1、Designation: C 512 02Standard Test Method forCreep of Concrete in Compression1This standard is issued under the fixed designation C 512; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parenth
2、eses indicates the year of last reapproval. Asuperscript epsilon (e) 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 test met
3、hod is limited to concrete inwhich the maximum aggregate size does not exceed 2 in. (50mm).1.2 The values stated in inch-pound units are to be regardedas 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
4、the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:C 39/C 39M Test Method for Compressive Strength of Cy-lindrical Concrete Specimens2C 192/C 192M Practice f
5、or Making and Curing ConcreteTest Specimens in the Laboratory2C 470/C 470M Specification for Molds for Forming Con-crete Test Cylinders Vertically2C 617 Practice for Capping Cylindrical Concrete Speci-mens2C 670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction Ma
6、terials23. Significance and Use3.1 This test method measures the load-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
7、 is available, using thedeveloped equation (or graphical plot), for calculating 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, therm
8、al, exposure, and loading age condi-tions for the prototype structure. 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
9、 been devel-oped that have been generally substantiated by test andexperience.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 i
10、n concrete. Thus, the creep character-istics of concrete mixtures containing aggregate of maximumsize greater than 2 in. (50 mm) may be determined from thecreep characteristics of the minus 2-in. (minus 50-mm) fractionobtained by wet-sieving. Multiply the value of the character-istic by the ratio of
11、 the cement paste content (proportion byvolume) in the full concrete mixture 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 on
12、eyear, the expression approximates normal creep behavior withsufficient accuracy 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. Appar
13、atus4.1 MoldsMolds shall be cylindrical conforming to theprovisions of Practice C 192/C 192M, or to the provisions ofSpecification C 470/C 470M. If required, provisions shall bemade for attaching gage studs and inserts, and for affixingintegral bearing plates to the ends of the specimen as it is cas
14、t.4.1.1 Horizontal molds shall conform to the requirements ofthe section on horizontal molds for creep test cylinders ofPractice C 192/C 192M. A horizontal mold that has provensatisfactory is shown in Fig. 1.4.2 Loading Frame, capable of applying and maintainingthe required load on the specimen, des
15、pite any change in thedimension of the specimen. In its simplest form the loading1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.61 on Testing for Strength.Current edition approved Aug. 10, 2002.
16、 Published October 2002. Originallypublished as C 512 63 T. Last previous edition C 512 87 (1994).2Annual Book of ASTM Standards, Vol 04.02.3Available from the American Concrete Institute, P. O. Box 19150, Detroit, MI48219.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh
17、ohocken, PA 19428-2959, United States.frame consists of header plates bearing on the ends of theloaded specimens, 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 no
18、t depart from a plane by more than 0.001in. (0.025 mm). In any loading frame, it is not prohibited tostack several specimens for simultaneous loading. The lengthbetween header plates shall not exceed 70 in. (1780 mm).When a hydraulic load-maintaining element is used, severalframes may be loaded simu
19、ltaneously through a central hy-draulic pressure-regulating unit consisting of an accumulator, aregulator, indicating 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
20、those described above; the initial compres-sion shall be applied by means of a portable jack or testingmachine. When springs 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 sprin
21、g-loaded frame. Means shall beprovided for measuring the load to the nearest 2 % of totalapplied load. It is not prohibited to use a permanently installedhydraulic pressure gage or a hydraulic jack and a load cellinserted in the frame when the load is applied or adjusted.4.3 Strain-Measuring DeviceS
22、uitable apparatus shall beprovided for the measurement of longitudinal strain in thespecimen to the nearest 10 millionths. It is not prohibited forthe apparatus to be embedded, attached, or portable. If aportable apparatus is used, gage points shall be attached to thespecimen in a positive manner. A
23、ttached gages relying onfriction contact are not permissible. If an embedded device isused, it shall be situated so that its strain movement occursalong the longitudinal axis of the cylinder. If external devicesare used, strains shall be measured on not less than two gagelines spaced uniformly aroun
24、d the periphery of the specimen.The gages may be instrumented so that the average strain on allgage lines can be read directly. The effective gage length shallbe at least three times the maximum size of aggregate in theconcrete. The strain-measuring device shall be capable ofmeasuring strains for at
25、 least 1 year without change incalibration.NOTE 1Systems in which the varying strains are compared with aconstant-length standard bar are considered most reliable, but unbondedelectrical strain gages are satisfactory.5. Test Specimens5.1 Specimen SizeThe diameter of each specimen shall be6 6116 in.
26、(or 150 6 1.6 mm), and the length shall be at least1112 in. (292 mm). When the ends of the specimen are incontact with steel bearing plates, the specimen length shall beat least equal to the gage length of the strain-measuringapparatus plus the diameter of the specimen. When the ends ofthe specimen
27、are in contact with other concrete specimenssimilar to the test specimen, the specimen length shall be atleast equal to the gage length of the strain-measuring apparatusplus 112 in. (38 mm). Between the test specimen and the steelbearing plate at each end of a stack, a supplementary nonin-strumented
28、 cylinder whose diameter is equal to that of the testcylinders and whose length is at least half its diameter shall beinstalled.5.2 Fabricating SpecimensThe maximum size of aggre-gate shall not exceed 2 in. (50-mm) (Section 3). Vertically castcylinders shall be fabricated in accordance with the prov
29、isionsof Practice C 192/C 192M. The ends of each cylinder shallmeet the planeness requirements described in the scope ofPractice C 617 (Note 2). Horizontally cast specimens shall beconsolidated by the method appropriate to the consistency ofthe concrete as indicated in the methods of consolidationse
30、ction of Practice C 192/C 192M. Care must be taken toensure that the rod or vibrator does not strike the strain meter.When vibration is used, the concrete shall be placed in onelayer and the vibrating element shall not exceed 114 in. (32mm) in diameter. When rodding is used, the concrete shall bepla
31、ced in two approximately equal layers and each layer shallbe rodded 25 times evenly along each side of the strain meter.After consolidation, the concrete shall be struck off with trowelor float, then trowelled the minimum amount to form theconcrete in the opening concentrically with the rest of thes
32、pecimen. It is not prohibited to use a template curved in theradius of the specimen as a strikeoff to shape and finish theFIG. 1 Horizontal Mold for Creep SpecimensFIG. 2 Spring-Loaded Creep FrameC512022concrete more precisely in the opening. When cylinders are tobe stacked, lapping of ends is stron
33、gly 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 than six specimens(Note 3) shall be made from a given batch of concrete for eachtest cond
34、ition; 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 indicatedeformations due to causes other than load. Each strength andcontrol specimen shall undergo the same curing and storagetreatment as
35、the loaded specimen.NOTE 3It is recommended that specimens be tested in triplicatealthough duplicate specimens are acceptable.6. Curing and Storage of Specimens6.1 Standard CuringBefore removal from the molds,specimens shall be stored at 73.4 6 3.0F (23.0 6 1.7C) andcovered to prevent evaporation. T
36、he specimens shall be re-moved from the molds not less than 20 nor more than 48 h aftermolding and stored in a moist condition at a temperature of73.4 6 3.0F until the age of 7 days. A moist condition is thatin which free water is maintained on the surfaces of thespecimens at all times. Specimens sh
37、all not be exposed to astream of running water nor be stored in water. After thecompletion of moist curing the specimens shall be stored at atemperature of 73.4 6 2.0F (23.0 6 1.1C) and at a relativehumidity of 50 6 4 % until completion of the test.6.2 Basic Creep CuringIf it is desired to prevent t
38、he gainor loss of water during the storage and test period, specimensshall at the time of fabrication 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 an
39、d testing.6.3 Variable Curing Temperature RegimenWhen it isdesired to introduce the effect of temperature 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
40、duringaccelerated curing), temperatures within the specimen storagefacility shall be controlled 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 Curin
41、g ConditionsOther test ages and ambientstorage conditions may be substituted when information isrequired 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
42、 concretes, initially loadthe specimens at an age of 28 days. When the complete creepbehavior of 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 r
43、eport.7.2 Loading DetailsImmediately before loading the creepspecimens, determine the compressive strength of the strengthspecimens in accordance with Test Method C 39/C 39M. At thetime unsealed creep specimens are placed in the loading frame,cover the ends of the control cylinders to prevent loss o
44、fmoisture (Note 4). Load the specimens at an intensity of notmore than 40 % of the compressive strength 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. Beforeta
45、king each strain reading, measure the load. If the load variesmore than 2 % from the correct value, 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
46、 to avoid eccentric loading. When cylinders are stacked andexternal gages are used, it may be helpful to apply a small preload suchthat the resultant stress does not exceed 200 psi (1380 kPa) and note thestrain variation around each specimen, after which the load may beremoved and the specimens real
47、igned for greater strain uniformity.NOTE 5Where springs are used to maintain the load, the adjustmentcan 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 pound persquare inch (or kilopascal
48、) at any time as the differencebetween the average strain values of the loaded and controlspecimens divided by the average stress. To determine creepstrain per pound-force per square inch (or kilopascal) for anyage, subtract from the total load-induced strain per pound-forceper square inch (or kilop
49、ascal) at that age the strain perpound-force per square inch (or kilopascal) immediately afterloading. If desired, plot total strain per pound-force per squareinch (or kilopascal) on semilog coordinate paper, on which thelogarithmic axis represents time, to determine the constants 1/Eand F (K) for the following equation:e51/E! 1 FK!ln t 1 1! (1)where:e = total strain psi (or kPa),E = instantaneous elastic modulus, psi (or kPa),F(K) = creep rate, calculated as the slope of a straight linerepresenting the creep curve on the semilog plot,andt = time after load
