1、Designation: C1231/C1231M 14Standard Practice forUse of Unbonded Caps in Determination of CompressiveStrength of Hardened Concrete Cylinders1This standard is issued under the fixed designation C1231/C1231M; the number immediately following the designation indicates theyear of original adoption or, i
2、n the case of revision, the year 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. Scope*1.1 This practice covers requirements for a capping systemusing unbonded caps for tes
3、ting concrete cylinders molded inaccordance with Practice C31/C31M or C192/C192M. Un-bonded neoprene caps of a defined hardness are permitted tobe used for testing for a specified maximum number of reuseswithout qualification testing up to a certain concrete compres-sive strength level. Above that s
4、trength, level neoprene capswill require qualification testing. Qualification testing is re-quired for all elastomeric materials other than neopreneregardless of the concrete strength.1.2 Unbonded caps are not to be used for acceptance testingof concrete with compressive strength below 10 MPa 1500 p
5、si or above 80 MPa 12 000 psi.1.3 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 independently of the other. Combiningvalues from the two systems may
6、result in non-conformancewith the standard.1.4 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 and health practices and determine the applica-bility of regulato
7、ry limitations prior to use. (WarningConcrete cylinders tested with unbonded caps rupture moreviolently than comparable cylinders tested with bonded caps.The safety precautions given in the Manual of Aggregate andConcrete Testing are recommended.2)2. Referenced Documents2.1 ASTM Standards:3C31/C31M
8、Practice for Making and Curing Concrete TestSpecimens in the FieldC39/C39M Test Method for Compressive Strength of Cylin-drical Concrete SpecimensC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryC617 Practice for Capping Cylindrical Concrete SpecimensD2000 Classifica
9、tion System for Rubber Products in Auto-motive Applications3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 pad, nan unbonded elastomeric pad.3.1.2 unbonded cap, na metal retainer and an elastomericpad.4. Significance and Use4.1 This practice provides for using an unbonded capp
10、ingsystem in testing hardened concrete cylinders made in accor-dance with Practices C31/C31M or C192/C192M in lieu of thecapping systems described in Practice C617.4.2 The elastomeric pads deform in initial loading to con-form to the contour of the ends of the cylinder and arerestrained from excessi
11、ve lateral spreading by plates and metalrings to provide a uniform distribution of load from the bearingblocks of the testing machine to the ends of the concrete ormortar cylinders.5. Materials and Apparatus5.1 Materials and equipment necessary to produce ends ofthe reference cylinders that conform
12、to planeness requirementsof Test Method C39/C39M and the requirements of Practice1This practice is under the jurisdiction of ASTM Committee C09 on Concreteand ConcreteAggregates and is the direct responsibility of Subcommittee C09.61 onTesting for Strength.Current edition approved July 1, 2014. Publ
13、ished July 2014. Originally approvedin 1993. Last previous edition approved in 2013 as C1231/C1231M 13. DOI:10.1520/C1231_C1231M-14.2Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual Book of ASTM Standards, Vol 04.02.3For referenced ASTM standards, visit the ASTM website
14、, 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Driv
15、e, PO Box C700, West Conshohocken, PA 19428-2959. United States1C617. This may include grinding equipment or capping mate-rials and equipment to produce neat cement paste, highstrength gypsum plaster, or sulfur mortar caps.5.2 Elastomeric Pads:5.2.1 Pads shall be 13 6 2mm12 6116 in. thick and thedia
16、meter shall not be more than 2 mm 116 in. smaller than theinside diameter of the retaining ring.5.2.2 Pads shall be made from polychloroprene (neoprene)meeting the requirements of Classification D2000 as follows:Shore ADurometerClassification D2000Line Call-Out50 M2BC51460 M2BC61470 M2BC714The toler
17、ance on ShoreAdurometer hardness is 65. Table 1provides requirements for use of caps made from materialmeeting the requirements of Classification D2000, above.5.2.3 Other elastomeric materials that meet the performancerequirements of qualification tests in Section 8 are permitted.5.2.4 Elastomeric p
18、ads shall be supplied with the followinginformation:5.2.4.1 The manufacturers or suppliers name,5.2.4.2 The Shore A hardness, and5.2.4.3 The applicable range of concrete compressivestrength from Table 1 or from qualification testing.5.2.5 The user shall maintain a record indicating the date thepads
19、are placed in service, the pad durometer, and the numberof uses to which they have been subjected.5.3 Retainers, are a pair of metal fixtures used to providesupport for and alignment of the neoprene pads and thecylinder ends (Note 1 and Fig. 1). Each retainer (upper andlower) includes a (retaining)
20、ring that is welded to or manu-factured integrally with a base plate. The height of the retainingring shall be 25 6 3 mm 1.0 6 0.1 in. The inside diameterof the retaining ring shall not be less than 102 % or greater than107 % of the diameter of the cylinder. The thickness of theretaining ring shall
21、be at least 12 mm 0.47 in. for 150 mm 6in. diameter retainers and at least 9 mm 0.35 in. for 100 mm4 in. diameter retainers. The surface of the base plate thatcontacts the bearing block of the testing machine shall be planeto within 0.05 mm 0.002 in. The thickness of the base plateshall be at least
22、12 mm 0.47 in. for 150 mm 6 in. retainersand at least 8 mm 0.3 in. for 100 mm 4 in. retainers. Thebearing surfaces of the retainers shall not have gouges,grooves, protrusions, or indentations greater than 0.25 mm0.010 in. deep or greater than 32 mm20.05 in.2 in surfacearea.NOTE 1Retainers made from
23、steel and some aluminum alloys havebeen found acceptable.6. Test Specimens6.1 The specimens shall be either 150 by 300 mm 6 by 12in. or 100 by 200 mm 4 by 8 in. cylinders made inaccordance with Practices C31/C31M or C192/C192M. Nei-ther end of a cylinder shall depart from perpendicularity to theaxis
24、 by more than 0.5 (Note 2). No individual diameter of acylinder may differ from any other diameter by more than 2 %.NOTE 2One method of measuring the perpendicularly of ends ofcylinders is to place a try square across any diameter and measure thedeparture of the longer blade from an element of the c
25、ylindrical surface.An alternative method is to place the end of the cylinder on a plane surfaceand support the try square on that surface. A deviation from perpendicu-larity of 0.5 is equal to a slope of approximately 1 mm in 100 mm 18 in.in 12 in.6.2 Depressions under a straight edge measured with
26、around wire gage across any diameter shall not exceed 5 mm0.20 in. If cylinder ends do not meet this tolerance, thecylinder shall not be tested unless irregularities are correctedby sawing or grinding.7. Procedure7.1 Unbonded caps are permitted to be used on one or bothends of a cylinder in lieu of
27、a cap or caps meeting PracticeC617, provided the caps meet the requirements of Section 5.Pad hardness shall be in accordance with Table 1.NOTE 3The specified strength in the contract documents is for variousstages of construction. This may include strength test requirements forformwork removal or re
28、lease of prestress in addition to the test require-ments for verification of specified compressive strength. Therefore, padselection is based on the strength requirement for the designated stage ofconstruction.7.2 Replace pads that do not meet the dimensional require-ments of 5.2 or that exceed the
29、maximum reuse limits of Table1. Insert pad in the retainer before it is placed on the cylinder.NOTE 4Some manufacturers recommend dusting the pads and theends of the cylinders with corn starch or talcum powder prior to testing.7.3 Complete the load application, testing, calculation, andreporting of
30、results in accordance with Test Method C39/C39M.NOTE 5Some users have reported damage to testing machines fromthe sudden release of energy stored in the elastomeric pads.NOTE 6Occasionally, unbonded capped cylinders may develop earlycracking, but continue to carry increasing load. For this reason Te
31、stMethod C39/C39M requires cylinders to be loaded until it is certain thatthey have been compressed beyond their ultimate capacity.8. Qualification of Unbonded Capping Systems andVerification of Reuse of Pads8.1 Table 1 specifies the conditions under which polychlo-roprene (neoprene) unbonded pads m
32、ust be qualified under thissection depending on the concrete strength and the Shore Ahardness. Unbonded pads made of other elastomeric materialsmust be qualified using the procedures in this section.TABLE 1 Requirements for Use of Polychloroprene(Neoprene)PadsCompressive Strength,AMPapsiShore ADurom
33、eterHardnessQualificationTests RequiredMaximumReusesLess than 10 1 500 Not permitted10 to 40 1 500 to 6 000 50 None 10017 to 50 2 500 to 7 000 60 None 10028 to 50 4 000 to 7 000 70 None 10050 to 80 7 000 to 12 000 70 Required 50Greater than 80 12 000 Not permittedACompressive strength of concrete at
34、 age of testing as specified in ContractDocuments. For acceptance testing, it is the specified compressive strength fc.C1231/C1231M 1428.2 When qualification tests are required they must be madeby either the supplier or user of the unbonded pads. The user ofthe pads must retain a copy of the current
35、 qualification testreport to demonstrate compliance with this practice. See X1.1.8.3 The compressive strength of molded cylinders testedwith unbonded caps shall be compared with that of companioncylinders tested with ends ground or capped to meet require-ments of Test Method C39/C39M and Practice C6
36、17.8.4 To be acceptable, tests must demonstrate that at a 95 %confidence level ( = 0.05), the average strength obtainedusing unbonded caps is not less than 98 % of the averagestrength of companion cylinders capped or ground in accor-dance with 8.3.8.4.1 When required, qualification tests in accordan
37、ce with8.5 shall be made on initial use of an unbonded cap at both thehighest and lowest strength levels anticipated to establish anacceptable range of cylinder strength for use. In practiceindividual cylinders shall not have strengths more than 10 %greater than the high strength level or more than
38、10 % less thanthe low strength level qualified or specified in Table 1.Qualification tests shall be repeated whenever there is a changein the design or dimensions of the retaining rings, or whenthere is a change in pad composition or thickness, or the ShoreA hardness changes by more than five units.
39、 Initial qualifica-tion tests shall include verification that after the specifiedmaximum number of reuses the pads meet the requirements of8.4.8.4.2 When tests are made to establish a permissible numberof reuses exceeding those in Table 1, only those tests or reuseswhich are within 14 MPa 2000 psi o
40、f the highest strengthlevel to be qualified will be included in the reuse count.Laboratories must maintain records of the number of timespads are reused.NOTE 7Pad life depends on the hardness and type of pad material, thestrength of the concrete, the difference between the outside diameter of thecyl
41、inder and the inside diameter of the retaining ring, the unevenness androughness of the ends of the cylinder, and other factors. Based on availableinformation, scuffing or abrasion of the perimeter of the pad is normal,provided it does not reduce the thickness of the pad around the perimeter.8.5 Spe
42、cimen Preparation for Qualification and Pad ReuseTesting:8.5.1 Pairs of individual cylinders shall be made from asample of concrete and cured as nearly alike as possible: onecylinder per pair is to be tested after grinding or capping inaccordance with 8.3 and the other is to be tested using theunbon
43、ded cap system.8.5.2 A minimum of 10 pairs of cylinders shall be made atboth the highest and lowest strength levels desired or antici-pated (Note 8). The “strength level” is the average of thestrengths of the 20 or more cylinders whose strengths arewithin a range of 7 MPa 1000 psi (Note 9). More tha
44、n onepair of cylinders can be made from a single concrete sample,but cylinders must come from a minimum of two samplesmade on different days for each concrete strength level (Note10).NOTE 8If the Practice C617 capped and unbonded capped specimensproduce equal strengths, the number of pairs of cylind
45、ers that will beneeded to demonstrate compliance will range from 9 to more than 60FIG. 1 Example of Retaining Ring and Base PlateC1231/C1231M 143depending on the variability of test results. If the two capping systemsproduce equal strengths, about 10 % of laboratories will require more than60 tests
46、and 10 % of the laboratories will require 9 tests to demonstratestatistical compliance.NOTE 9Note that the range of strengths permitted in qualificationtesting to define the strength level is 7 MPa 1000 psi, but that in countingnumber of reuses only cylinders within a range of 14 MPa 2000 psi areinc
47、luded in the reuse count.NOTE 10Cylinders for qualification tests can be from pairs ofcylinders tested in routine laboratory operations and, in most instances,special trial batches should not be required for qualification tests.9. Calculation9.1 For each strength level, compute the difference instre
48、ngth for each pair of cylinders, and compute the averagestrength of the cylinders with reference caps and the averagestrength of the cylinders with unbonded caps, as follows:di5 xpi2 xsi(1)xs5xs11xs21xs31xsn!/nxp5xp11xp21xp31xpn!/nwhere:di= difference in strength of a pair of cylinders computedas th
49、e strength of unbonded capped cylinder minus thestrength of the cylinder prepared according to PracticeC617 (may be positive or negative),xpi= cylinder strength using unbonded cap,xsi= cylinder strength using Practice C617,n = number of pairs of cylinders tested for the strengthlevel,xs= average strength of Practice C617 capped cylinders fora strength level, andxp= average strength of unbonded cap cylinders for astrength level.9.2 Compute the average difference, d, and standard devia-
