1、Designation: A944 10Standard 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 the case of revis
2、ion, 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. Scope*1.1 This test method describes procedures to establish therelative bond strength of steel reinforcing ba
3、rs 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 obtained using this tes
4、t 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 testmethod should only
5、 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 considered standard
6、.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 use.2. Referenced
7、Documents2.1 ASTM Standards:2A775/A775M Specification for Epoxy-Coated Steel Rein-forcing BarsC192/C192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryE4 Practices for Force Verification of Testing MachinesE575 Practice for Reporting Data from Structural Tests ofBuilding Con
8、structions, Elements, Connections, and As-semblies3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 bond strength, nmaximum measured load in atensile bond test of a steel reinforcing bar.3.1.2 bonded length, nthe length of the test bar that is incontact with concrete.3.1.3 concr
9、ete 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 and thebonded length.
10、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 perimeterand the center-to-ce
11、nter 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 accuracy within 62 %
12、 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.1This test method is
13、under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.05 on Steel Reinforcement.Current edition approved Nov. 1, 2010. Published December 2010. Originallyapproved in 1995. Last previous edition approved in 2005 as
14、 A944 05. DOI:10.1520/A0944-10.2For 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.1*A Summary of Changes section
15、 appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 Compression Reaction PlateThe compression reac-tion plate shall be placed a minimum clear distance equal to 0.9lemeasured from the center of the
16、test bar to the edge of thereaction plate.4.3 Bar Displacement MeasurementsDisplacements ofthe loaded and free ends of the steel reinforcing bar shall bemeasured with respect to the loaded and free surfaces, respec-tively, of the concrete using suitable measurement devices.Dial gages having the smal
17、lest division of not more than 25 m0.001 in. or linear variable differential transformers (LVDTs)with equal or superior accuracy are examples of satisfactorydevices.5. Test Specimen5.1 Beam-End SpecimenThe test specimen shall consistof the test bar cast in a block of reinforced concrete 600 6 25mm 2
18、4 6 1 in. long by db+ 200 6 13 mm db+8612 in.wide by a minimum of db+Cb+le+60mmdb+Cb+le+212in. 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
19、 to the test bar, as shown in Fig. 2.Transverse 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 us
20、ed as bond breakers to control the bonded length 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 the
21、test; alternatively, access to the free end of 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 b
22、e fabricated fromFIG. 1 Schematic of Test ApparatusA944 102Grade 420 Grade 60 No. 10 No. 3 bars for test bars up toand including No. 25 No. 8 and No. 13 No. 4 bars for testbars larger than No. 25 No. 8. The two flexural steelreinforcing bars shall be selected so as to provide a total areanot less th
23、an that of the test bar.NOTE 2The lead 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 FabricationT
24、he concrete block shall be fabricatedusing 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 vib
25、rator to ensure removal of entrappedair.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
26、 concretefrom a single ready-mix truck. 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 str
27、ength, as required by Specification A775/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
28、 rapid evaporation ofwater until the concrete 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 concre
29、te cylinders shall beprepared in accordance 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 T
30、est SpecimensA944 1037. Procedure7.1 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 a mini-mum, the initial load an
31、d displacement readings and themaximum 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 specific
32、ally include thefollowing:8.1.1 Dates 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, if re-quired, the relative rib area,8.1.4 Description of the steel reinforcing bar surface condi-tion an
33、d coating (if used): manufacturer, 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 mix de-sign, aggregate type, compressive strength at the time of test
34、(average of a minimum of two cylinders), 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 tes
35、t method, loading procedureused, the 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,
36、and8.1.12 Summary of findings.9. Precision 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 cu
37、rrently available. General guidelines 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-i
38、ng barsSUMMARY OF CHANGESCommittee A01 has identified the location of selected changes to this standard since the last issue (A944 05)that may impact the use of this standard. (Approved Nov. 1, 2010.)(1) Modified 5.1 to add an alternate method to provide accessto the free end of the test bar.ASTM In
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40、ly their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand s
41、hould be addressed to ASTM 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 S
42、tandards, at the address 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 ASTM website (www.astm.org/COPYRIGHT/).A944 104
