1、Designation: A1081/A1081M 12A1081/A1081M 15Standard 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 revi
2、sion, 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 Scope*1.1 This test method describes procedures for determining the bond of seven-wire steel prestressi
3、ng strand. The bonddetermined by this test method is stated as the tensile force required to pull the strand through the cured mortar in a cylindricalsteel casing. The result of the test is the tensile force measured on the loaded-end of the strand corresponding to a movement of0.1 in. (2.5 mm)2.5 m
4、m at the free-end of the strand.1.2 This test method is applicable either in inch-pound units (as Specification A1081A1081) or SI units (as SpecificationA1081MA1081M).).1.3 The values stated in either inch-pound units or in SI units are to be regarded separately as standard. Within the text, SI unit
5、sare shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be usedindependently of the other. Combining values from the two systems may result in non-conformance with the specification.1.4 This standard does not purport to address all of the s
6、afety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A416/A416M Specification for Low
7、-Relaxation, Seven-Wire Steel Strand for Prestressed ConcreteC33/C33M Specification for Concrete AggregatesC109/C109M Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or 50-mm Cube Specimens)C150/C150M Specification for Portland CementC192/C192M Practice for Making and C
8、uring Concrete Test Specimens in the LaboratoryC670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction MaterialsC1437 Test 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 bre
9、akera product wrapped around strand to prevent strand-to-concrete bond over the installed length. Extrudedpolystyrene foam pipe insulation is commonly used for this purpose.3.1.3 manufactured lengtha length of strand that is manufactured in one continuous length.3.1.4 mortara mixture of cement, fine
10、 aggregate (that is, sand) and water.3.1.5 strandall references to strand in this test method shall be interpreted to be Specification A416/A416M seven-wireprestressing steel strand with nominal diameters of 0.500 in. 12.70 mm or 0.600 in. 15.24 mm.3.1.6 test specimenan assembly consisting of one st
11、eel casing, one sample of strand and mortar.1 This test method is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.05on Steel Reinforcement.Current edition approved Nov. 15, 2012Nov. 1, 2015. Published Janu
12、ary 2013January 2016. Originally approved in 2013. Last previous edition approved asA1081/A1081M 13. DOI: 10.1520/A1081_A1081M.10.1520/A1081_A1081M-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Stan
13、dardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible
14、 to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyrig
15、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 Six samples of seven-wire steel prestressing strand with nominal diameters of 0.500 in. 12.7 mm or 0.600 in. 15.24 mmare selected from a single continuous length. E
16、ach of the six strand samples are individually cast in a steel cylinder casing witha specified cement mortar. The strand is exposed on both ends of the cylinder with a designated loaded-end and free-end. Oncethe mortar reaches a specified compressive strength, the cylinder with the embedded steel st
17、rand is loaded into a tensile testingmachine. The designated loaded-end of the steel strand is gripped by the tensile testing machine and pulled away from the cylinderat a specified displacement rate. The tensile force on the loaded-end of the strand is measured along with the correspondingdisplacem
18、ent of the free-end. The result of the test is the tensile force measured at the loaded-end of the strand corresponding toa movement of 0.1 in. 2.5 mm at the free-end of the strand. The results of each sample test in the set of six are reportedindividually and as an average.5. Significance and Use5.
19、1 Prestressing steel strand is used in pre-tensioned and post-tensioned concrete construction.5.2 In pre-tensioned concrete applications, the prestressing steel strand is expected to transfer prestressing forces to thestructural member via the adhesion (that is, bond) of the exposed wire strand surf
20、aces to the surrounding cementitous material.5.3 Manufacturing processes, subsequent handling, and storage conditions can influence the strand bond.5.4 Prestressing steel strand is used in construction applications with a variety of concrete mixtures. Developing tests andthreshold values for the per
21、formance of the strand in each of these unique mixtures is impractical.6. Apparatus6.1 A dial gauge or position transducer with a minimum precision of 0.001 in (0.025 mm).in. 0.025 mm.6.2 A tensile testing machine with the following functionality:6.2.1 Controlled loading rate based on cross-head dis
22、placement.6.2.2 Gripping device without torsional restraint. The lack of torsion restraint and satisfaction of this requirement shall beverified by demonstrating the ability to twist the actuator or the test specimen by hand or by manual lever.lever (Note 1).NOTE 1In testing to develop the test meth
23、od, hydraulic actuators were employed 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 roller bearing nor a ball bearingis required though one may be necess
24、ary if the pull-out force is applied through a mechanism where twist is restrained.7. Sampling of Strand7.1 Six samples of prestressing steel strand are needed for this test. Each sample shall be at least 32 in. 800 mm long.7.2 Samples shall be collected from the same reel or reelless pack of strand
25、 (typically 3.5 tons 3 metric tons) or the samemanufactured length of strand (typically 2028 tons 1825 metric tons).7.3 The surface condition of the strand samples shall be representative of the strand intended for use in bonded applications.Care shall be taken to prevent the introduction of surface
26、 contaminants which may alter the bond performance of the strand. Forqualification of a manufacturing process, sample surface shall be in the as-manufactured condition.8. Mortar Requirements8.1 Materials:8.1.1 SandThe sand shall conform to Specification C33/C33M requirements for fine aggregate. The
27、sand shall come fromnatural sources. Manufactured sand shall not be permitted.8.1.2 CementThe cement shall conform to Specification C150/C150M requirements for Type III cement.8.1.3 WaterThe water shall be potable.8.2 Mortar PreparationThe preparation of the materials and procedure used to mix the m
28、ortar shall be performed inconformance with Practice C192/C192M (Note 2) with the following 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 shall be tested in conformance with Practice C192/C192M with th
29、efollowing 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 accordance with the procedures in Test Method C1437. The flow rate shall begreater than or equal to 100 % but shall not exceed 12
30、5 %.8.3.4 StrengthMortar strength shall be evaluated in conformance with Test Method C109/C109M using 2 in. 50 mm mortarcubes. Before starting the test and after a minimum of 22 hours curing time, mean mortar cube strength shall not be less than 4A1081/A1081M 152500 psi 31 MPa. During performance of
31、 the strand bond test and within 24 hours 6 2 hours of mortar mixing, mean mortar cubestrengths shall be between 4 500 psi 31 MPa and 5 000 psi 34.5 MPa (Note 3).NOTE 2Practice C192/C192M is described as a standard practice to be used for concrete test specimens.As outlined in 8.1, only fine aggrega
32、tes (thatis, sand) are included in the mixture along with cement and water. Because coarse aggregates are not included, this mixture is defined as “mortar” andnot “concrete.” Aside from this difference and a few other exceptions noted in Section 8, the practices documented in Practice C192/C192M are
33、 to beapplied when making the mortar used in this test method.NOTE 3The ability to consistently achieve the specified mortar strengths can be a challenge for testing facilities with limited mortar experience and/orlimited mixing and curing facilities and multiple trial batches may be required to dev
34、elop appropriate mixes. If mean mortar strengths are less than the4 500 psi 31 MPa when the strand bond test is performed, the strand bond test results will be biased to provide lower bond test values than if the mortarwas within the specified range. For the purpose of comparing the bond test result
35、s of this test method against a minimum threshold value, a bond testresult that exceeds a minimum threshold value with a mean mortar strength less than 4 500 psi 31 MPa should be accepted as meeting a specifiedminimum threshold value.If mortar strengths are greater than the 5 000 psi 34.5 MPa when t
36、he strand bond test is performed, the strand bond test results will be biased toprovide higher bond test values than if the mortar was within the specified range. For the purpose of comparing the bond test results of this test methodagainst a minimum threshold value, a bond test result that is below
37、 a minimum threshold value with a mean mortar strength greater than 5 000 psi 34.5MPa should be considered as failing to meet the specified minimum threshold value.9. Preparation of Test Specimens9.1 Materials:9.1.1 Strand SamplesStrand sample requirements are defined in Section 7.9.1.2 MortarMortar
38、 requirements are defined in Section 8.9.1.3 Bond BreakerA 1 in. 6 0.25 in. 25 mm 6 6 mm outside diameter 2 in. 6 0.08 in. 50 mm 6 2 mm length sectionof pipe insulation or equivalent material shall be used as a bond breaker. The position of the bond breaker shall be as defined inFig. 1 (Note 4).9.1.
39、4 Steel CasingEach individual test specimen of strand shall be cast in a 5 in. 130 mm outside diameter 18 in. 450mm long cylindrical steel casing as defined in Fig. 1. The thickness of the cylindrical walls of the steel casing shall not be lessthan 11 gage or 0.119 in. 3.0 mm. A 6 in. 6 in. 0.25 in.
40、 150 mm 150 mm 6 mm square plate with a 58 in. 16 mmhole located at the center of the plate to accommodate the strand shall be welded to the bottom of the casing. A 50 durometer 6in. 6 in. 0.5 in. 6 0.125 in. 150 mm 150 mm 12.5 mm 6 3 mm polychloroprene pad with a 58 in. 16 mm diameterhole or slit s
41、ufficient to accommodate the strand shall be located between the plate and bearing. (Note 5) The other dimensionsof the steel casing and the strand are indicated on the diagram. The steel casing shall have sufficient rigidity to prevent radialcracking visible to normal or corrected vision in the con
42、crete mortar during testing.9.2 Specimen AssemblyEach individual test specimen shall be made by casting one single strand concentrically in the steelcasing with the mortar. The test specimen shall be cast with the longitudinal axis of the strand and the steel casing in the verticalposition. Temporar
43、y jigs shall be used to keep the strand sample concentrically centered 6 12 in. 13 mm in the steel casing andto prevent longitudinal movement during mortar installation and consolidation. The temporary jigs can be removed after the mortarhas cured and prior to testing.9.3 ConsolidationAfter the cyli
44、nder is approximately 50 % filled with mortar, the test specimens shall be mechanicallyconsolidated by vibration in conformance with Practice C192/C192M. The mortar shall be consolidated to ensure that a normalamount of air voids exist at the interface between the strand and the surrounding concrete
45、 mortar (see Note 6). Once the initialaddition of mortar is consolidated, the next 40 % of mortar shall be added to the steel casing and again mechanically consolidatedby vibration in conformance with Practice C192/C192M. Once the mortar is consolidated the second time, the remaining 10 % ofmortar s
46、hall be added to the steel casing until a smooth, level mortar surface is achieved at the top of the casing.9.4 CuringOnce all six test specimens and mortar cubes have been cast, curing of the mortar shall occur in conformance withPractice C192/C192M. The concrete mortar shall be cured in a controll
47、ed environment with the following conditions:9.4.1 Curing TemperatureCuring temperatures shall be 73.4F 6 3F 23C 6 2C.9.4.2 Curing Relative HumidityAverage hourly relative humidity during curing shall be maintained above 90 %.9.4.3 VibrationThe test specimens shall be cured in an environment free of
48、 vibrations.NOTE 4Variances in the length of the bond breaker can cause significant variance in the results of this test method. Careful attention to the dimensions,installation and position of the bond breaker during and after the addition of the mortar is essential.NOTE 5The polychloroprene pad he
49、lps control the force loading rate and can provide a better surface to allow for minor centering corrections as loadis applied to the cylinder.NOTE 6Excessive air voids can cause erroneous test results because air voids reduce the available bonding surface between the concrete mortar andthe strand.10. Test Set-up10.1 Test FrameThe test specimens shall be placed into the test frame with the capabilities as defined in Section 6. The loadshall be measured as appl
