ASTM A1081 A1081M-2012 Standard Test Method for Evaluating Bond of Seven-Wire Steel Prestressing Strand《七股预应力钢绞线粘合评估的标准试验方法》.pdf

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1、Designation: A1081/A1081M 12Standard Test Method forEvaluating Bond of Seven-Wire Steel Prestressing Strand1This standard is issued under the fixed designation A1081/A1081M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year

2、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. Scope1.1 This test method describes procedures for determiningthe bond of seven-wire steel prestressing strand. The bonddete

3、rmined by this test method is stated as the tensile forcerequired to pull the strand through the cured mortar in acylindrical steel casing. The result of the test is the tensile forcemeasured on the loaded-end of the strand corresponding to amovement of 0.1 in. (2.5 mm) at the free-end of the strand

4、.1.2 This test method is applicable either in inch-pound units(as Specification A1081) or SI units (as SpecificationA1081M).1.3 The values stated in either inch-pound units or in SIunits are to be regarded separately as standard. Within the text,SI units are shown in brackets. The values stated in e

5、achsystem may not be exact equivalents; therefore, each systemshall be used independently of the other. Combining valuesfrom the two systems may result in non-conformance with thespecification.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I

6、t 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 Documents2.1 ASTM Standards:2A416/A416M Specification for Steel Strand, UncoatedSeven-Wire for Prestressed C

7、oncreteC33/C33M Specification for Concrete AggregatesC109/C109M Test Method for Compressive Strength ofHydraulic Cement Mortars (Using 2-in. or 50-mm CubeSpecimens)C150/C150M Specification for Portland CementC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryC1437 Test

8、 Method for Flow of Hydraulic Cement Mortar3. Terminology3.1 Definitions:3.1.1 bondthe adhesion of strand to concrete or mortar.3.1.2 bond breakera product wrapped around strand toprevent strand-to-concrete bond over the installed length.Extruded polystyrene foam pipe insulation is commonly usedfor

9、this purpose.3.1.3 manufactured lengtha length of strand that is manu-factured in one continuous length.3.1.4 mortara mixture of cement, fine aggregate (that is,sand) and water.3.1.5 strandall references to strand in this test methodshall be interpreted to be Specification A416/A416M seven-wire pres

10、tressing steel strand with nominal diameters of 0.500in. 12.70 mm or 0.600 in. 15.24 mm.3.1.6 test specimenan assembly consisting of one steelcasing, one sample of strand and mortar.4. Summary of Test Method4.1 Six samples of seven-wire steel prestressing strand withnominal diameters of 0.500 in. 12

11、.7 mm or 0.600 in. 15.24mm are selected from a single continuous length. Each of thesix strand samples are individually cast in a steel cylindercasing with a specified cement mortar.The strand is exposed onboth ends of the cylinder with a designated loaded-end andfree-end. Once the mortar reaches a

12、specified compressivestrength, the cylinder with the embedded steel strand is loadedinto a tensile testing machine. The designated loaded-end ofthe steel strand is gripped by the tensile testing machine andpulled away from the cylinder at a specified displacement rate.The tensile force on the loaded

13、-end of the strand is measuredalong with the corresponding displacement of the free-end. Theresult of the test is the tensile force measured at the loaded-endof the strand corresponding to a movement of 0.1 in. 2.5 mmat the free-end of the strand. The results of each sample test inthe set of six are

14、 reported individually and as an average.1This test method is 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. 15, 2012. Published January 2013. DOI: 10

15、.1520/A1081_A1081M.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.Copyright ASTM International, 100 Barr Har

16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 Prestressing steel strand is used in pre-tensioned andpost-tensioned concrete construction.5.2 In pre-tensioned concrete applications, the prestressingsteel strand is expected to transfer prestressing

17、forces to thestructural member via the adhesion (that is, bond) of theexposed wire strand surfaces to the surrounding cementitousmaterial.5.3 Manufacturing processes, subsequent handling, andstorage conditions can influence the strand bond.5.4 Prestressing steel strand is used in construction applic

18、a-tions with a variety of concrete mixtures. Developing tests andthreshold values for the performance of the strand in each ofthese unique mixtures is impractical.6. Apparatus6.1 A dial gauge or position transducer with a minimumprecision of 0.001 in (0.025 mm).6.2 A tensile testing machine with the

19、 following function-ality:6.2.1 Controlled loading rate based on cross-head displace-ment.6.2.2 Gripping device without torsional restraint. The lackof torsion restraint and satisfaction of this requirement shall beverified by demonstrating the ability to twist the actuator or thetest specimen by ha

20、nd or by manual lever. (Note 1)NOTE 1In testing to develop the test method, hydraulic actuators wereemployed to apply tension force to the strand. The nature of the hydraulicactuators generally allows the piston to rotate with minimal resistance(since the piston floats on hydraulic fluid). Neither a

21、 roller bearing nor aball bearing is required though one may be necessary if the pull-out forceis applied through a mechanism where twist is restrained.7. Sampling of Strand7.1 Six samples of prestressing steel strand are needed forthis test. Each sample shall be at least 32 in. 800 mm long.7.2 Samp

22、les shall be collected from the same reel or reellesspack of strand (typically 3.5 tons 3 metric tons) or the samemanufactured length of strand (typically 2028 tons 1825metric tons).7.3 The surface condition of the strand samples shall berepresentative of the strand intended for use in bonded appli-

23、cations. Care shall be taken to prevent the introduction ofsurface contaminants which may alter the bond performance ofthe strand. For qualification of a manufacturing process,sample surface shall be in the as-manufactured condition.8. Mortar Requirements8.1 Materials:8.1.1 SandThe sand shall confor

24、m to Specification C33/C33M requirements for fine aggregate. The sand shall comefrom natural sources. Manufactured sand shall not be permit-ted.8.1.2 CementThe cement shall conform to SpecificationC150/C150M requirements for Type III cement.8.1.3 WaterThe water shall be potable.8.2 Mortar Preparatio

25、nThe preparation of the materialsand procedure used to mix the mortar shall be performed inconformance with Practice C192/C192M (Note 2) with thefollowing exceptions:8.2.1 Aggregates, other than sand, shall not be used.8.2.2 Admixtures shall not be used.8.3 Mortar Performance RequirementsThe mortar

26、shallbe tested in conformance with Practice C192/C192M with thefollowing exceptions and additional requirements.8.3.1 SlumpNo measurements required.8.3.2 Air ContentNo measurements required.8.3.3 FlowMortar flow shall be measured in accordancewith the procedures in Test Method C1437. The flow rate s

27、hallbe greater than or equal to 100 % but shall not exceed 125 %.8.3.4 StrengthMortar strength shall be evaluated in con-formance with Test Method C109/C109M using 2 in. 50 mmmortar cubes. Before starting the test and after a minimum of22 hours curing time, mean mortar cube strength shall not beless

28、 than 4 500 psi 31 MPa. During performance of the strandbond test and within 24 hours 6 2 hours of mortar mixing,mean mortar cube strengths shall be between 4 500 psi 31MPa and 5 000 psi 34.5 MPa (Note 3).NOTE 2Practice C192/C192M is described as a standard practice to beused for concrete test speci

29、mens. As outlined in 8.1, only fine aggregates(that is, sand) are included in the mixture along with cement and water.Because coarse aggregates are not included, this mixture is defined as“mortar” and not “concrete.” Aside from this difference and a few otherexceptions noted in Section 8, the practi

30、ces documented in PracticeC192/C192M are to be applied when making the mortar used in this testmethod.NOTE 3The ability to consistently achieve the specified mortarstrengths can be a challenge for testing facilities with limited mortarexperience and/or limited mixing and curing facilities and multip

31、le trialbatches may be required to develop appropriate mixes. If mean mortarstrengths are less than the 4 500 psi 31 MPa when the strand bond testis performed, the strand bond test results will be biased to provide lowerbond test values than if the mortar was within the specified range. For thepurpo

32、se of comparing the bond test results of this test method against aminimum threshold value, a bond test result that exceeds a minimumthreshold value with a mean mortar strength less than 4 500 psi 31 MPashould be accepted as meeting a specified minimum threshold value.If mortar strengths are greater

33、 than the 5 000 psi 34.5 MPa when thestrand bond test is performed, the strand bond test results will be biased toprovide higher bond test values than if the mortar was within the specifiedrange. For the purpose of comparing the bond test results of this testmethod against a minimum threshold value,

34、 a bond test result that is belowa minimum threshold value with a mean mortar strength greater than 5 000psi 34.5 MPa should be considered as failing to meet the specifiedminimum threshold value.9. Preparation of Test Specimens9.1 Materials:9.1.1 Strand SamplesStrand sample requirements are de-fined

35、 in Section 7.9.1.2 MortarMortar requirements are defined in Section8.9.1.3 Bond BreakerA 1 in. 6 0.25 in. 25 mm 6 6 mmoutside diameter2in.6 0.08 in. 50 mm 6 2 mm lengthsection of pipe insulation or equivalent material shall be usedas a bond breaker. The position of the bond breaker shall be asdefin

36、ed in Fig. 1 (Note 4).A1081/A1081M 1229.1.4 Steel CasingEach individual test specimen of strandshall be cast in a 5 in. 130 mm outside diameter 18 in. 450mm long cylindrical steel casing as defined in Fig. 1. Thethickness of the cylindrical walls of the steel casing shall not beless than 11 gage or

37、0.119 in. 3.0 mm. A 6 in. 6 in. 0.25in. 150 mm 150 mm 6 mm square plate with a58 in. 16mm hole located at the center of the plate to accommodate thestrand shall be welded to the bottom of the casing. A 50durometer 6 in. 6 in. 0.5 in. 6 0.125 in. 150 mm 150mm 12.5 mm 6 3 mm polychloroprene pad with a

38、58 in. 16mm diameter hole or slit sufficient to accommodate the strandshall be located between the plate and bearing. (Note 5) Theother dimensions of the steel casing and the strand areindicated on the diagram. The steel casing shall have sufficientrigidity to prevent radial cracking visible to norm

39、al or cor-rected vision in the concrete mortar during testing.*SI equivalent: 50 mm 6 2.0 mm*SI equivalent: 64 mm 6 13 mm* SI equivalent: 450 mm 6 6.4 mm* SI equivalent: 800 mm +250 mm 0 mm*SI equivalent: 130 mm 6 3 mm (OD) 3 mm min (wall thickness)NOTE 1The “Electronic End Slip Measurement” apparat

40、us shown here is an example of one type of measurement set-up. Other configurations anddevices can be used. A mold release agent may be sprayed onto the canister ID walls before pouring mortar.FIG. 1 Longitudinal Cross-Section Diagram of Strand Test Specimen in a Mortar-Filled CylinderA1081/A1081M 1

41、239.2 Specimen AssemblyEach individual test specimenshall be made by casting one single strand concentrically in thesteel casing with the mortar. The test specimen shall be castwith the longitudinal axis of the strand and the steel casing inthe vertical position. Temporary jigs shall be used to keep

42、 thestrand sample concentrically centered 612 in. 13 mm in thesteel casing and to prevent longitudinal movement duringmortar installation and consolidation. The temporary jigs canbe removed after the mortar has cured and prior to testing.9.3 ConsolidationAfter the cylinder is approximately50 % fille

43、d with mortar, the test specimens shall be mechani-cally consolidated by vibration in conformance with PracticeC192/C192M. The mortar shall be consolidated to ensure thata normal amount of air voids exist at the interface between thestrand and the surrounding concrete mortar (see Note 6). Oncethe in

44、itial addition of mortar is consolidated, the next 40 % ofmortar shall be added to the steel casing and again mechani-cally consolidated by vibration in conformance with PracticeC192/C192M. Once the mortar is consolidated the secondtime, the remaining 10 % of mortar shall be added to the steelcasing

45、 until a smooth, level mortar surface is achieved at thetop of the casing.9.4 CuringOnce all six test specimens and mortar cubeshave been cast, curing of the mortar shall occur in conformancewith Practice C192/C192M. The concrete mortar shall be curedin a controlled environment with the following co

46、nditions:9.4.1 Curing TemperatureCuring temperatures shall be73.4F 6 3F 23C 6 2C.9.4.2 Curing Relative HumidityAverage hourly relativehumidity during curing shall be maintained above 90 %.9.4.3 VibrationThe test specimens shall be cured in anenvironment free of vibrations.NOTE 4Variances in the leng

47、th of the bond breaker can causesignificant variance in the results of this test method. Careful attention tothe dimensions, installation and position of the bond breaker during andafter the addition of the mortar is essential.NOTE 5The polychloroprene pad helps control the force loading rateand can

48、 provide a better surface to allow for minor centering correctionsas load is applied to the cylinder.NOTE 6Excessive air voids can cause erroneous test results becauseair voids reduce the available bonding surface between the concretemortar and the strand.10. Test Set-up10.1 Test FrameThe test speci

49、mens shall be placed intothe test frame with the capabilities as defined in Section 6. Theload shall be measured as applied to the loaded-end.10.2 Free-End Slip MeasurementA position transducer ordial gauge shall be installed capable of measuring the move-ment of the free-end of the strand relative to the hardenedmortar or the steel casing. Fig. 1 shows an example of one typeof measurement apparatus. The measuring device shall mea-sure free-end strand mo