ASTM C512 C512M-2010 Standard Test Method for Creep of Concrete in Compression《受压中混凝土蠕变的标准试验方法》.pdf

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1、Designation: C512/C512M 10Standard Test Method forCreep of Concrete in Compression1This standard is issued under the fixed designation C512/C512M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revision. A number

2、in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the creepof molded concrete cylinders subjected to sustained longitudi-nal compressive load. This

3、 test method is limited to concrete inwhich the maximum aggregate size does not exceed 50 mm 2in.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used in

4、dependently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet

5、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C39/C39M Test Method for Compressive Strength of Cy-lindrical Concrete SpecimensC192/C192M Practice for Making and Curing ConcreteTest Specimens in the Laboratory

6、C470/C470M Specification for Molds for Forming Con-crete Test Cylinders VerticallyC617 Practice for Capping Cylindrical Concrete SpecimensC670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction Materials3. Significance and Use3.1 This test method measures the load-

7、induced time-dependent compressive strain at selected ages for concreteunder an arbitrary set of controlled environmental conditions.3.2 This test method can be used to compare creep poten-tials of different concretes. A procedure is available, using thedeveloped equation (or graphical plot), for ca

8、lculating stressfrom strain data within massive non-reinforced concrete struc-tures. For most specific design applications, the test conditionsset forth herein must be modified to more closely simulate theanticipated curing, thermal, exposure, and loading age condi-tions for the prototype structure.

9、 Current theories and effects ofmaterial and environmental parameters are presented in ACISP-9, Symposium on Creep of Concrete.33.3 In the absence of a satisfactory hypothesis governingcreep phenomena, a number of assumptions have been devel-oped that have been generally substantiated by test andexp

10、erience.3.3.1 Creep is proportional to stress from 0 to 40 % ofconcrete compressive strength.3.3.2 Creep has been conclusively shown to be directlyproportional to paste content throughout the range of pastecontents normally used in concrete. Thus, the creep character-istics of concrete mixtures cont

11、aining aggregate of maximumsize greater than 50 mm 2 in. may be determined from thecreep characteristics of the minus 50-mm minus 2-in. fractionobtained by wet-sieving. Multiply the value of the character-istic by the ratio of the cement paste content (proportion byvolume) in the full concrete mixtu

12、re to the paste content of thesieved sample.3.4 The use of the logarithmic expression (Section 8) doesnot imply that the creep strain-time relationship is necessarilyan exact logarithmic function; however, for the period of oneyear, the expression approximates normal creep behavior withsufficient ac

13、curacy to make possible the calculation of param-eters that are useful for the purpose of comparing concretes.3.5 There are no data that would support the extrapolationof the results of this test to tension or torsion.4. Apparatus4.1 MoldsMolds shall be cylindrical conforming to theprovisions of Pra

14、ctice C192/C192M, or to the provisions ofSpecification C470/C470M. If required, provisions shall bemade for attaching gauge studs and inserts, and for affixingintegral bearing plates to the ends of the specimen as it is cast.1This test method is under the jurisdiction of ASTM Committee C09 onConcret

15、e and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.61 on Testing for Strength.Current edition approved Dec. 1, 2010. Published January 2011. Originallyapproved in 1963. Last previous edition approved in 2002 as C51202. DOI:10.1520/C0512_C0512M-10.2For referenced ASTM stand

16、ards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Concrete Institute (ACI), P.O. Box 9094, FarmingtonHills, MI 4

17、8333-9094, http:/www.concrete.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 Horizontal molds shall conform to the requirements ofthe section on horizontal molds for creep test cylinders ofPractice C192/C192M. A horizontal

18、 mold that has provensatisfactory is shown in Fig. 1.4.2 Loading Frame, capable of applying and maintainingthe required load on the specimen, despite any change in thedimension of the specimen. In its simplest form the loadingframe consists of header plates bearing on the ends of theloaded specimens

19、, a load-maintaining element that is either aspring or a hydraulic capsule or ram, and threaded rods to takethe reaction of the loaded system. Bearing surfaces of theheader plates shall not depart from a plane by more than 0.025mm 0.001 in. In any loading frame, it is not prohibited tostack several

20、specimens for simultaneous loading. The lengthbetween header plates shall not exceed 1780 mm 70 in.When a hydraulic load-maintaining element is used, severalframes may be loaded simultaneously through a central hy-draulic pressure-regulating unit consisting of an accumulator, aregulator, indicating

21、gages, and a source of high pressure, suchas a cylinder of nitrogen or a high-pressure pump. Springs suchas railroad car springs may be used to maintain the load inframes similar to those described above; the initial compres-sion shall be applied by means of a portable jack or testingmachine. When s

22、prings are used, care should be taken toprovide a spherical head or ball joint, and end plates rigidenough to ensure uniform loading of the cylinders. Fig. 2shows an acceptable spring-loaded frame. Means shall beprovided for measuring the load to the nearest 2 % of totalapplied load. It is not prohi

23、bited to use a permanently installedhydraulic pressure gauge or a hydraulic jack and a load cellinserted in the frame when the load is applied or adjusted.4.3 Strain-Measuring DeviceSuitable apparatus shall beprovided for the measurement of longitudinal strain in thespecimen to the nearest 10 millio

24、nths. It is not prohibited forthe apparatus to be embedded, attached, or portable. If aportable apparatus is used, gauge points shall be attached to thespecimen in a positive manner. Attached gages relying onfriction contact are not permissible. If an embedded device isused, it shall be situated so

25、that its strain movement occursalong the longitudinal axis of the cylinder. If external devicesare used, strains shall be measured on not less than two gaugelines spaced uniformly around the periphery of the specimen.The gages may be instrumented so that the average strain on allgauge lines can be r

26、ead directly. The effective gauge lengthshall be at least three times the maximum size of aggregate inthe concrete. The strain-measuring device shall be capable ofmeasuring strains for at least 1 year without change incalibration.NOTE 1Systems in which the varying strains are compared with aconstant

27、-length standard bar are considered most reliable, but unbondedelectrical strain gages are satisfactory.5. Test Specimens5.1 Specimen SizeThe diameter of each specimen shall be150 6 1.5 mm 6 6 0.6 in., and the length shall be at least 290mm 11.5 in. When the ends of the specimen are in contactwith s

28、teel bearing plates, the specimen length shall be at leastequal to the gauge length of the strain-measuring apparatusplus the diameter of the specimen. When the ends of thespecimen are in contact with other concrete specimens similarto the test specimen, the specimen length shall be at least equalto

29、 the gauge length of the strain-measuring apparatus plus 40mm 1.5 in. Between the test specimen and the steel bearingplate at each end of a stack, a supplementary noninstrumentedcylinder whose diameter is equal to that of the test cylindersand whose length is at least half its diameter shall be inst

30、alled.5.2 Fabricating SpecimensThe maximum size of aggre-gate shall not exceed 50 mm 2 in. (Section 3). Vertically castcylinders shall be fabricated in accordance with the provisionsof Practice C192/C192M. The ends of each cylinder shall meetthe planeness requirements described in the scope of Pract

31、iceC617 (Note 2). Horizontally cast specimens shall be consoli-dated by the method appropriate to the consistency of theconcrete as indicated in the methods of consolidation section ofPractice C192/C192M. Care must be taken to ensure that therod or vibrator does not strike the strain meter. When vib

32、rationis used, the concrete shall be placed in one layer and thevibrating element shall not exceed 35 mm 1.3 in. in diameter.When rodding is used, the concrete shall be placed in twoapproximately equal layers and each layer shall be rodded 25times evenly along each side of the strain meter. Aftercon

33、solidation, the concrete shall be struck off with trowel orfloat then trowelled the minimum amount to form the concretein the opening concentrically with the rest of the specimen. Itis not prohibited to use a template curved in the radius of thespecimen as a strikeoff to shape and finish the concret

34、e moreprecisely in the opening. When cylinders are to be stacked,lapping of ends is strongly recommended.NOTE 2Requirements for planeness may be met by capping, lapping,or, at the time of casting, fitting the ends with bearing plates normal to theaxis of the cylinder.5.3 Number of SpecimensNo fewer

35、than six specimens(Note 3) shall be made from a given batch of concrete for eachtest condition; two shall be tested for compressive strength,two shall be loaded and observed for total deformation, andtwo shall remain unloaded for use as controls to indicateFIG. 1 Horizontal Mold for Creep SpecimensC

36、512/C512M 102deformations due to causes other than load. Each strength andcontrol specimen shall undergo the same curing and storagetreatment as the loaded specimen.NOTE 3It is recommended that specimens be tested in triplicatealthough duplicate specimens are acceptable.6. Curing and Storage of Spec

37、imens6.1 Standard CuringBefore removal from the molds,specimens shall be stored at 23.0 6 2.0 C 73.5 6 3.5 F andcovered to prevent evaporation. The specimens shall be re-moved from the molds not less than 20 nor more than 48 h afterFIG. 2 Spring-Loaded Creep FrameC512/C512M 103molding and stored in

38、a moist condition at a temperature of23.0 6 2.0 C 73.5 6 3.5 F until the age of 7 days. A moistcondition is that in which free water is maintained on thesurfaces of the specimens at all times. Specimens shall not beexposed to a stream of running water nor be stored in water.After the completion of m

39、oist curing the specimens shall bestored at a temperature of 23.0 6 1.0 C 73.5 6 1.5 F andat a relative humidity of 50 6 4 % until completion of the test.6.2 Basic Creep CuringIf it is desired to prevent the gainor loss of water during the storage and test period, specimensshall at the time of fabri

40、cation or stripping be enclosed andsealed in moistureproof jackets (for example, copper or butylrubber) to prevent loss of moisture by evaporation and shallremain sealed throughout the period of storage and testing.6.3 Variable Curing Temperature RegimenWhen it isdesired to introduce the effect of t

41、emperature on the elastic andinelastic properties of a concrete (as, for example, the adiabatictemperature conditions existing in massive concrete or tem-perature conditions to which concrete is subjected duringaccelerated curing), temperatures within the specimen storagefacility shall be controlled

42、 to correspond to the desired tem-perature history. The user shall be responsible for establishingthe time-temperature history to be followed and the permissiblerange of deviation therefrom.6.4 Other Curing ConditionsOther test ages and ambientstorage conditions may be substituted when information i

43、srequired for specific applications. The storage conditions shallbe carefully detailed in the report.7. Procedure7.1 Age at LoadingWhen the purpose of the test is tocompare the creep potential of different concretes, initially loadthe specimens at an age of 28 days. When the complete creepbehavior o

44、f a given concrete is desired, prepare the specimensfor initial loading in the following ages: 2, 7, 28, and 90 days,and 1 year. If information is desired for other ages of loading,include the age in the report.7.2 Loading DetailsImmediately before loading the creepspecimens, determine the compressi

45、ve strength of the strengthspecimens in accordance with Test Method C39/C39M. At thetime unsealed creep specimens are placed in the loading frame,cover the ends of the control cylinders to prevent loss ofmoisture (Note 4). Load the specimens at an intensity of notmore than 40 % of the compressive st

46、rength at the age ofloading. Take strain readings immediately before and afterloading, 2 to 6 h later, then daily for 1 week, weekly until theend of 1 month, and monthly until the end of 1 year. Beforetaking each strain reading, measure the load. If the load variesmore than 2 % from the correct valu

47、e, it must be adjusted (Note5). Take strain readings on the control specimens on the sameschedule as the loaded specimens.NOTE 4In placing creep specimens in the frame, take care in aligningthe specimens to avoid eccentric loading. When cylinders are stacked andexternal gages are used, it may be hel

48、pful to apply a small preload suchthat the resultant stress does not exceed 1380 kPa 200 psi and note thestrain variation around each specimen, after which the load may beremoved and the specimens realigned for greater strain uniformity.NOTE 5Where springs are used to maintain the load, the adjustme

49、ntcan be accomplished by applying the correct load and tightening the nutson the threaded reaction rods.8. Calculation8.1 Calculate the total load-induced strain per unit stress atany time as the difference between the average strain values ofthe loaded and control specimens divided by the average stress.To determine creep strain per unit stress for any age, subtractfrom the total load-induced strain per unit stress at that age thestrain per unit stress immediately after loading. If desired, plottotal strain per unit stress on