1、Designation: C 1231/C 1231M 07Standard Practice forUse of Unbonded Caps in Determination of CompressiveStrength of Hardened Concrete Cylinders1This standard is issued under the fixed designation C 1231/C 1231M; the number immediately following the designation indicates theyear of original adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers requirements for a capping systemusing unbonded caps fo
3、r testing concrete cylinders molded inaccordance with Practice C 31/C 31M or C 192/C 192M. 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. Abo
4、ve 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 acceptance testingof concrete with compressive strength below 1500
5、 psi 10MPa or above 12 000 psi 85 MPa.1.3 The values stated in either inch-pound or SI units shallbe regarded as standard. SI units are shown in brackets. Thatvalues stated in each system may not be exact equivalents;therefore, each system must be used independently of the other,without combining th
6、e values in any way.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 regulatory limitations prior to
7、 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:3C 31/C 31M Practice for Making a
8、nd Curing Concrete TestSpecimens in the FieldC 39/C 39M Test Method for Compressive Strength of Cy-lindrical Concrete SpecimensC 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryC 617 Practice for Capping Cylindrical Concrete Speci-mensD 2000 Classification System fo
9、r 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 cappingsystem in t
10、esting hardened concrete cylinders made in accor-dance with Practices C 31/C 31M or C 192/C 192M in lieu ofthe capping systems described in Practice C 617.4.2 The elastomeric pads deform in initial loading to con-form to the contour of the ends of the cylinder and arerestrained from excessive latera
11、l 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 to planen
12、ess requirementsof Test Method C 39/C 39M and the requirements of PracticeC 617. This may include grinding equipment or cappingmaterials and equipment to produce neat cement paste, highstrength gypsum plaster, or sulfur mortar caps.5.2 Elastomeric Pads:5.2.1 Pads shall be12 6116 in. 136 2 mm thick a
13、nd thediameter shall not be more than116 in. 2 mm smaller than theinside diameter of the retaining ring.5.2.2 Pads shall be made from polychloroprene (neoprene)meeting the requirements of Classification D 2000 as follows:1This practice is under the jurisdiction of ASTM Committee C09 on Concreteand C
14、oncreteAggregates and is the direct responsibility of Subcommittee C09.61 onTesting for Strength.Current edition approved July 15, 2007. Published August 2007. Originallyapproved in 1993. Last previous edition approved in 2006 as C 1231/C 1231M06.2Section on Safety Precautions, Manual of Aggregate a
15、nd Concrete Testing,Annual 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
16、.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Shore ADurometerClassification D 2000Line Call-Out50 M2BC51460 M2BC61470 M2BC714The tolerance on Shore A durometer har
17、dness is 6 5. Table1 provides requirements for use of caps made from materialmeeting the requirements of Classification D 2000, 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 wit
18、h 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 are placed in service, th
19、e pad durometer, and the numberof uses to which they have been subjected.5.3 Retainers, shall be made of metal that will prove durablein repeated use (Note 1). The cavity in the metal retainers shallhave a depth at least twice the thickness of the pad. The insidediameter of the retaining rings shall
20、 not be less than 102 % orgreater than 107 % of the diameter of the cylinder. The surfacesof the metal retainer which contact the bearing blocks of thetesting machine shall be plane to within 0.002 in. 0.05 mm.The bearing surfaces of the retainers shall not have gouges,grooves, or indentations great
21、er than 0.010 in. 0.25 mm deepor greater than 0.05 in.232 mm2 in surface area.NOTE 1Retainers made from steel and some aluminum alloys havebeen found acceptable. Retainer design and metals used are subject to theperformance and acceptance requirements of Section 8.6. Test Specimens6.1 The specimens
22、shall be either 6 by 12 in. 150 by 300mm or 4 by 8 in. 100 by 200 mm cylinders made inaccordance with Practices C 31/C 31M or C 192/C 192M.Neither end of a cylinder shall depart from perpendicularity tothe axis by more than 0.5 (approximately equivalent to18 in.in 12 in. 3 mm in 300 mm). No individu
23、al 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 cylindrical surface.An alternative metho
24、d is to place the end of the cylinder on a plane surfaceand support the try square on that surface.6.2 Depressions under a straight edge measured with around wire gage across any diameter shall not exceed 0.20 in.5 mm. If cylinder ends do not meet this tolerance, thecylinder shall not be tested unle
25、ss 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 a cap or caps meeting PracticeC 617, provided they meet the requirements of Section 5.7.2 Examine both sides of pads for excessive wear ordamage. Re
26、place pads that have cracks or splits in their top orbottom surface that exceed38 in. 10 mm in length regardlessof depth. Insert pad in the retainer before it is placed on thecylinder (Note 3).NOTE 3Some manufacturers recommend dusting the pads and theends of the cylinders with corn starch or talcum
27、 powder prior to testing.7.3 Center the unbonded cap or caps on the cylinder andplace the cylinder on the lower bearing block of the testingmachine. Carefully align the axis of the cylinder with thecenter of thrust of the testing machine by centering the upperretaining ring on the spherically seated
28、 bearing block. As thespherically seated block is brought to bear on the upperretaining ring, rotate its movable portion gently by hand so thatuniform seating is obtained. After application of load, butbefore reaching 10 % of the anticipated specimen strength,check to see that the axis of the cylind
29、er is vertical within atolerance of18 in. in 12 in. 3.2 mm in 300 mm and that theends of the cylinder are centered within the retaining rings. Ifthe cylinder alignment does not meet these requirements,release the load, check compliance with 6.1, and carefullyrecenter the specimen. Reapply load and r
30、echeck specimencentering and alignment. A pause in load application to checkcylinder alignment is permissible.7.4 Complete the load application, testing, calculation, andreporting of results in accordance with Test Method C 39/C 39M (see Note 4).NOTE 4Some users have reported damage to testing machi
31、nes fromthe sudden release of energy stored in the elastomeric pads.NOTE 5Because of the violent release of energy stored in pads, thebroken cylinder rarely exhibits conical fracture typical of capped cylindersand the sketches of types of fracture in Test Method C 39/C 39M are notdescriptive. Occasi
32、onally, unbonded capped cylinders may develop earlycracking, but continue to carry increasing load. For this reason cylindersmust be tested to complete failure.8. Qualification of Unbonded Capping Systems andVerification of Reuse of Pads8.1 Table 1 specifies the conditions under which polychlo-ropre
33、ne (neoprene) unbonded pads must 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.8.2 When qualification tests are required they must be madeby either the
34、 supplier or user of the unbonded pads. The user ofthe pads must retain a copy of the current 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 te
35、sted with ends ground or capped to meet require-ments of Test Method C 39/C 39M and Practice C 617.TABLE 1 Requirements for Use of Polychloroprene(Neoprene)PadsCylinder Compressive Strength,psi MPaShore ADurometerHardnessQualificationTests RequiredMaximumReusesALess than 1500 10 Not permitted1 500 t
36、o 6 000 10 to 40 50 None 1002 500 to 7 000 17 to 50 60 None 1004 000 to 7 000 28 to 50 70 None 1007 000 to 12 000 50 to 80 70 Required 50Greater than 12,000 80 Not permittedAMaximum number of reuses will be less if pads wear, crack or split. See 7.2.C 1231/C 1231M 0728.4 To be acceptable, tests must
37、 demonstrate that at a 95 %confidence level (a = 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 initia
38、l 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 lev
39、el 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 shal
40、l 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 2000 psi 14 MPa of the highest strengthlevel to be
41、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 t
42、he 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 Qualificatio
43、n 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
44、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 1000 psi 7 MPa (Note 8). More than onepair of cylinders can be made
45、 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 C 617 capped and unbonded capped specimensproduce equal strengths, the number of pairs of cylinders that will beneeded to demonstr
46、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
47、 that the range of strengths permitted in qualificationtesting to define the strength level is 1000 psi 7 MPa, but that in countingnumber of reuses only cylinders within a range of 2000 psi 14 MPa areincluded in the reuse count.NOTE 9Cylinders for qualification tests can be from pairs of cylinderste
48、sted 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, and compute the averagestrength of the cylinders with reference c
49、aps and the averagestrength of the cylinders with unbonded caps, as follows:di5 xpi2 xsi(1)xs5 xs11 xs21 xs3. 1 xsn!/nxp5 xp11 xp21 xp3. 1 xpn!/nwhere:di= difference in strength of a pair of cylinders computedas the strength of unbonded capped cylinder minusthe strength of the cylinder prepared according toPractice C 617 (may be positive or negative),xpi= cylinder strength using unbonded cap,xsi= cylinder strength using Practice C 617,n = number of pairs of cylinders tested for the strengthlevel,xs= average stre
