1、Designation: C 1399 07aStandard Test Method forObtaining Average Residual-Strength of Fiber-ReinforcedConcrete1This standard is issued under the fixed designation C 1399; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of residualstrength of a fiberreinforced concrete test beam. The averagere
3、sidual strength is computed using specified beam deflectionsthat are obtained from a beam that has been cracked in astandard manner. The test provides data needed to obtain thatportion of the loaddeflection curve beyond which a significantamount of cracking damage has occurred and it provides ameasu
4、re of postcracking strength, as such strength is affectedby the use of fiberreinforcement.1.2 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 practic
5、es and determine the applica-bility of regulatory limitations prior to use.1.3 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.2. Referenced Documents2.1 ASTM Standards:2C 31/C 31M Practice for Making and Curing Concrete TestSpecime
6、ns in the FieldC 42/C 42M Test Method for Obtaining and Testing DrilledCores and Sawed Beams of ConcreteC78 Test Method for Flexural Strength of Concrete (UsingSimple Beam with Third-Point Loading)C 172 Practice for Sampling Freshly Mixed ConcreteC 192/C 192M Practice for Making and Curing ConcreteT
7、est Specimens in the LaboratoryC 823 Practice for Examination and Sampling of HardenedConcrete in ConstructionsC 1609/C 1609M Test Method for Flexural Performance ofFiber-Reinforced Concrete (Using Beam With Third-PointLoading)3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 de
8、flectionmidspan deflection of the test beam ob-tained in a manner that excludes deflection caused by thefollowing: (1) the flexural test apparatus, (2) crushing andseating of the beam at support contact points, and (3) torsion ofthe beam; sometimes termed net deflection.3.1.2 initial loading curveth
9、e loaddeflection curve ob-tained by testing an assembly that includes both the test beamand a specified steel plate (Fig. 1); plotted to a deflection of atleast 0.25 mm (0.010 in.) (Fig. 3).3.1.3 reloading curvethe loaddeflection curve obtainedby reloading and retesting the pre-cracked beam, that is
10、, afterthe initial loading but without the steel plate. (Fig. 3)3.1.4 reloading deflectiondeflection measured during thereloading of the cracked beam and with zero deflectionreferenced to the start of the reloading.3.1.5 residual strengththe flexural stress on the crackedbeam section obtained by cal
11、culation using loads obtainedfrom the reloading curve at specified deflection values (SeeNote 1).NOTE 1Residual strength is not a true stress but an engineering stresscomputed using the flexure formula for linear elastic materials and gross(uncracked) section properties.3.1.6 average residual streng
12、ththe average stresscarry-ing ability of the cracked beam that is obtained by calculationusing the residual strength at four specified deflections.4. Summary of Test Method4.1 Cast or sawed beams of fiberreinforced concrete arecracked using the thirdpoint loading apparatus specified inTest Method C7
13、8modified by a steel plate used to assist insupport of the concrete beam during an initial loading cycle(Fig. 1). The steel plate is used to help control the rate ofdeflection when the beam cracks. After the beam has beencracked in the specified manner, the steel plate is removed andthe cracked beam
14、 is reloaded to obtain data to plot a reloadingloaddeflection curve. Load values at specified deflection1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.42 on Fiber-Reinforced Concrete.Current edi
15、tion approved Aug. 1, 2007. Published September 2007. Originallyapproved in 1998. Last previous edition approved in 2007 as C 139907.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume infor
16、mation, refer to the standards Document Summary page onthe ASTM website.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.FIG. 1 Schematic of a Suitable Apparatus Where
17、the Deflection Gage Support Frame is Seated on the BeamFIG. 2 Schematic of a Suitable Apparatus Where the Deflection Gage Support Frame is Clamped to the Beam SupportsC 1399 07a2values on the reloading curve are averaged and used tocalculate the average residual strength of the beam.5. Significance
18、and Use5.1 This test method provides a quantitative measure usefulin the evaluation of the performance of fiberreinforcedconcrete. It allows for comparative analysis among beamscontaining different fiber types, including materials, dimensionand shape, and different fiber contents. Results can be use
19、d tooptimize the proportions of fiberreinforced concrete mixtures,to determine compliance with construction specifications, toevaluate fiberreinforced concrete which has been in service,and as a tool for research and development of fiberreinforcedconcrete (See Note 2).NOTE 2Banthia and Dubey3compare
20、d results using this test methodwith residual strengths at the same net deflections using a test protocol thatis similar to that described in Test Method C 1609/C 1609M on 45 beamswith a single fiber configuration at proportions of 0.1, 0.3, and 0.5 % byvolume. The results by this test method were o
21、n average 6.4 % lower thanby the procedure of Test Method C 1609/C 1609M.5.2 Test results are intended to reflect either consistency ordifferences among variables used in proportioning the fiber-reinforced concrete to be tested, including fiber type (mate-rial), fiber size and shape, fiber amount, b
22、eam preparation(sawed or molded), and beam conditioning.5.3 In molded beams fiber orientation near molded surfaceswill be affected by the process of molding. For tests offiber-reinforced concrete containing relatively rigid or stifffibers of length greater than 40 mm (1.5 in.), the use of sawedbeams
23、 cut from samples with an initial width and depth of atleast 3 times the length of the fiber is required to minimizeeffects of fiber orientation. When sawed beams are employed,and to avoid the effects of fiber orientation, care shall beapplied to ensure that the flexural tensile surface of the beam
24、isa sawed surface.6. Apparatus6.1 Either Screw Gear or Hydraulic Testing Apparatus, withthe ability to control the rate of motion of the loading head andmeeting the requirements of Test Method C78.Aload cell witha 44.5 kN capacity (10,000 lbf) will generally be required.Closed-loop feed-back control
25、led deflection apparatus is notrequired.6.2 Flexural-Loading Beam-Support Apparatus, conform-ing to the requirements of Test Method C78.6.3 Load and DeflectionMeasuring Devices, such as loadcells and electronic transducers, capable of producing elec-tronic analog signals and having support apparatus
26、 located andarranged in a manner that provides determination of appliedload and mid-span deflection (See 3.1.5) of the beam. Measuredeflection using a device capable of measuring net deflection atthe beam midspan with a minimum resolution of 0.025 mm(0.001 in.) by one of the following alternative me
27、thods (SeeNote 3).NOTE 3The deflection measurement requires care in the arrangement3Banthia, N. and Dubey, A., “Measurement of Flexural Toughness of FiberReinforced Concrete Using a Novel Technique, Part I:Assessment and Calibration,”In Press, Materials Journal, American Concrete Institute.FIG. 3 Lo
28、ad-Deflection CurvesC 1399 07a3of displacement transducers in order to minimize extraneous contributionssuch as might be caused by seating or twisting of the specimen.Experience has shown that apparatus designed to support deflectionmeasuring devices that eliminate extraneous deflections is acceptab
29、le.Methods to accomplish this measurement use spring-loaded electronicdisplacement transducers mounted on suspension frames or supportframes as shown in Fig. 1.6.3.1 Three Electronic Transducers, mounted on a supportframe. The support frame positions the transducers along thecenterline of the top su
30、rface of the test beam at locations so asto contact the beam at mid-span and each support location.Average the measured support deflections and subtract thisvalue from the recorded mid-span deflection to obtain the netdeflection.6.3.2 Two Electronic Transducers, mounted on a supportframe. The suppor
31、t frame either (1) surrounds the test beamand is clamped to the sides of the beam at points on a linepassing vertically through the beam support locations, or (2)isseated on top of the beam and is itself supported at pointsdirectly over the beam supports. In each case one transducer islocated on eac
32、h side of the test beam at mid-span, recordingdeflection between the mounted transducers and contact pointsthat are rigid attachments located on the beam at the center ofthe span. The average of the transducer measurements are thenet deflection.6.4 Data Acquisition Equipment, capable of simultaneous
33、lyrecording data from the load and deflection transducers byeither of the following alternative methods.6.4.1 X-Y Plotter, driven by analog signals from load anddeflection transducers to record the loaddeflection curve.6.4.2 Analog Signal Sampling and Digital Conversion Us-ing Automatic Data Acquisi
34、tion Equipment With a MinimumSampling Frequency of 2.5 Hz, to record load and correspond-ing deflection values from which loaddeflection curves can beproduced.6.5 Stainless Steel Plate, nominally 100 by 12 by 350 mm (4by12 by 14 in.) (See Note 4)NOTE 4Depending upon the chosen method for obtaining n
35、et deflec-tion during testing, a center hole may be placed in the steel plate toaccommodate placing a displacement transducer probe directly against thebottom of the test beam.6.6 Mechanical Dial Gage, with 0.025 mm (0.001 in.)resolution.6.7 MagneticMount Dial Gage Holder.6.8 Beam Molds, conforming
36、to the requirements of Prac-tice C 192/C 192M that will produce 100 mm by 100 mm by350 mm (4 in. by 4 in. by 14 in.) beams.7. Sampling, Test Beams, and Test Units7.1 Prepare a set of at least five beams from each sample offresh or hardened concrete.7.2 Freshly Mixed Concrete:7.2.1 Obtain samples of
37、freshly mixed fiberreinforcedconcrete in accordance with Practice C 172.7.2.2 Mold beams in accordance with Practice C 31/C 31Mor Practice C 192/C 192M and cast in one layer using avibrating table for consolidation. Internal vibration or roddingmay produce nonuniform fiber distribution.7.2.3 Cure sa
38、mples for a minimum of 7 days in accordancewith the standard curing procedure in Practice C 31/C 31M orthe procedure in Practice C 192/C 192M. Use the same curingtime when comparison between or among laboratories isdesired.7.3 Hardened Concrete:7.3.1 Select samples of hardened fiber-reinforced concr
39、etefrom structures in accordance with Practice C 823.7.3.2 Prepare and condition sawed beams in accordancewith Test Method C 42/C 42M. The sawed beams shall havedimensions 100 mm by 100 mm by 350 mm (4 in. by 4 in. by14 in.).8. Procedure8.1 Set the rate of platen or cross-head movement at 0.65 60.15
40、 mm/min (0.025 6 0.005 in/min.) before the beam isloaded (See Note 5).NOTE 5When necessary use the mechanical dial gage to establish thesetting for the rate of platen or crosshead movement.8.2 Turn the beam on its side with respect to its position asmolded and place on top of the steel plate to be l
41、oaded with thebeam (See Note 6). In the case that it is necessary to use sawedbeams, beams shall be turned with respect to their position ascast or molded so that the flexural tensile surface is a sawedsurface.NOTE 6The purpose of the stainless steel plate is to support the testbeam during the initi
42、al loading cycle to help control the expected high rateof deflection of the beam upon cracking.8.3 Place the plate and beam on the support apparatus sothat the steel plate is centered on the lower bearing blocks andthe concrete beam is centered on the steel plate. Adjust thedisplacement transducer(s
43、) according to the chosen apparatusfor obtaining net deflection.8.4 Ensure that the XY plotter or alternate data acquisitionsystem is activated and responding to signals from all load anddisplacement transducers.8.5 Begin loading the beam and steel plate combination atthe set rate and continue loadi
44、ng until reaching a deflection of0.20 mm (0.008 in.). If cracking has not occurred after reachinga deflection of 0.20 mm (0.008 in.) the test is invalid. Themaximum load is not to be used to calculate modulus of rupturein accordance with Test Method C78as this load includes loadcarried by the steel
45、plate as well as by the concrete beam.8.6 In anticipation of reloading the cracked beam only,remove the steel plate and center the cracked beam on thelower bearing blocks retaining the same orientation as duringthe initial loading test cycle. Adjust the displacement transduc-er(s) to lightly contact
46、 the beam in accordance with the chosenmethod for obtaining net deflection so that readings willimmediately be obtained upon beam reloading. Zero thedeflection recording device.8.7 Begin reloading at the specified rate used for the initialloading. Terminate the test at a deflection of 1.25 mm (0.050
47、in.) as measured from the beginning of reloading.8.8 Measure the beam and crack location as in Test MethodC78.C 1399 07a49. Calculation9.1 Calculate the average residual strength (ARS) for eachbeam to the nearest 0.01 MPa (2 psi) using the loads deter-mined at reloading curve deflections of 0.50, 0.
48、75, 1.00, and1.25 mm (0.020, 0.030, 0.040, and 0.050 in.) as follows:ARS 5 PA1 PB1 PC1 PD! /4! 3 k (1)where:k = L/bd2,mm2(in2)ARS = average residual strength, MPa (psi),PA+PB+PC+PD= sum of recorded loads at specified de-flections, N (lbf),L = span length, mm (in.),b = average width of beam, mm (in.)
49、, andd = average depth of beam, mm (in.).9.2 Calculate the mean ARS for each set of beams to thenearest 0.05 MPa (5 psi).10. Report10.1 The test report shall include the following information.If specific information is unknown at the time of the test thenthe word “UNKNOWN” shall be used.10.1.1 Concrete mixture proportions.10.1.2 Type and amount of fiber reinforcement.10.1.3 Test beam information including:10.1.3.1 beam identification labels,10.1.3.2 type of beam (molded or sawed),10.1.3.3 average width of beam to the nearest 1.0 mm (0.05in
