ASTM C1609 C1609M-2007 Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam With Third-Point Loading).pdf

1、Designation: C 1609/C 1609M 07Standard Test Method forFlexural Performance of Fiber-Reinforced Concrete (UsingBeam With Third-Point Loading)1This standard is issued under the fixed designation C 1609/C 1609M; the number immediately following the designation indicates theyear of original adoption or,

2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method evaluates the flexural performance offiber-reinforced concret

3、e using parameters derived from theload-deflection curve obtained by testing a simply supportedbeam under third-point loading using a closed-loop, servo-controlled testing system.1.2 This test method provides for the determination offirst-peak and peak loads and the corresponding stressescalculated

4、by inserting them in the formula for modulus ofrupture given in Eq 1. It also requires determination of residualloads at specified deflections, and the corresponding residualstrengths calculated by inserting them in the formula formodulus of rupture given in Eq 1 (see Note 1). At the option ofthe sp

5、ecifier of tests, it provides for determination of specimentoughness based on the area under the load-deflection curve upto a prescribed deflection (see Note 2).NOTE 1Residual strength is not a true stress but an engineering stresscomputed using simple engineering bending theory for linear elasticma

6、terials and gross (uncracked) section properties.NOTE 2Specimen toughness expressed in terms of the area under theload-deflection curve is an indication of the energy absorption capabilityof the particular test specimen, and its magnitude depends directly on thegeometry of the test specimen and the

7、loading configuration.1.3 This test method utilizes two preferred specimen sizesof 100 by 100 by 350 mm 4 by 4 by 14 in. tested on a 300 mm12 in. span, or 150 by 150 by 500 mm 6 by 6 by 20 in.tested on a 450 mm 18 in. span. A specimen size differentfrom the two preferred specimen sizes is permissibl

8、e.1.4 UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. Thevalues stated in each system may not be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the two systems may result in non-conforma

9、nce with the 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

10、to use.2. Referenced Documents2.1 ASTM Standards:2C 31/C 31M Practice for Making and Curing Concrete TestSpecimens 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

11、 Loading)C 125 Terminology Relating to Concrete and ConcreteAggregatesC 172 Practice for Sampling Freshly Mixed ConcreteC 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the LaboratoryC 823 Practice for Examination and Sampling of HardenedConcrete in ConstructionsC 1140 Practice

12、for Preparing and Testing Specimens fromShotcrete Test Panels3. Terminology3.1 DefinitionsThe terms used in this test method aredefined in Terminology C 125.3.2 Definitions of Terms Specific to This Standard:3.2.1 end-point deflectionthe deflection value on the load-deflection curve equal to1150 of

13、the span length, or a largervalue as specified at the option of the specifier of tests.3.2.2 first-peak load, P1the load value at the first point onthe load-deflection curve where the slope is zero.3.2.3 first-peak deflection, d1the net deflection value onthe load-deflection curve at first-peak load

14、.3.2.4 first-peak strength f1the stress value obtained whenthe first-peak load is inserted in the formula for modulus ofrupture given in Eq 1.3.2.5 load-deflection curvethe plot of load versus netdeflection of a flexural beam specimen loaded to the end-pointdeflection.1This test method is under the

15、jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.42 on Fiber-Reinforced Concrete.Current edition approved Dec. 15, 2007. Published January 2008. Originallyapproved in 2005. Last previous edition approved in 2006 as C 1609/C 160

16、9M 06.2For 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 appears at the end of th

17、is standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.6 net deflectionthe deflection measured at mid-span ofa flexural beam specimen exclusive of any extraneous effectsdue to seating or twisting of the specimen on its suppor

18、ts ordeformation of the support and loading system.3.2.7 peak load, PPthe maximum load on the load-deflection curve.3.2.8 peak-load deflection, dPthe net deflection value onthe load-deflection curve at peak load.3.2.9 peak strength, fPthe stress value obtained when thepeak load is inserted in the fo

19、rmula for modulus of rupturegiven by Eq 1.3.2.10 Dnominal depth of the beam specimen in mm.NOTE 3To simplify nomenclature, the nominal beam depth is shownin units of mm for both the SI and inch-pound version of this test method.3.2.11 Lspan length or distance between the supports.3.2.12 residual loa

20、d, P600Dthe load value correspondingto a net deflection of L/600 for a beam of nominal depth D.3.2.13 residual load, P150Dthe load value correspondingto a net deflection of L/150 for a beam of nominal depth D.3.2.14 residual strength, f600Dthe stress value obtainedwhen the residual load P600Dis inse

21、rted in the formula formodulus of rupture given in Eq 1.3.2.15 residual strength, f150Dthe stress value obtainedwhen the residual load P150Dis inserted in the formula formodulus of rupture given in Eq 1.3.2.16 specimen toughness, T150Dtoughness of beamspecimen of nominal depth D at a net deflection

22、of L/150.4. Summary of Test Method4.1 Molded or sawn beam specimens having a squarecross-section of fiber-reinforced concrete are tested in flexureusing a third-point loading arrangement similar to that speci-fied in Test Method C78 but incorporating a closed-loop,servo-controlled testing system and

23、 roller supports that are freeto rotate on their axes. Load and net deflection are monitoredand recorded to an end-point deflection of at least1150 of thespan. Data are recorded and plotted by means of an X-Yplotter, or they are recorded digitally and subsequently used toplot a load-deflection curve

24、. Points termed first-peak, peak, andresidual loads at specified deflections are identified on thecurve, and are used to calculate flexural performance param-eters.5. Significance and Use5.1 The first-peak strength characterizes the flexural behav-ior of the fiber-reinforced concrete up to the onset

25、 of cracking,while residual strengths at specified deflections characterize theresidual capacity after cracking. Specimen toughness is ameasure of the energy absorption capacity of the test specimen.The appropriateness of each parameter depends on the natureof the proposed application and the level

26、of acceptable crack-ing and deflection serviceability. Fiber-reinforced concrete isinfluenced in different ways by the amount and type of fibers inthe concrete. In some cases, fibers may increase the residualload and toughness capacity at specified deflections whileproducing a first-peak strength eq

27、ual to or only slightly greaterthan the flexural strength of the concrete without fibers. Inother cases, fibers may significantly increase the first-peak andpeak strengths while affecting a relatively small increase inresidual load capacity and specimen toughness at specifieddeflections.5.2 The firs

28、t-peak strength, peak strength, and residualstrengths determined by this test method reflect the behavior offiber-reinforced concrete under static flexural loading. Theabsolute values of energy absorption obtained in this test are oflittle direct relevance to the performance of fiber-reinforcedconcr

29、ete structures since they depend directly on the size andshape of the specimen and the loading arrangement.5.3 The results of this test method may be used for com-paring the performance of various fiber-reinforced concretemixtures or in research and development work. They may alsobe used to monitor

30、concrete quality, to verify compliance withconstruction specifications, obtain flexural strength data onfiber-reinforced concrete members subject to pure bending, orto evaluate the quality of concrete in service.5.4 The results of this standard test method are dependenton the size of the specimen.NO

31、TE 4The results obtained using one size molded specimen may notcorrespond to the performance of larger or smaller molded specimens,concrete in large structural units, or specimens sawn from such units. Thisdifference may occur because the degree of preferential fiber alignmentbecomes more pronounced

32、 in molded specimens containing fibers that arerelatively long compared with the cross-sectional dimensions of the mold.Moreover, structural members of significantly different thickness experi-ence different maximum crack widths for a given mid-span deflection withthe result that fibers undergo diff

33、erent degrees of pull-out and extension.6. Apparatus6.1 Testing MachineThe testing machine shall be capableof servo-controlled operation where the net deflection of thecenter of the beam is measured and used to control the rate ofincrease of deflection. Testing machines that use stroke dis-placement

34、 control or load control are not suitable for estab-lishing the portion of the load-deflection curve immediatelyafter first-peak. The loading and specimen support system shallbe capable of applying third-point loading to the specimenwithout eccentricity or torque. The fixtures specified in TestMetho

35、d C78are suitable with the qualification that supportingrollers shall be able to rotate on their axes and shall not beplaced in grooves or have other restraints that prevent their freerotation.6.2 Deflection-Measuring EquipmentDevices such aselectronic transducers or electronic deflection gages shal

36、l belocated in a manner that ensures accurate determination of thenet deflection at the mid-span exclusive of the effects of seatingor twisting of the specimen on its supports. One acceptablearrangement employs a rectangular jig, which surrounds thespecimen and is clamped to it at mid-depth directly

37、 over thesupports (Figs. 1 and 2). Two electronic displacement trans-ducers or similar digital or analog devices mounted on the jigat mid-span, one on each side, measure deflection throughcontact with appropriate brackets attached to the specimen.The average of the measurements represents the net de

38、flection.6.3 Data Recording SystemAn X-Y plotter coupled di-rectly to electronic outputs of load and deflection is anacceptable means of obtaining the relationship between loadand net deflectionthat is, the load-deflection curve. A dataC 1609/C 1609M 072acquisition system capable of digitally record

39、ing and storingload and deflection data at a sampling frequency of at least 2.5Hz is an acceptable alternative. After a net deflection of L/600has been exceeded, it is permissible to decrease the dataacquisition sampling and recording frequency to 1 Hz.NOTE 5For X-Y plotters, accurate determination

40、of the area under theload-deflection curve and the loads corresponding to specified deflectionsis only possible when the scales chosen for load and deflection arereasonably large. A load scale chosen such that 25 mm 1 in. correspondsto a flexural stress of the order of 1 MPa 150 psi, or no more than

41、 20 %of the estimated first-peak strength, is recommended. A recommendeddeflection scale is to use 25 mm 1 in. to represent about 10 % of theend-point deflection of1150 of the span, which is 2 mm 0.08 in. for a 350by 100 by 100 mm 14 by 4 by 4 in. specimen size, and 3 mm 0.12 in.for a 500 by 150 by

42、150 mm 20 by 6 by 6 in. specimen size. When dataare digitally stored, the test parameters may be determined directly fromthe stored data or from a plot of the data. In the latter case, use a plot scalesimilar to that recommended for an X-Y plotter.FIG. 1 Arrangement to Obtain Net Deflection by Using

43、 Two Transducers Mounted on Rectangular Jig Clamped to Specimen DirectlyAbove SupportsFIG. 2 Arrangement to Obtain Net Deflection by Using Two Transducers Mounted on Jig Secured to Specimen Directly Above SupportsC 1609/C 1609M 0737. Sampling, Test Specimens, and Test Units7.1 General RequirementsTh

44、e nominal maximum size ofaggregate and cross-sectional dimensions of test specimensshall be in accordance with Practice C 31/C 31M or PracticeC 192/C 192M when using molded specimens, or in accor-dance with Test Method C 42/C 42M when using sawn speci-mens, provided that the following requirements a

45、re satisfied:7.1.1 The length of test specimens shall be at least 50 mm 2in. greater than three times the depth, and in any case not lessthan 350 mm 14 in. The length of the test specimen shall notbe more than two times the depth greater than the span.7.1.2 The tolerances on the cross-section of the

46、 test speci-mens shall be within 6 2 %. The test specimens shall have asquare cross-section within these tolerances.7.1.3 The width and depth of test specimens shall be at leastthree times the maximum fiber length.7.1.4 When the specimen size is not large enough to meet allthe requirements of 7.1-7.

47、1.3, specimens of square cross-section large enough to meet the requirements shall be used.The three times maximum fiber length requirement for widthand depth may be waived at the option of the specifier of teststo permit specimens with a width and depth of 150 mm 6 in.when using fibers of length 50

48、 to 75 mm 2 to 3 in.NOTE 6The results of tests on beams with relatively stiff fibers, suchas steel fibers, longer than one-third the width and depth of the beam maynot be comparable with test results of similar-sized beams with fibersshorter than one-third the width and depth because of preferential

49、 fiberalignment, and different size beams may not be comparable because ofsize effects. The degree of preferential fiber alignment may be less forfibers that are flexible enough to be bent by contact with aggregateparticles or mold surfaces than for rigid fibers that remain straight duringmixing and specimen preparation.7.2 Freshly Mixed ConcreteObtain samples of freshlymixed fiber-reinforced concrete for the preparation of testspecimens in accordance with Practice C 172.7.2.1 Mold specimens in accordance with Practic