1、Designation: C1550 12aStandard Test Method forFlexural Toughness of Fiber Reinforced Concrete (UsingCentrally Loaded Round Panel)1This standard is issued under the fixed designation C1550; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of flexuraltoughness of fiber-reinforced concrete express
3、ed as energyabsorption in the post-crack range using a round panel sup-ported on three symmetrically arranged pivots and subjected toa central point load. The performance of specimens tested bythis method is quantified in terms of the energy absorbedbetween the onset of loading and selected values o
4、f centraldeflection.1.2 This test method provides for the scaling of resultswhenever specimens do not comply with the target thicknessand diameter, as long as dimensions do not fall outside of givenlimits.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement
5、are included in thisstandard.1.4 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
6、 prior to use.2. Referenced Documents2.1 ASTM Standards:2C31/C31M Practice for Making and Curing Concrete TestSpecimens in the FieldC125 Terminology Relating to Concrete and Concrete Ag-gregatesC670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction Materials3. Ter
7、minology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology C125.3.2 Definitions of Terms Specific to This Standard:3.2.1 central deflectionthe net deflection at the center ofthe panel measured relative to a plane defined by the threepivots used to support the panel
8、; this is a conditioned deflectionthat excludes extraneous deformations of the load train andlocal crushing of the panel at the point of load application andpoints of support.3.2.2 compliancea measure of the tendency of a structureto deflect under load, found as the inverse of stiffness ordeflection
9、 divided by the corresponding load.3.2.3 load trainthose parts of a testing machine thatexperience load and undergo straining during a mechanicaltest, including the actuator, frame, support fixtures, load cell,and specimen.3.2.4 toughnessthe energy absorbed by the specimenequivalent to the area unde
10、r the load-deflection curve betweenthe onset of loading and a specified central deflection.4. Summary of Test Method4.1 Molded round panels of cast fiber-reinforced concrete orfiber-reinforced shotcrete are subjected to a central point loadwhile supported on three symmetrically arranged pivots. Thel
11、oad is applied through a hemispherical-ended steel pistonadvanced at a prescribed rate of displacement. Load anddeflection are recorded simultaneously up to a specified centraldeflection. The energy absorbed by the panel up to a specifiedcentral deflection is representative of the flexural toughness
12、 ofthe fiber-reinforced concrete panel.5. Significance and Use5.1 The post-crack behavior of plate-like, fiber-reinforcedconcrete structural members is well represented by a centrallyloaded round panel test specimen that is simply supported onthree pivots symmetrically arranged around its circumfere
13、nce.Such a test panel experiences bi-axial bending in response to acentral point load and exhibits a mode of failure related to thein situ behavior of structures. The post-crack performance ofround panels subject to a central point load can be represented1This test method is under the jurisdiction o
14、f ASTM Committee C09 onConcrete and Concrete Aggregatesand is the direct responsibility of SubcommitteeC09.42 on Fiber-Reinforced Concrete.Current edition approved Dec. 1, 2012. Published December 2012. Originallyapproved in 2002. Last previous edition approved in 2012 as C155012. DOI:10.1520/C1550-
15、12a.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.*A Summary of Changes section appears at the end of this
16、standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1by the energy absorbed by the panel up to a specified centraldeflection. In this test method, the energy absorbed up to aspecified central deflection is taken to represent the ab
17、ility of afiber-reinforced concrete to redistribute stress following crack-ing.NOTE 1The use of three pivoted point supports in the test configura-tion results in determinate out-of-plane reactions prior to cracking,however the support reactions are indeterminate after cracking due to theunknown dis
18、tribution of flexural resistance along each crack. There is alsoa change in the load resistance mechanism in the specimen as the testproceeds, starting with predominantly flexural resistance and progressingto tensile membrane action around the center as the imposed deflection isincreased. The energy
19、 absorbed up to a specified central deflection isrelated to the toughness of the material but is specific to this specimenconfiguration because it is also determined by the support conditions andsize of the specimen. Selection of the most appropriate central deflectionto specify depends on the inten
20、ded application for the material.The energyabsorbed up to 5 mm central deflection is applicable to situations in whichthe material is required to hold cracks tightly closed at low levels ofdeformation. Examples include final linings in underground civil struc-tures such as railway tunnels that may b
21、e required to remain water-tight.The energy absorbed up to 40 mm is more applicable to situations in thatthe material is expected to suffer severe deformation in situ (for example,shotcrete linings in mine tunnels and temporary linings in swellingground). Energy absorption up to intermediate values
22、of central deflectioncan be specified in situations requiring performance at intermediate levelsof deformation.5.2 The motivation for use of a round panel with threesupports is based on the within-batch repeatability found inlaboratory3and field experience.4The consistency of thefailure mode that ar
23、ises through the use of three symmetricallyarranged support pivots results in low within-batch variabilityin the energy absorbed by a set of panels up to a specifiedcentral deflection. The use of round panels also eliminates thesawing that is required to prepare shotcrete beam specimens.5.3 The nomi
24、nal dimensions of the panel are 75 mm inthickness and 800 mm in diameter. Thickness has been shownto strongly influence panel performance in this test, whilevariations in diameter have been shown to exert a minorinfluence on performance.5Correction factors are provided toaccount for actual measured
25、dimensions.NOTE 2The target dimensions of the panel specimen used in this testare held constant regardless of the characteristics of aggregate and fibersused in the concrete comprising the specimen. Post-crack performancemay be influenced by size and boundary effects if large aggregate particlesor l
26、ong fibers are used in the concrete. These influences are acknowledgedand accepted in this test method because issues of size effect and fiberalignment arise in actual structures and no single test specimen cansuitably model structures of all sizes. Differences in post-crack behaviorexhibited in thi
27、s test method can be expected relative to cast fiber-reinforced concrete members thicker than 100 mm. Because fiber align-ment is pronounced in structures produced by shotcreting, and themaximum aggregate size in shotcrete mixtures is typically 10 mm,post-crack behavior in specimens tested by this m
28、ethod are morerepresentative of in situ behavior when they are produced by sprayingrather than casting concrete.6. Apparatus6.1 Testing MachineA servo-controlled testing machineincorporating an electronic feed-back loop that uses the mea-sured deflection of either the specimen or the loading actuato
29、rto control the motion of the actuator shall be used to producea controlled and constant rate of increase of deflection of thespecimen without the intervention of an operator. To avoidunstable behavior after cracking, the system stiffness of thetesting machine inclusive of load frame, load cell (if
30、used), andsupport fixture shall exceed that of the specimen. The systemstiffness of the testing machine can be determined in accor-dance with the procedure described in Annex A1. Load-controlled test machines incorporating one-way hydraulicvalves or screw mechanisms lacking an electronic feed-backlo
31、op for automatically controlling the rate of increase indisplacement shall not be used. The load-sensing device shallhave a resolution sufficient to record load to 650 N.NOTE 3Although it is commonly believed that servo-controlledsystems, incorporating a feed-back loop in which the measured centrald
32、isplacement of the specimen is used to control the motion of the actuator,are capable of overcoming the disadvantages of a structurally complianttesting machine, this will depend on the speed and sensitivity of thefeed-back loop and the mechanical response rate of the loading apparatus.A more reliab
33、le configuration comprises a servo-controlled actuator inwhich the measured displacement of the actuator is used in the feed-backloop to control the motion of the actuator combined with a high load trainstiffness. Experience has indicated that the redistribution of stress thatoccurs in fiber-reinfor
34、ced concrete panels following cracking of theconcrete matrix generally results in stable post-crack behavior provided atesting machine complying with the requirements of this section is used.6.2 Support FixtureThe fixture supporting the panel dur-ing testing shall consist of any configuration that i
35、ncludes threesymmetrically arranged pivot points on a pitch circle diameterof 750 mm. The supports shall be capable of supporting a loadof up to 100 kN applied vertically at the center of the specimen.The supports shall be sufficiently rigid so that they do notdisplace in the radial direction by mor
36、e than 0.5 mm betweenthe onset of loading and 40 mm central deflection for a testinvolving a specimen displaying a peak load capacity of 100kN. The three supports must also not translate by more than 0.5mm in the circumferential direction during a test. The pivotsshall not restrict rotation of the p
37、anel fragments after cracking.The support fixture shall be configured so that the specimendoes not come into contact with any portion of the supportfixture apart from the three pivots during a test. A photographof a suggested design is shown in Fig. 1. The contact betweenthe specimen and each pivot
38、shall comprise a steel transferplate with plan dimensions of approximately 40 50 mm witha spherical seat of about 4 mm depth machined into one surfaceto accept a ball pivot (see Fig. 2). The distance between thesurface of the panel and the center of the pivot shall be 20 62 mm. The diameter of the p
39、ivot ball shall be 16 6 2 mm.Grease is permitted to reduce friction in the seat of each pivot,but rollers or grease are not permitted to reduce frictionbetween the transfer plates and specimen.6.3 Deflection Measuring EquipmentDetermine the cen-tral deflection of the specimen relative to the support
40、 points in3Bernard, E. S. “Correlations in the Behaviour of Fibre Reinforced ShotcreteBeam and Panel Specimens,” Materials and Structures , RILEM, Vol 35, pp.156-164, April 2002.4Hanke, S.A., Collis,A., and Bernard, E. S., “The M5 Motorway:An Educationin Quality Assurance for Fibre Reinforced Shotcr
41、ete,” Shotcrete: EngineeringDevelopments, Bernard (ed.), Swets fiber-reinforced concrete; flexure;post-crack behavior; toughnessANNEX(Mandatory Information)A1. DETERMINATION OF LOAD-TRAIN COMPLIANCEA1.1 The compliance of the load train is the differencebetween the apparent compliance of the specimen
42、 whendeformation of the load train is included and the true compli-ance of the specimen.CLT5 Capp2 Cspec(A1.1)where:CLT= the compliance of the load train,Capp= the apparent compliance of the specimen inclusive ofload train deformation,Cspec= the true compliance of the specimen.Compliance shall be me
43、asured in units of mm/kN. The termCspeccan be determined by dividing the load, P, to cause agiven central deflection into the corresponding deflection,spec, measured so as to exclude deformations of the load trainand corrected for crushing of concrete. Hence,Cspec5 spec/P (A1.2)The term Cappis deter
44、mined in a similar manner, but thecentral deflection, app, arising from the load, P, shall includethe deformation of the load train.The use of a large number of data points to determine thecompliances Cappand Cspecis more accurate than the use of asingle pair of points. Hence, the inverse of the slo
45、pe of a linefitted through the straight portion of the load-deflection recordprior to cracking is the apparent compliance of the specimenand load train, Capp. The inverse of the slope of a line fittedthrough the straight portion of the load-deflection recordobtained by measurement of the deflection
46、of the specimenrelative to the support points prior to cracking is the compli-ance of the specimen, Cspec.A1.2 The deflection of a specimen exclusive of load-traindeformation is measured by applying displacement transducersdirectly to the surface of the specimen during a test so that thedeflection o
47、f the center of the specimen is measured relative tothe supported portions of the specimen. Since local crushing ofthe surface of the specimen is likely to occur under the loadpoint, it is usually necessary to measure deflection at the centeron the tensile face of the specimen relative to the pivot
48、supportsby means of a yoke (see Figs. A1.1 and A1.2, and Section 6).The yoke shall be loosely supported at the pivot supported toallow for a slight movement of these during deformation of thespecimen. A small extraneous deformation can arise throughcrushing of concrete at the transfer plates, but th
49、is is correctedTABLE 1 Minimum and Maximum Values of Energy Absorption inC1550 Round Panel SpecimensDeflection Minimum Energy, J Maximum Energy, J5 mm 61 13610 mm 121 20020 mm 195 34340 mm 236 473TABLE 2 Single-Operator Indexes of PrecisionParameter(1)Single-OperatorCoefficientof VariationA(2)AcceptableDifferencebetweenTwo IndividualTests(Percent ofTheir Average)A(3)Peak load 6.2 % 17 %Energy Absorption 10.1 % 28 %AThese numbers represent, respectively, the (1s%) and (d2s%) limits as describedin Practice C670.TABLE 3 Multilaboratory Indexes of PrecisionParameter(1)Multi
