ACI 209 1R-2005 Report on Factors Affecting Shrinkage and Creep of Hardened Concrete《硬化混凝土收缩和徐变影响因素的报告》.pdf

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1、ACI 209.1R-05 became effective July 25, 2005.Copyright 2005, American Concrete Institute.All 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 r

2、ecording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning,designing, executing, an

3、d 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 contains.The American Concrete Institute disclaims a

4、ny and allresponsibility for the stated principles. The Institute shall notbe 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

5、, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.209.1R-1Report on Factors Affecting Shrinkage and Creepof Hardened ConcreteReported by ACI Committee 209ACI 209.1R-05This guide describes the effects of numerous variables on shrinkage andcreep of hardened concr

6、ete, including mixture proportions, environment,design, and construction. This document is aimed at designers who wish togain further information about factors changing shrinkage and creep butdoes not include information on the prediction of shrinkage and creep orstructural design issues associated

7、with shrinkage and creep.Keywords: creep; drying shrinkage; strain.CONTENTSChapter 1Introduction, p. 209.1R-11.1Scope1.2Terminology and range of values of strains1.3Mechanisms of shrinkage and creep1.4Areas of recommended research1.5Additional sourcesChapter 2Factors affecting drying shrinkage,p. 20

8、9.1R-52.1Introduction2.2Effect of mixture proportions on drying shrinkage2.3Effect of environment on drying shrinkage2.4Effect of design and construction on dryingshrinkageChapter 3Factors affecting creep, p. 209.1R-83.1Introduction3.2Effect of mixture proportions on creep3.3Effect of environment on

9、 creep3.4Effect of construction and structural design on creepChapter 4References, p. 209.1R-114.1Referenced standards and reports4.2Cited references and reportsCHAPTER 1INTRODUCTION1.1ScopeFactors affecting shrinkage and creep of hardened concreteare presented to enable those involved in the evalua

10、tion andformulation of concrete mixtures to determine the effects ofthese factors. Section 1.2 of Chapter 1 defines terms used bythose evaluating shrinkage and creep, while Chapters 2 and 3describe effects of various factors on shrinkage and creep.This document does not include information on the pr

11、edictionof shrinkage and creep or structural design issues associatedwith shrinkage and creep.Akthem A. Al-Manaseer*Mario A. Chiorino Mohsen A. Issa Klaus A. RiederZdenek P. Bazant Marwan A. Daye Hesham Marzouk Ian RobertsonJeffrey J. Brooks Walter H. Dilger Baquan Miao Kenji SakataRonald G. Burg*N.

12、 John Gardner*Harald S. Mueller Nam K. ShiuDomingo J. Carreira Will Hansen Lawrence C. Novak Carlos Videla*Members of subcommittee that prepared this report.David B. McDonald*ChairW. Jason WeissSecretary209.1R-2 ACI COMMITTEE REPORTThis document is not intended as a primary referencesource for those

13、 studying shrinkage and creep; rather, it isaimed at designers who wish to gain further understanding ofthe effects of materials being used. This document alsoprovides references that provide direction for those wishingto seek additional information about shrinkage and creep.1.2Terminology and range

14、 of values of strainsTo discuss shrinkage and creep, it is important to definethe following terms:Total strain;Shrinkage;Autogenous shrinkage;Drying shrinkage;Carbonation shrinkage;Swelling;Load-induced strain;Initial strain at loading or nominal elastic strain;Crep strain;Basic creep;Drying creep;C

15、ompliance;Specific creep; andCreep coefficient.Various terms are shown in Fig. 1.1 and are described indetail below, together with an indication of typical valueranges. The values of total strain, shrinkage, and creep aretime-dependent. A thorough discussion of definitions, basicassumptions, and sta

16、ndard test methods for creep andshrinkage can be found in the references (RILEM TC 107-CSP 1998; Carreira and Burg 2000).Shrinkage and creep may occur in three dimensions;however, most research suggests that total strain, shrinkage,and creep occur in each dimension independently. Thus,changes in len

17、gth will be consistently used throughout thisdocument, rather than changes in volume.1.2.1 Total strainTotal strain is the total change inlength per unit length measured on a concrete specimensubjected to a sustained constant load at uniform tempera-ture. As shown in Fig. 1.1, total strain is the su

18、m of shrinkageand load-induced strain.1.2.2 ShrinkageShrinkage is the strain measured on aload-free concrete specimen.Shrinkage does not include changes in length due totemperature variations, but depends on the environment andon the configuration and size of the specimen. Shrinkagestrain is usually

19、 measured by casting companion load-freespecimens identical to the loaded concrete specimens used tomeasure the total strain. These companion specimens are castfrom the same concrete batch, have the same dimensions,and are stored in the same environment as the loadedconcrete specimens.Shrinkage valu

20、es are given as dimensionless strains(length change over a given length) expressed as percent,mm/mm, or in./in. It is common to describe shrinkage inmicrostrain or millionths, as the value of strain 106. Thus,1000 microstrain is equivalent to 1 103mm/mm.Values of long-term concrete shrinkage are typ

21、icallybetween 200 and 800 106mm/mm, (200 to 800 microstrain)(Zia, Ahmad, and Leming 1997) and mortar shrinkage typicallybetween 800 and 2000 106mm/mm (800 and 2000microstrain) (Heath and Roesler 1999). Cement pasteFig. 1.1Relationship between various measured and derived strain values. The figuresho

22、ws that the concrete undergoes autogenous shrinkage before drying. Once dryingcommences at time t0, drying shrinkage occurs. Upon loading, both drying and basiccreep occurs in the drying specimen.FACTORS AFFECTING SHRINKAGE AND CREEP OF HARDENED CONCRETE 209.1R-3shrinkage values are typically betwee

23、n 2000 and 6000 106mm/mm (2000 and 6000 microstrain) (Feldman 1969).1.2.3 Autogenous shrinkageThe shrinkage occurring inthe absence of moisture exchange (as in a sealed concretespecimen) due to the hydration reactions taking place insidethe cement matrix is termed autogenous shrinkage. Lesscommonly,

24、 it is termed “basic shrinkage” or “chemicalshrinkage.” Autogenous shrinkage was almost never consid-ered as a factor in research on shrinkage and creep before1990, and it has become a greater factor with the increaseduse of high-performance concrete. Factors affecting, and theprediction of autogeno

25、us shrinkage, are outside the scope ofthis report. As development of research continues in this area,ACI Committee 209 will present additional information.Autogenous shrinkage is usually small for many normalcompressive strength concretes and can usually be neglected.For concrete with water-cement r

26、atios (w/c) less than 0.40,however, autogenous shrinkage may be a significant compo-nent of the total measured shrinkage (Tazawa 1999).1.2.4 Drying shrinkageShrinkage occurring in a specimenthat is exposed to the environment and allowed to dry is calleddrying shrinkage. For normal-strength concrete,

27、 it is usuallyassumed that the entire shrinkage strain is from dryingshrinkage, and any contribution from autogenous shrinkage isneglected. Because drying shrinkage involves moisturemovement through the material and moisture loss, dryingshrinkage depends on the size and shape of the specimen.Due to

28、the relationship of drying shrinkage to water loss,it may be expected to reach a final value; although, this isdifficult to be confirmed experimentally due to the longduration of the drying process in normal size specimens(RILEM TC 107 1995; Al-Manaseer, Espion, and Ulm 1999;Bazant 1999). A final va

29、lue has been documented for spec-imens of hardened cement paste thin enough to dry to anequilibrium water content (Wittman et al. 1987).1.2.5 Carbonation shrinkageCarbonation shrinkage iscaused by the reaction of the calcium hydroxide within thecement matrix with carbon dioxide in the atmosphere.Fac

30、tors affecting, and the prediction of carbonationshrinkage, are outside the scope of this report.1.2.6 Plastic shrinkagePlastic shrinkage is defined byACI 116R as the shrinkage that takes place before cementpaste, mortar, grout, or concrete sets. Plastic shrinkage isoutside the scope of this report.

31、1.2.7 SwellingWhen concrete is placed in water it swells,which has been attributed to reduced capillary forces withinthe concrete (Kovler 1996). Few research studies have closelyrecorded the magnitude of swelling and studied the factorsaffecting the magnitude of this phenomenon. The expansionstrain

32、due to swelling is approximately 100 106mm/mm(100 microstrain) (McDonald 1990).1.2.8 Load-induced strainLoad-induced strain is thetime-dependent strain due to a constant sustained loadapplied at the age t. Experimentally, it is obtained bysubtracting from the total strain the shrinkage strainmeasure

33、d on load-free companion specimens with the samesize and shape as the loaded specimens and placed in thesame environment. The load-induced strain is frequentlysubdivided into an initial strain and a creep strain. The initialand creep strain components should be defined consistentlyso that their sum

34、corresponds to the appropriate load-inducedstrain (CEB 1993; RILEM TC 107 1995; Bazant and Baweja2000; Carreira and Burg 2000).1.2.9 Initial strain at loading or nominal elastic strainThe short-term strain at the moment of loading is termedinitial strain and is frequently considered as a nominal ela

35、sticstrain as it contains creep that occurs during the time taken tomeasure the strain. It is dependent on the duration of the loadapplication and strain reading procedures. The separation ofthis initial component of the load-induced strain is made forconvenience, and it may be determined using stan

36、dardizedprocedures for the experimental determination of a staticelastic modulus (corresponding to the strain in a shortinterval after load application) (CEB 1993; RILEM TC 107-CSP 1998; Bazant and Baweja 2000; Carreira and Burg2000). ASTM C 469 is often used to determine this value. Inthis test, th

37、e initial strain corresponds to a load duration of0.01 day (approximately 15 min) (Carreira and Burg 2000).Although often done by researchers, the committee recom-mends that the strain should not be separated into initial andcreep strains, due to the loading rate factors that affect theestimated ini

38、tial strain at loading.1.2.10 Creep strainCreep strain represents the time-dependent increase in strain under sustained constant loadtaking place after the initial strain at loading. It is obtainedfrom the load-induced strain by subtracting the initial straindefined in Section 1.2.9. The creep strai

39、n may be severaltimes greater than the initial strain. Creep strain may besubdivided into a drying and a nondrying component, termeddrying and basic creep, respectively.1.2.11 Basic creepBasic creep is the time-dependentincrease in strain under sustained constant load of a concretespecimen in which

40、moisture losses or gains are prevented(sealed specimen). It represents the creep at constant moisturecontent with no moisture movement through the material, and isconsequently independent of the specimen size and shape.To determine basic creep, it is necessary to measure the defor-mations of a set o

41、f sealed specimens under constant load and todetermine the total strain; and, if autogenous shrinkage cannotbe neglected, deformations of companion sealed, load-free spec-imens should be measured. It has not been determined whetherbasic creep approaches a final value, even after 30 years ofmeasureme

42、nt of sealed specimens (Bazant 1975; CEB 1993).1.2.12 Drying creepDrying creep is the additional creepoccurring in a specimen exposed to the environment andallowed to dry. As it is caused by the drying process, dryingcreep depends on the size and shape of the specimen and maybe expected to show a li

43、miting value at long term (RILEMTC 107 1995; Al-Manaseer, Espion, and Ulm 1999; Bazant1999; Bazant and Baweja 2000).Three sets of specimens are required to determine thedrying creep: a loaded set that is allowed to dry to determinethe total strain, a loaded set of sealed specimens to determinebasic

44、creep, and a load-free set at drying to determine thetotal shrinkage strain (Carreira and Burg 2000). This is math-ematically described in Eq. (1-1).209.1R-4 ACI COMMITTEE REPORTdrying creep = total strain of drying specimen (1-1) total strain of sealed specimen shrinkage of drying specimen1.2.13 Co

45、mplianceThe compliance J (t, t) describes thetime-dependent strain at age t caused by a unit uniaxialsustained load applied since loading age t. As a result of theprevious definitions, the compliance is given by Eq. (1-2).J(t,t) = (1-2)where t = age of the concrete, and t = age of the concrete atloa

46、ding.Values of compliance are given in units of 1/MPa or 1/psi.They range from 30 to 300 microstrain/MPa (0.20 to 2.00microstrain/psi) (Bazant and Baweja 2000).It is recommended that all the information for the predic-tion of the time-dependent-load-induced strains should beconveyed through the use

47、of compliance (CEB 1993;RILEM TC 107 1995; Bazant and Baweja 2000; Gardnerand Lockman 2001). Typical compliance for different valuesof age at loading t are presented in Fig. 1.2 using a loga-rithmic scale for time. 1.2.14 Specific creepSpecific creep is defined as the creepstrain per unit load and c

48、an be calculated as shown in Eq. (1-3).(1-3)The value of specific creep depends highly on the value ofthe initial strain estimated as part of the testing procedureand is not recommended by the committee.1.2.15 Creep coefficientThe creep coefficient is definedas the ratio of the creep strain to the initial strain or, identi-cally, as the ratio of the creep compliance to the compliancetotal strain drying-shrinkage strain autogenous shrinkage strainstress-specific creep = creep strainstress-total strain autogenous shrinkage drying shrinkage initial strainstress-