Designation: C1609/C1609M − 12Standard Test Method forFlexural Performance of Fiber-Reinforced Concrete (UsingBeam With Third-Point Loading)1This standard is issued under the fixed designation C1609/C1609M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, 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*1.1 This test method evaluates the flexural performance offiber-reinforced concrete 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 by inserting them in the formula for modulus ofrupture given in Eq 1. It also requires determination of residualloads at specified deflections, the corresponding residualstrengths calculated by inserting them in the formula formodulus of rupture given in Eq 1 (see Note 1). It provides fordetermination of specimen toughness based on the area underthe load-deflection curve up to a prescribed deflection (seeNote 2) and the corresponding equivalent flexural strengthratio.NOTE 1—Residual strength is not a true stress but an engineering stresscomputed using simple engineering bending theory for linear elasticmaterials and gross (uncracked) section properties.NOTE 2—Specimen 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 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 mm[12 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 permissible.1.4 Units—The 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-conformance 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 to use.2. Referenced Documents2.1 ASTM Standards:2C31/C31M Practice for Making and Curing Concrete TestSpecimens in the FieldC42/C42M 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)C125 Terminology Relating to Concrete and Concrete Ag-gregatesC172 Practice for Sampling Freshly Mixed ConcreteC192/C192M Practice for Making and Curing Concrete TestSpecimens in the LaboratoryC823 Practice for Examination and Sampling of HardenedConcrete in ConstructionsC1140 Practice for Preparing and Testing Specimens fromShotcrete Test Panels3. Terminology3.1 Definitions—The terms used in this test method aredefined in Terminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 end-point deflection, n—the deflection value on theload-deflection curve equal to1⁄150 of the span length, or alarger value as specified at the option of the specifier of tests.3.2.2 first-peak load, P1,n—the load value at the first pointon the load-deflection curve where the slope is zero.3.2.3 first-peak deflection, δ1,n—the net deflection value onthe load-deflection curve at first-peak load.1This 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 edition approved Dec. 1, 2012. Published January 2013. Originallyapproved in 2005. Last previous edition approved in 2010 as C1609/C1609M – 10.DOI: 10.1520/C1609_C1609M-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.4 first-peak strength f1,n—the stress value obtainedwhen the first-peak load is inserted in the formula for modulusof rupture given in Eq 1.3.2.5 load-deflection curve, n—the plot of load versus netdeflection of a flexural beam specimen loaded to the end-pointdeflection.3.2.6 net deflection, n—the deflection measured at mid-spanof a flexural beam specimen exclusive of any extraneouseffects due to seating or twisting of the specimen on itssupports or deformation of the support and loading system.3.2.7 peak load, PP,n—the maximum load on the load-deflection curve.3.2.8 peak-load deflection, δP,n—the net deflection valueon the load-deflection curve at peak load.3.2.9 peak strength, fP,n—the stress value obtained whenthe peak load is inserted in the formula for modulus of rupturegiven by Eq 1.3.2.10 D—nominal depth of the beam specimen in mm.NOTE 3—To 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 L—span length or distance between the supports.3.2.12 residual load, P600D,n—the load value correspondingto a net deflection of L/600 for a beam of nominal depth D.3.2.13 residual load, P150D,n—the load value correspondingto a net deflection of L/150 for a beam of nominal depth D.3.2.14 residual strength, f600D,n—the stress value obtainedwhen the residual load P600Dis inserted in the formula formodulus of rupture given in Eq 1.3.2.15 residual strength, f150D,n—the stress value obtainedwhen the residual load P150Dis inserted in the formula formodulus of rupture given in Eq 1.3.2.16 specimen toughness, T150D,n—toughness of beamspecimen of nominal depth D at a net deflection of L/150.3.2.17 equivalent flexural strength ratio, RT, 150D,n—the valueobtained when the specimen toughness T150Dis inserted in Eq 3.NOTE 4—The equivalent flexural strength ratio is calculated as the ratioof the weighted equivalent load up to a net deflection of L/150 over thefirst-peak load multiplied by 100. The RT, 150150value is equivalent to the Re,3value defined in the Technical Report No. 34 of the Concrete Society.34. 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 roller supports that are freeto rotate on their axes. Load and net deflection are monitoredand recorded to an end-point deflection of at least1⁄150 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. 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 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 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 equal 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 first-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-reinforcedconcrete 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 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.NOTE 5—The 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 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 different degrees of pull-out and extension.6. Apparatus6.1 Testing Machine—The 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 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 TestMethod C78 are suitable with the qualification that supporting3“Concrete Industrial Ground Floors—A Guide to Design and Construction,”Technical Report 34, 3rdedition, Concrete Society, Slough, United Kingdom, 2003.C1609/C1609M − 122rollers 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 Equipment—Devices such aselectronic transducers or electronic deflection gages shall 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 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 deflection.6.3 Data Recording System—An X-Y plotter coupled di-rectly to electronic outputs of load and deflection is anacceptable means of obtaining the relationship between loadand net deflection—that is, the load-deflection curve. A dataacquisition system capable of digitally recording and storingload and deflection data at a sampling frequency of at least 2.5Hz is an acceptable alternative. After a net deflection of L/900has been exceeded, it is permissible to decrease the dataacquisition sampling and recording frequency to at least 2 Hz.This applies regardless of the rate of deflection used to load thespecimen.NOTE 6—For X-Y plotters, accurate determination 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 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 of1⁄150 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 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.7. Sampling, Test Specimens, and Test Units7.1 General Requirements—The nominal maximum size ofaggregate and cross-sectional dimensions of test specimensshall be in accordance with Practice C31/C31M or PracticeC192/C192M when using molded specimens, or in accordancewith Test Method C42/C42M when using sawn specimens,provided that the following requirements are 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 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 – 7.1.3, 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 to 75 mm [2 to 3 in.].NOTE 7—The 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 fiberalignment, and different size beams may not be comparable because ofsize effects. The degree of preferent