1、Designation: C1768/C1768M 12 (Reapproved 2017)Standard Practice forAccelerated Curing of Concrete Cylinders1This standard is issued under the fixed designation C1768/C1768M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers two procedures for making andcuring cylindrical specimens of concrete under conditions thatinc
3、rease the rate of hydration at early ages. The procedures are:AWarm Water Method and BAutogenous Curing Method.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 sh
4、all be used independently 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 appr
5、o-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. (WarningFreshhydraulic cementitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.2)1.4 This international standard was developed in accor-dance
6、 with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Stand
7、ards:3C31/C31M Practice for Making and Curing Concrete TestSpecimens in the FieldC39/C39M Test Method for Compressive Strength of Cylin-drical Concrete SpecimensC125 Terminology Relating to Concrete and Concrete Ag-gregatesC143/C143M Test Method for Slump of Hydraulic-CementConcreteC172/C172M Practi
8、ce for Sampling Freshly Mixed Con-creteC173/C173M Test Method forAir Content of Freshly MixedConcrete by the Volumetric MethodC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryC231/C231M Test Method forAir Content of Freshly MixedConcrete by the Pressure MethodC470/C4
9、70M Specification for Molds for Forming ConcreteTest Cylinders VerticallyC918/C918M Test Method for Measuring Early-Age Com-pressive Strength and Projecting Later-Age StrengthC1064/C1064M Test Method for Temperature of FreshlyMixed Hydraulic-Cement ConcreteC1231/C1231M Practice for Use of Unbonded C
10、aps inDetermination of Compressive Strength of Hardened Cy-lindrical Concrete Specimens3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology C125.4. Summary of Practice4.1 Molded concrete cylindrical specimens are cured underconditions that increase
11、the early-age concrete temperature andthe rate of hydration. This permits the specimens to develop asignificant portion of their ultimate properties within a timeperiod ranging from 24 to 49 h, depending upon the procedureused. In Procedure A, specimens are stored in a warm waterbath for 24 h. In Pr
12、ocedure B, specimens are stored for 48 h ininsulated curing containers in which the elevated curingtemperature is obtained from heat of hydration of the cement.If specimens are to be used for estimating strength potential inaccordance with Test Method C918/C918M, specimen tem-perature is monitored d
13、uring the accelerated curing period.4.2 Table 1 summarizes important characteristics of thesecuring procedures.1This 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 e
14、dition approved March 15, 2017. Published May 2017. Originallyapproved in 2012. Last previous edition approved in 2012 as C1768/C1768M12.DOI: 10.1520/C1768_C1768M-12R17.2See Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual Book of ASTM Standards, Vol. 04.02.3For referen
15、ced ASTM standards, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Co
16、nshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade
17、Organization Technical Barriers to Trade (TBT) Committee.15. Significance and Use5.1 By increasing the concrete temperature, the rate ofhydration increases and a larger portion of the later-ageproperties of the concrete can be attained during the shortcuring period compared with standard temperature
18、 curing asdescribed in Practice C31/C31M and Practice C192/C192M.5.2 Specimens subjected to accelerated curing can be usedto estimate the later-age strength under standard-curing condi-tions by using this practice in conjunction with Test MethodC918/C918M. The temperature history of the test specime
19、ns isrecorded and the maturity index at the time of testing iscalculated. Based on the measured maturity index and theearly-age strength test results, the later age strength (such as at28 days) under standard curing can be estimated from apreviously established strength-maturity relationship for tha
20、tconcrete mixture. Thus accelerated curing procedures canprovide, at the earliest practical time, an indication of thepotential strength of the concrete sample. These early-agestrength tests also provide information on the variability of theproduction process for use in quality control, so that nece
21、ssaryadjustments in mixture proportions can be made in a timelymanner.5.3 The user shall select the procedure to use on the basis ofexperience and local conditions. These procedures, in general,will be practical if a field laboratory is available to house thecuring containers and the testing equipme
22、nt to measure com-pressive strength within the specified time limits.6. Apparatus6.1 Small Tools and EquipmentFor fabricating specimensshall conform to Practice C31/C31M or Practice C192/C192M,whichever is applicable.6.2 Cylinder MoldsShall conform to Specification C470/C470M. Paper molds are not pe
23、rmitted. Procedure B requiressingle-use molds.6.3 Curing Apparatus:6.3.1 Accelerated Curing Tank for Procedure A-Warm Wa-ter Method:6.3.1.1 The tank is of any configuration suitable for thenumber of cylinders to be cured. Arrange the cylinders in aconfiguration that provides a clearance of at least
24、50 mm 2 in.between the surface of each cylinder and the wall of the tank,and at least 100 mm 4 in. between adjacent cylinders.Maintain the water level at least 100 mm 4 in. above the topsof the cylinders.NOTE 1It may be convenient to have an overflow pipe for controllingthe water depth in the tank.
25、A number of different tanks have been usedsuccessfully. A schematic of a suitable curing tank is given in AppendixX1.6.3.1.2 Equip the tank with environmental control ele-ment(s) capable of: (1) maintaining the water temperature at 356 3C 95 6 5F at any point in the water; and (2) limiting thetemper
26、ature drop, after immersion of specimens, to less than3C 5F; and (3) returning to the specified water temperaturewithin 15 min after immersion of specimens. A temperaturerecording device, independent of the thermostat, is required tomonitor the water temperature.NOTE 2Depending upon the design featu
27、res of the tank, insulation ormechanical agitation, or both, might be necessary to meet the specifiedtemperature requirements. Electrical immersion heaters controlled by athermostat have been used successfully to meet the water temperaturerequirements. The size of the heating element(s) required wil
28、l dependupon the size of the tank and the number and size of specimens to be curedat one time. A lid may be provided to reduce evaporation and heat loss.6.3.1.3 The support for the specimens is designed to permitcirculation of water within the tank.6.3.2 Curing Container for Procedure B-Autogenous C
29、ur-ing Method:6.3.2.1 The container consists of thermal insulation thatsurrounds closely the concrete specimen or specimens. Anyconfiguration is acceptable provided the curing container meetsthe heat retention and other requirements of Annex A1.6.3.2.2 The container is capable of holding one or more
30、specimens.6.3.2.3 The container is capable of being opened to permitinsertion and withdrawal of the specimen(s) and has an outercasing and inner liner to protect the insulation from mechanicaldamage.6.3.2.4 The container has a temperature sensor that is notinsulated from the molded specimen. The tem
31、perature sensor isconnected to a data logger or other device for a continuousrecord of the temperature history within the container. Themaximum interval between temperature measurements is 30min.6.3.2.5 The container has a lid or other means to providesecure closure during the specified curing perio
32、d. The lidincludes a heat seal that satisfies the requirements of AnnexA1.NOTE 3Schematics of suitable containers are included in AppendixX1.7. Sampling7.1 Sample the freshly mixed concrete in accordance withPractice C172/C172M unless another procedure is required bythe purchaser of the testing serv
33、ices. If applicable, record thelocation where the sampled batch is placed in the structure.8. Slump, Air Content, and Temperature8.1 SlumpMeasure and record the slump in accordancewith Test Method C143/C143M of each sample of concretefrom which specimens are made.TABLE 1 Characteristics of Accelerat
34、ed Curing ProceduresProcedure MoldsAcceleratedCuringTemperatureC FDuration ofAcceleratedCuringAge atTestingA.Warm WaterReusable orsingle-use3595 23.5h30min24h15minB.AutogenousCuringSingle-use Initialconcretetemperatureaugmentedby heat ofhydration48h15min49h15minC1768/C1768M 12 (2017)28.2 Air Content
35、Measure and record the air content inaccordance with either Test Method C173/C173M or TestMethod C231/C231M. The concrete used in performing the aircontent test shall not be used in fabricating test specimens.8.3 TemperatureMeasure and record the concrete tem-perature in accordance with Test Method
36、C1064/C1064M.9. Procedure9.1 Procedure AWarm Water Method:9.1.1 Preparation of Curing TankActivate the heatingcontrol elements at least 1 h before the start of scheduledcuring of concrete cylinders to allow the temperature of thewater to stabilize.9.1.2 Preparation of Test Specimens:9.1.2.1 Mold the
37、 test specimens in accordance with therequirements of Practice C31/C31M or Practice C192/C192M,whichever is applicable.9.1.2.2 If the specimens are to be tested in accordance withTest Method C918/C918M, embed a temperature sensor intothe center of one of the specimens molded from each sample.Activat
38、e the temperature recording device. Maintain a recordof the concrete temperature during the curing period and untiltime of testing. The maximum interval between temperaturemeasurements is 30 min. If the specimens are not be tested inaccordance with Test method C918/C918M, monitor watertemperature in
39、 accordance with 9.1.3.4.9.1.3 Curing:9.1.3.1 If necessary, cover the top of the specimens with arigid plate or tight fitting lid to prevent loss of paste to thewater bath.9.1.3.2 Immediately after molding, place the specimens intothe curing tank (Note 4). Maintain the water at the time ofimmersion
40、and throughout the curing period at 35 6 3C 956 5F.NOTE 4Loss of paste can be mitigated by placing the cylinders intothe water slowly so as not to agitate the water.9.1.3.3 Curing time and specimen age are measured fromthe time the specimens are submerged. Record to the nearest 15min the time when s
41、pecimens are submerged.9.1.3.4 Record the temperature of the curing water continu-ously throughout the curing period. The maximum intervalbetween temperature measurements is 30 min.9.1.3.5 After curing for 23.5 h 6 30 min, remove thespecimens from the tank and remove the molds.9.1.4 Testing:9.1.4.1
42、If compressive strength is to be measured, test thespecimens in accordance with Test Method C39/C39M at age24 h 6 15 min.NOTE 5The use of unbonded caps in accordance with PracticeC1231/C1231M is a practicable approach for meeting the time limitrequirements between end of curing and testing. The hard
43、ness of the padsis selected based on the anticipated strength at the time of testing.9.2 Procedure BAutogenous Curing Method:9.2.1 Preparation of Test Specimens:9.2.1.1 Mold the test specimens in accordance with therequirements of Practice C31/C31M or Practice C192/C192M,whichever is applicable. Use
44、 single-use molds.9.2.1.2 If the specimens are to be tested in accordance withTest Method C918/C918M, embed a temperature sensor intothe center of one of the molded specimens for each sample.Activate the temperature recording device. Maintain a recordof the concrete temperature during the curing per
45、iod and untiltime of testing. The maximum interval between temperaturemeasurements is 30 min.9.2.1.3 If the specimens are not to be tested in accordancewith Test Method C918/C918M, maintain a record of thetemperature measured by the sensor in the container. Themaximum interval between temperature me
46、asurements is 30min.9.2.2 Curing:9.2.2.1 Immediately after molding the specimen, cover themold with a tight-fitting cap and place the specimen into theautogenous curing container.NOTE 6It may be helpful to use a heavy-duty plastic bag to serve asa lifting grip for placing and removing the specimen f
47、rom the curingcontainer.9.2.2.2 Secure the container lid and turn on the temperaturerecording device.9.2.2.3 Curing time and specimen age are measured fromthe time the specimens are placed in the container. Record tothe nearest 15 min the time when specimens are placed in thecontainer.9.2.2.4 Store
48、the curing container for at least 12 h in alocation not subject to disturbance or direct sunlight. Theambient temperature shall be 21 6 6C 70 6 10F.9.2.2.5 At an elapsed time of 48 h 6 15 min from when thespecimen was placed in the curing container, remove thespecimen from the container and remove t
49、he mold. Allow thespecimens to stand at room temperature for at least 30 min.9.2.3 Testing:9.2.3.1 If compressive strength is to be measured, test thespecimens in accordance with Test Method C39/C39M at 49 h6 15 min (see Note 5).10. Report10.1 Report the following information for each cylinder tothe agency that will test the specimens:10.1.1 Identification number.10.1.2 Location where concrete represented by the samplewas placed, if applicable.10.1.3 Slump, air content, concrete temperature, and resultsof any other tests on the fresh c
