1、Designation: A944 10 (Reapproved 2015)Standard Test Method forComparing Bond Strength of Steel Reinforcing Bars toConcrete Using Beam-End Specimens1This standard is issued under the fixed designation A944; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes procedures to establish therelative bond strength of ste
3、el reinforcing bars in concrete.1.2 This test method is intended to determine the effects ofsurface preparation or condition (such as bar coatings) on thebond strength of deformed steel reinforcing bars (of sizesranging from No. 10 to No. 36 No. 3 to No. 11) to concrete.1.3 The bond strengths obtain
4、ed using this test method arenot directly applicable to the design of reinforced concretemembers.NOTE 1The bond strengths obtained using this test method aregenerally higher than obtained in development or splice tests using beamswith the same embedment lengths. The results obtained using this testm
5、ethod should only be used for comparisons with results for otherreinforcing bars tested using this method.1.4 The values stated in inch-pound units are to be regardedas standard. The values given in brackets are mathematicalconversions to SI units that are provided for information onlyand are not co
6、nsidered standard.1.5 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 u
7、se.2. Referenced Documents2.1 ASTM Standards:2A775/A775M Specification for Epoxy-Coated Steel Rein-forcing BarsC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryE4 Practices for Force Verification of Testing MachinesE575 Practice for Reporting Data from Structural Tes
8、ts ofBuilding Constructions, Elements, Connections, and As-semblies3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bond strength, nmaximum measured load in a ten-sile bond test of a steel reinforcing bar.3.1.2 bonded length, nthe length of the test bar that is incontact with c
9、oncrete.3.1.3 concrete cover, nminimum distance between thesurface of the test bar and the top or bottom of the testspecimen.3.1.4 embedment length, nthe distance from the surface ofthe concrete test specimen to the installed end of the steelreinforcing bar. This equals the sum of the lead length an
10、d thebonded length.3.1.5 lead length, nthe length of the test bar that is not incontact with concrete but is between the surface of the concretetest specimen and the bonded length.3.1.6 relative rib area, nratio of the projected rib areanormal to bar axis to the product of the nominal bar perimetera
11、nd the center-to-center rib spacing.3.2 Symbols:Cb= Concrete cover, mm in.db= Nominal diameter of reinforcing bar, mm in.le= Embedment length, mm in.4. Apparatus4.1 EquipmentA schematic of a suitable testing system isshown in Fig. 1. The loading system shall be capable ofmeasuring the forces to an a
12、ccuracy within 62 % of theapplied load, when calibrated in accordance with Practices E4.The test system shall have sufficient capacity to preventyielding of its various components and shall ensure that theapplied tensile load remains parallel to the axis of the steelreinforcing bar during testing.4.
13、2 Compression Reaction PlateThe compression reac-tion plate shall be placed a minimum clear distance equal to 0.9lemeasured from the center of the test bar to the edge of thereaction plate.1This test method is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys a
14、nd is the direct responsibility of SubcommitteeA01.05 on Steel Reinforcement.Current edition approved Nov. 1, 2015. Published November 2015. Originallyapproved in 1995. Last previous edition approved in 2010 as A944 10. DOI:10.1520/A0944-10R15.2For referenced ASTM standards, visit the ASTM website,
15、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 Conshohocken, PA 19428-2959. United States14.3
16、 Bar Displacement MeasurementsDisplacements of theloaded and free ends of the steel reinforcing bar shall bemeasured with respect to the loaded and free surfaces,respectively, of the concrete using suitable measurement de-vices. Dial gages having the smallest division of not more than25 m 0.001 in.
17、or linear variable differential transformers(LVDTs) with equal or superior accuracy are examples ofsatisfactory devices.5. Test Specimen5.1 Beam-End SpecimenThe test specimen shall consist ofthe test bar cast in a block of reinforced concrete 600 6 25 mm24 6 1 in. long by db+ 200 6 13 mm db+8612 in.
18、 wideby a minimum of db+Cb+le+60mmdb+Cb+le+212 in.high. A typical test specimen is illustrated in Fig. 2. Thespecimen shall be reinforced by four closed stirrups orientedparallel to the sides of the specimen and two flexural steelreinforcing bars parallel to the test bar, as shown in Fig. 2.Transver
19、se steel reinforcing bars similar to those illustrated inFig. 2 may be used to aid in fabrication and testing. The test barshall extend from the front surface a distance that is compatiblewith the test system. Two polyvinyl chloride (PVC) pipes shallbe used as bond breakers to control the bonded len
20、gth of thebar and to avoid a localized cone-type failure of the concrete atthe loaded end of the specimen. The free end of the test barshall butt against a hollow steel conduit or other device toprovide access to the free end for measuring slip during thetest; alternatively, access to the free end o
21、f the test bar shall beprovided without the hollow steel conduit by extending theinterior PVC pipe to the end of the specimen. All specimens ina test series shall use the same method to provide access to thefree end of the bar. The closed stirrups shall be fabricated fromGrade 420 Grade 60 No. 10 No
22、. 3 bars for test bars up toand including No. 25 No. 8 and No. 13 No. 4 bars for testFIG. 1 Schematic of Test ApparatusA944 10 (2015)2bars larger than No. 25 No. 8. The two flexural steelreinforcing bars shall be selected so as to provide a total areanot less than that of the test bar.NOTE 2The lead
23、 length, shown in Fig. 2, is typically between 13 and100 mm 0.5 and 4 in. This unbonded region is used to prevent acone-type pullout failure at the surface of the concrete. Increases in leadlength generally result in an increase in bond strength.5.2 FabricationThe concrete block shall be fabricatedu
24、sing concrete designed to produce a strength at the time of testbetween 31 and 38 MPa 4500 and 5500 psi. The specimenshall be cast in approximately equal layers not exceeding 250mm 9 in. in depth. Each layer shall be adequately consoli-dated with an internal vibrator to ensure removal of entrappedai
25、r.NOTE 3The nominal maximum size course aggregate should be lessthan or equal to34 of the minimum clear space between reinforcement orbetween reinforcement and the concrete surface of the beam-end speci-men.NOTE 4The properties of concrete tend to vary, even for concretefrom a single ready-mix truck
26、. Therefore, the order of casting specimensshould be selected to limit differences in bond strength caused bydifferences in concrete from different portions of the same batch. Forexample, when this test is used to evaluate the effect of epoxy coatings onbond strength, as required by Specification A7
27、75/A775M, specimenscontaining epoxy-coated bars and uncoated bars should be alternatedduring casting.6. Conditioning6.1 Specimen Conditioning and CuringThe test specimenshall be cured in the forms using a curing compound or aplastic membrane, or both, to prevent rapid evaporation ofwater until the c
28、oncrete has attained a strength of at least 14MPa 2000 psi. Specimen conditioning and curing shall besuch that the concrete strength shall be between 31 and 38 MPa4500 and 5500 psi at the time of test, unless another concretestrength is required. Standard concrete cylinders shall beprepared in accor
29、dance with Practice C192/C192M using arepresentative sample of the concrete used to make the testspecimen. The concrete cylinders shall be cured adjacent to andin the same manner as the test specimen. A minimum of twotest cylinders are required.FIG. 2 Beam-End Test SpecimensA944 10 (2015)37. Procedu
30、re7.1 A tensile load shall be applied to the test bar, asillustrated in Fig. 1. The loading rate shall be such that failurewill not occur prior to 3 min after starting to load the testspecimens. Data recorded for a test shall include, as aminimum, the initial load and displacement readings and thema
31、ximum load.NOTE 5The load rate should be between 10 to 33 % of the bondstrength per min. At least 10 intermediate displacement and load readingsshould be taken.8. Report8.1 The report shall include the applicable informationlisted in Practice E575, and shall specifically include thefollowing:8.1.1 D
32、ates of test and report,8.1.2 Test sponsor and agency,8.1.3 Identification of the bars tested: size, grade, meandeformation height, mean deformation spacing, and, ifrequired, the relative rib area,8.1.4 Description of the steel reinforcing bar surface condi-tion and coating (if used): manufacturer,
33、trade name, andcoating designation,8.1.5 Description of the fabrication and testing procedures,if these deviated in any way from this test method,8.1.6 Description of the concrete used, including mixdesign, aggregate type, compressive strength at the time of test(average of a minimum of two cylinder
34、s), and age of theconcrete at the time of test,8.1.7 Moisture condition of the concrete at the time of test:saturated surface dry, air dry,8.1.8 Concrete cover, embedment length and lead length ofthe installed reinforcement, in mm in.,8.1.9 Description of the test method, loading procedureused, the
35、displacements measured at each load step, and theactual rate of loading,8.1.10 Individual maximum load value (bond strength), in Nlb, for each test specimen,8.1.11 Photographs, sketches, word descriptions, or combi-nations thereof, of the failure modes observed, and8.1.12 Summary of findings.9. Prec
36、ision and Bias9.1 No statement is made on the precision or bias of this testmethod since the test results indicate only whether there isconformance to given criteria and since no generally acceptedmethod for determining precision and bias of this test methodis currently available. General guidelines
37、 provided herein forthe specimens, instrumentation, and procedures make theresults intractable to calculation of meaningful values bystatistical analysis for precision and bias at this time.10. Keywords10.1 beam-end test; coatings; concrete bond; steel reinforc-ing barsASTM International takes no po
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40、STM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the addres
41、s shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 10 (2015)4
