1、Designation: C1768/C1768M 12Standard 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 of last revision.
2、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 thatincrease the rate of
3、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 shall be used indepe
4、ndently 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 safety an
5、d 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)2. Referenced Documents2.1 ASTM Standards:3C31/C31M Practice for Making and Cu
6、ring 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 Practice for Sampling Freshly Mixed Con-creteC1
7、73/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/C470M Specification for Molds for Forming C
8、oncreteTest 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 Caps inDetermination of Compressive Streng
9、th of Hardened Con-crete Cylinders3. 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 the early-age concrete temperature andthe rate of hyd
10、ration. 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 Procedure B, specimens are stored for 48 h ininsulated
11、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 during the accelerated curing period.4.2 Table 1 summa
12、rizes important characteristics of thesecuring procedures.5. 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
13、 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 Method1This test method is under the jurisdiction of ASTM Com
14、mittee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.61 on Testing for Strength.Current edition approved Dec. 1, 2012. Published January 2013. DOI: 10.1520/C1768_C1768M-12.2See Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual
15、 Book of ASTM Standards, Vol. 04.02.3For referenced 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 Internatio
16、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1C918/C918M. The temperature history of the test specimens isrecorded and the maturity index at the time of testing iscalculated. Based on the measured maturity index and theearly-age strength test results, the l
17、ater age strength (such as at28 days) under standard curing can be estimated from apreviously established strength-maturity relationship for thatconcrete mixture. Thus accelerated curing procedures canprovide, at the earliest practical time, an indication of thepotential strength of the concrete sam
18、ple. These early-agestrength tests also provide information on the variability of theproduction process for use in quality control, so that necessaryadjustments 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 con
19、ditions. These procedures, in general,will be practical if a field laboratory is available to house thecuring containers and the testing equipment to measure com-pressive strength within the specified time limits.6. Apparatus6.1 Small Tools and EquipmentFor fabricating specimensshall conform to Prac
20、tice C31/C31M or Practice C192/C192M,whichever is applicable.6.2 Cylinder MoldsShall conform to Specification C470/C470M. Paper molds are not permitted. 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 a
21、ny configuration suitable for thenumber of cylinders to be cured. Arrange the cylinders in aconfiguration that provides a clearance of at least 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 le
22、ast 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. 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 environment
23、al 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 thetemperature drop, after immersion of specimens, to less than3C 5F; and (3) returning to the specified water temperaturewithin 15 min after immersion of specimens.
24、 A temperaturerecording device, independent of the thermostat, is required tomonitor the water temperature.NOTE 2Depending upon the design features of the tank, insulation ormechanical agitation, or both, might be necessary to meet the specifiedtemperature requirements. Electrical immersion heaters
25、controlled by athermostat have been used successfully to meet the water temperaturerequirements. The size of the heating element(s) required will 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
26、.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 Cur-ing Method:6.3.2.1 The container consists of thermal insulation thatsurrounds closely the concrete specimen or specimens. Anyconfiguration is acceptable
27、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 morespecimens.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 pr
28、otect the insulation from mechanicaldamage.6.3.2.4 The container has a temperature sensor that is notinsulated from the molded specimen. The temperature sensor isconnected to a data logger or other device for a continuousrecord of the temperature history within the container. Themaximum interval bet
29、ween temperature measurements is 30min.6.3.2.5 The container has a lid or other means to providesecure closure during the specified curing period. The lidincludes a heat seal that satisfies the requirements of AnnexA1.NOTE 3Schematics of suitable containers are included in AppendixX1.7. Sampling7.1
30、Sample the freshly mixed concrete in accordance withPractice C172/C172M unless another procedure is required bythe purchaser of the testing services. If applicable, record thelocation where the sampled batch is placed in the structure.8. Slump, Air Content, and Temperature8.1 SlumpMeasure and record
31、 the slump in accordancewith Test Method C143/C143M of each sample of concretefrom which specimens are made.8.2 Air ContentMeasure 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 use
32、d in fabricating test specimens.8.3 TemperatureMeasure and record the concrete tem-perature in accordance with Test Method C1064/C1064M.9. Procedure9.1 Procedure AWarm Water Method:TABLE 1 Characteristics of Accelerated Curing ProceduresProcedure MoldsAcceleratedCuringTemperatureC FDuration ofAccele
33、ratedCuringAge atTestingA.Warm WaterReusable orsingle-use3595 23.5h30min24h15minB.AutogenousCuringSingle-use Initialconcretetemperatureaugmentedby heat ofhydration48h15min49h15minC1768/C1768M 1229.1.1 Preparation of Curing TankActivate the heatingcontrol elements at least 1 h before the start of sch
34、eduledcuring of concrete cylinders to allow the temperature of thewater to stabilize.9.1.2 Preparation of Test Specimens:9.1.2.1 Mold the 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
35、 accordance withTest Method C918/C918M, embed a temperature sensor intothe center of one of the specimens molded from each sample.Activate the temperature recording device. Maintain a recordof the concrete temperature during the curing period and untiltime of testing. The maximum interval between te
36、mperaturemeasurements is 30 min. If the specimens are not be tested inaccordance with Test method C918/C918M, monitor watertemperature in 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 thewa
37、ter bath.9.1.3.2 Immediately after molding, place the specimens intothe curing tank (Note 4). Maintain the water at the time ofimmersion 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 wate
38、r.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 specimens are submerged.9.1.3.4 Record the temperature of the curing water continu-ously throughout the curing period. The maximum intervalbetween temperature measu
39、rements 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 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 accordan
40、ce with PracticeC1231/C1231M is a practicable approach for meeting the time limitrequirements between end of curing and testing. The hardness 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.
41、2.1.1 Mold the test specimens in accordance with therequirements of Practice C31/C31M or Practice C192/C192M,whichever is applicable. Use 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 molde
42、d specimens for each sample.Activate 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.9.2.1.3 If the specimens are not to be tested in accordancewith Test M
43、ethod C918/C918M, maintain a record of thetemperature measured by the sensor in the container. Themaximum interval between temperature measurements 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 c
44、uring container.NOTE 6It may be helpful to use a heavy-duty plastic bag to serve asa lifting grip for placing and removing the specimen from 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
45、 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 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 e
46、lapsed time of 48 h 6 15 min from when thespecimen was placed in the curing container, remove thespecimen from the container and remove the 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
47、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, a
48、ir content, concrete temperature, and resultsof any other tests on the fresh concrete sample and anydeviations from referenced standard test methods.10.1.4 Date and time of molding.10.1.5 Name of technician who molded the cylinders.10.1.6 Accelerated curing procedure (A or B) that was used.10.1.7 Ti
49、me when cylinder was submerged for ProcedureA,or time when cylinder was placed in the curing container forProcedure B.10.1.8 Recorded temperature history.10.1.9 Any deviations from this practice.11. Keywords11.1 accelerated curing; compressive strength; concrete cyl-inders; early-age strength; potential strengthC1768/C1768M 123ANNEX(Mandatory Information)A1. REQUIREMENTS FOR AUTOGENOUS CURING CONTAINERS (PROCEDURE B)A1.1 Heat RetentionPlace a watertight cylinder mold intothe autogenous curing container. Fill the mold to within 5 mm1
