1、Designation: C1231/C1231M 15Standard Practice forUse of Unbonded Caps in Determination of CompressiveStrength of Hardened Cylindrical Concrete Specimens1This standard is issued under the fixed designation C1231/C1231M; the number immediately following the designation indicates theyear of original ad
2、option or, in 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
3、caps for testing concrete cylinders molded inaccordance with Practice C31/C31M or C192/C192M, or coresobtained in accordance with Test Method C42/C42M. Un-bonded neoprene caps of a defined hardness are permitted tobe used for testing for a specified maximum number of reuseswithout qualification test
4、ing up to a certain concrete compres-sive strength level. Above that strength, 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 accep
5、tance testingof concrete with compressive strength below 10 MPa 1500 psi 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
6、 independently of the other. Combiningvalues from the two systems may 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 sa
7、fety and health practices and determine the applica-bility of regulatory limitations prior to use. (WarningConcrete specimens tested with unbonded caps rupture moreviolently than comparable specimens tested with bonded caps.The safety precautions given in the Manual of Aggregate andConcrete Testing
8、are recommended.2)2. Referenced Documents2.1 ASTM Standards:3C31/C31M Practice for Making and Curing Concrete TestSpecimens in the FieldC39/C39M Test Method for Compressive Strength of Cylin-drical Concrete SpecimensC42/C42M Test Method for Obtaining and Testing DrilledCores and Sawed Beams of Concr
9、eteC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryC617 Practice for Capping Cylindrical Concrete SpecimensD2000 Classification System for Rubber Products in Auto-motive Applications3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 pad, nan unbo
10、nded 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 cappingsystem in testing hardened concrete cylinders made in accor-dance with Practices C31/C31M or C192/C192M, or coresobtained in accordance with
11、 Test Method C42/C42M in lieu ofthe capping 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 test specimens and arerestrained from excessive lateral spreading by plates and metalrings to provide a uniform distribution
12、 of load from the bearingblocks of the testing machine to the ends of the concrete ormortar specimens.1This 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 approv
13、ed Dec. 1, 2015. Published February 2016. Originallyapproved in 1993. Last previous edition approved in 2014 as C1231/C1231M 14.DOI: 10.1520/C1231_C1231M-15.2Section on Safety Precautions, Manual of Aggregate and Concrete Testing,Annual Book of ASTM Standards, Vol 04.02.3For referenced ASTM standard
14、s, 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM Internatio
15、nal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Materials and Apparatus5.1 Materials and equipment necessary to produce ends ofthe reference specimens that conform to planeness require-ments of Test Method C39/C39M and the requirements ofPractice C617. Thi
16、s may include grinding equipment or cap-ping materials and equipment to produce neat cement paste,high strength gypsum plaster, or sulfur mortar caps.5.2 Elastomeric Pads:5.2.1 Pads shall be 13 6 2mm12 6116 in. thick and thediameter shall not be more than 2 mm 116 in. smaller than theinside diameter
17、 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 tolerance on ShoreAdurometer hardness is 65. Table 1provides requirements for
18、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 pads shall be supplied with the followinginformation:5.2.4.1 The manufactu
19、rers 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 are placed in service, the pad durometer, and the numberof uses to which
20、they have been subjected.5.3 Retainers are a pair of metal fixtures used to providesupport for and alignment of the neoprene pads and the testspecimen ends (Note 1 and Fig. 1). Each retainer (upper andlower) includes a (retaining) ring that is welded to or manu-factured integrally with a base plate.
21、 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 specimen. For test specimenshaving nominal diameters of 100 mm 4 in. or less, thethickness of the retaining ring shall be
22、at least 9 mm 0.35 in.and the thickness of the baseplate shall be at least 8 mm 0.30in. For test specimens having nominal diameters greater than100 mm 4 in., the thickness of the retaining ring andbaseplate shall be at least 12 mm 0.47 in. The surface of thebaseplate that contacts the bearing block
23、of the testing machineshall be plane to within 0.05 mm 0.002 in. The bearingsurfaces of the retainers shall not have gouges, grooves,protrusions, or indentations greater than 0.25 mm 0.010 in.deep or greater than 32 mm20.05 in.2 in surface area.NOTE 1Retainers made from steel and some aluminum alloy
24、s havebeen found acceptable.6. Test Specimens6.1 Specimens shall be cylinders made in accordance withPractices C31/C31M or C192/C192M, or cores obtained inaccordance with Test Method C42/C42M.6.2 Depressions under a straight edge measured with around wire gage across any diameter shall not exceed 5
25、mm0.20 in. If the specimen ends do not meet this tolerance, thespecimen 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 test specimen in lieu of a cap or caps meeting PracticeC617, provided th
26、e caps meet the requirements of Section 5.Pad hardness shall be in accordance with Table 1.NOTE 2The specified strength in the contract documents is for variousstages of construction. This may include strength test requirements forformwork removal or release of prestress in addition to the test requ
27、ire-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 maximum reuse limits of Table1. Insert pad in t
28、he retainer before it is placed on the specimen.NOTE 3Some manufacturers recommend dusting the pads and theends of the specimens with corn starch or talcum powder prior to testing.7.3 Complete the load application, testing, calculation, andreporting of results in accordance with Test Method C39/C39M
29、.NOTE 4Some users have reported damage to testing machines fromthe sudden release of energy stored in the elastomeric pads.NOTE 5Occasionally, specimens tested with unbonded caps maydevelop early cracking, but continue to carry increasing load. For thisreason Test Method C39/C39M requires test speci
30、mens to be loaded untilit is certain that they have been compressed beyond their ultimatecapacity.8. Qualification of Unbonded Capping Systems andVerification of Reuse of Pads8.1 Table 1 specifies the conditions under which polychlo-roprene (neoprene) unbonded pads must be qualified under thissectio
31、n depending on the concrete strength and the Shore Ahardness. Unbonded pads made of other elastomeric materialsmust be qualified using the procedures in this section.8.2 When qualification tests are required they must be madeby either the supplier or user of the unbonded pads. The user ofthe pads mu
32、st retain a copy of the current qualification testreport to demonstrate compliance with this practice. See X1.1.TABLE 1 Requirements for Use of Polychloroprene(Neoprene)PadsCompressive Strength,AMPapsiShore ADurometerHardnessQualificationTests RequiredMaximumReusesLess than 10 1 500 Not permitted10
33、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 age of testing as specified in ContractDocuments. For acceptance testing, it is the sp
34、ecified compressive strength fc.C1231/C1231M 1528.3 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 C617.8.4 To be acceptable, tests mu
35、st 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 accordance with8.5 shall be made on initi
36、al 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 10 % less thanthe low strength le
37、vel 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. Initial qualifica-tion tests sha
38、ll 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 of the highest strengthlevel to be
39、 qualified will be included in the reuse count.Laboratories must maintain records of the number of timespads are reused.NOTE 6Pad life depends on the hardness and type of pad material, thestrength of the concrete, the difference between the outside diameter of thecylinder and the inside diameter of
40、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 Specimen Preparation for Qualificati
41、on 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 theunbonded cap system.8.5.2 A minimum of
42、 10 pairs of cylinders shall be made atboth the highest and lowest strength levels desired or antici-pated (Note 7). 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 8). More than onepair of cylinders can be mad
43、e from a single concrete sample,but cylinders must come from a minimum of two samplesmade on different days for each concrete strength level (Note9).NOTE 7If the Practice C617 capped and unbonded capped specimensproduce equal strengths, the number of pairs of cylinders that will beneeded to demonstr
44、ate compliance will range from 9 to more than 60depending on the variability of test results. If the two capping systemsproduce equal strengths, about 10 % of laboratories will require more than60 tests and 10 % of the laboratories will require 9 tests to demonstratestatistical compliance.NOTE 8Note
45、 that the range of strengths permitted in qualificationtesting to define the strength level is 7 MPa 1000 psi, but that in countingFIG. 1 Example of Retaining Ring and Base PlateC1231/C1231M 153number of reuses only cylinders within a range of 14 MPa 2000 psi areincluded in the reuse count.NOTE 9Cyl
46、inders for qualification tests can be from pairs of cylinderstested in routine laboratory operations and, in most instances, special trialbatches should not be required for qualification tests.9. Calculation9.1 For each strength level, compute the difference instrength for each pair of cylinders, an
47、d 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 the strength of unbonded capped cylin
48、der 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 cylin
49、ders fora strength level, andxp= average strength of unbonded cap cylinders for astrength level.9.2 Compute the average difference, d, and standard devia-tion of the difference, sd, for each strength level, as follows:d5d11d21dn!/n (2)sd5 (di2 d!2/n 2 1!#1/29.3 To comply with this practice the following relationshipmust be satisfied:xp$0.98 xs1tsd!/n!1/2(3)where t is the value of “students t” for (n 1) pairs at = 0.05 from the following table:(n 1) t( = 0.05)A9 1.83314 1.76119 1.7291
