is provided as is without warranty of any kind, either express or implied,including but not limited to, the implied warranties of merchantability, fitness for a particular purpose and its members disclaim liability for damages of any kind, including any special, indirect, incidental,or consequential damages, including without limitation, lost revenues or lost profits, which may resultfrom the use of this is the responsibility of the user of this document to establish health and safety practices appropriate tothe specific circumstances involved with its use. ACI does not make any representations with regard tohealth and safety issues and the use of this document. The user must determine the applicability of allregulatory limitations before applying the document and must comply with all applicable laws and regula-tions, including but not limited to, United States Occupational Safety and Health Administration (OSHA)health and safety information: ACI documents are available in print, by download, on CD-ROM, through electronicsubscription, or reprint and may be obtained by contacting ACI standards and committee reports are gathered together in the annually revised ACI Manual ofConcrete Practice (MCP).

3 American Concrete Institute38800 Country Club DriveFarmington Hills, MI :248-848-3700 supersedes ACI and was adopted and published inMarch 2007, American Concrete 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, printed, written, or oral, or recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors. Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning,designing, executing, and inspecting construction. Thisdocument is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it American Concrete Institute disclaims any and allresponsibility for the stated principles.

4 The Institute shall notbe liable for any loss or damage arising 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 restated in mandatory language for incorporation bythe , Evaluation, and Repair of Cracksin Concrete StructuresReported by ACI Committee 224 ACI 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 their proper : 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; plastic; polymer;precast concrete; prestressed concrete; reinforced concrete; Repair ; resins;settlement shrinkage; shrinkage; slab-on-ground; specification; thermalexpansion; volume , p.

5 1 Causes and control of cracking,p. Cracking of plastic Cracking of hardened concreteChapter 2 Evaluation of cracking, p. Determination of location and extent of Selection of Repair proceduresChapter 3 Methods of crack Repair , p. Epoxy Routing and Near-surface reinforcing and Additional Drilling and Gravity Crack Polymer Overlay and surface Autogenous healingChapter 4 References, p. Referenced standards and Cited referencesMohamed N. Abou-ZeidFouad H. FouadRalf LeistikowRandall W. PostonJames P. Barlow*David W. FowlerPeter A. LipphardtRoyce J. RhoadsFlorian G. BarthGrant T. HalvorsenEdward G. NawyJohn W. RobertsJ. Floyd BestWill HansenKamran M. NematiAndrew ScanlonDavid Darwin Harvey H. Haynes*Keith A. PashinaAndrea J. SchokkerJohn F. Duntemann*Member of task group that prepared these revisions. Chair of task group that prepared these J. Frosch*ChairJeffrey S. COMMITTEE REPORTPREFACEC racks in concrete have many causes.

6 They may affectappearance only, or 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 acceptable for buildings may not be accept-able in water-retaining 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 addressthe causes of the Cracks as well as the Cracks report is intended to serve as a tool in the process ofcrack evaluation and Repair of concrete causes of Cracks in concrete are summarized alongwith the principal procedures used for crack control. Bothplastic and hardened concrete are considered. The impor-tance of design, detailing, construction procedures, concreteproportioning, and material properties are techniques and methodology for crack evaluation aredescribed.

7 The need to determine the causes of cracking as anecessary prerequisite to Repair 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 methods of crack Repair are presented, includingthe techniques, advantages and disadvantages, and areas ofapplication for 1 CAUSES AND CONTROLOF IntroductionThis chapter presents a brief summary of the causes ofcracks and means for their control. Cracks are categorized asoccurring either in plastic concrete or hardened concrete(Kelly 1981; Price 1982). In addition to the informationprovided herein, further details are presented in ACI 224 Rand articles by Carlson et al. (1979), Kelly (1981), Price(1982), and Abdun-Nur (1983). Additional references arecited throughout the Cracking of plastic Plastic shrinkage cracking When moisture evapo-rates from the surface of freshly placed concrete faster thanit is replaced by bleed water, the surface concrete to the restraint provided by the concrete below thedrying surface layer, tensile stresses develop in the weak,stiffening plastic concrete.

8 This results in shallow Cracks ofvarying depths that may form a random, polygonal pattern,or be essentially parallel to one another (Fig. ). 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 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 shrinkage cracking is usually associated with therapid loss of moisture caused by a combination of factorsthat include 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 concrete with a greater tendency to 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 can be taken to prevent rapid moisture loss due tohot weather and dry winds (ACI 224R, , and 305R).

9 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 reduce 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 Settlement cracking 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 the restraining element(Fig. ). When associated with reinforcing steel, settlementcracking increases with increasing bar size, increasingslump, and decreasing cover (Dakhil et al.)

10 1975); this isshown in Fig. for a limited range of these variables. Thedegree of settlement cracking may be intensified by insufficientvibration or by the use of leaking or highly flexible and Malisch (1999) demonstrated that the additionof fibers can reduce the formation of settlement following items will reduce settlement cracking: Form design following ACI 347; Concrete vibration (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 );Fig. Typical plastic shrinkage cracking (Price 1982).CAUSES, EVALUATION, AND Repair OF Use of the lowest possible slump; An increase in concrete cover; and Addition of Cracking of hardened Drying shrinkage A 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 much as 1%.