1、Designation: C 1550 08Standard Test Method forFlexural Toughness of Fiber Reinforced Concrete (UsingCentrally Loaded Round Panel)1This standard is issued under the fixed designation C 1550; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 expres
3、sed 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
4、of 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 limitation
6、s prior to use.2. Referenced Documents2.1 ASTM Standards:2C 31/C 31M Practice for Making and Curing Concrete TestSpecimens in the FieldC 125 Terminology Relating to Concrete and ConcreteAggregatesC 670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction Materials3.
7、Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology C 125.3.2 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 p
8、anel; 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 ordeflec
9、tion 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
10、under 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.
11、Theload 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 tough
12、ness 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 circum
13、ference.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 representedby the energy absorbed by the panel up to
14、 a specified centraldeflection. In this test method, the energy absorbed up to aspecified central deflection is taken to represent the ability of afiber-reinforced concrete to redistribute stress following crack-ing.1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Con
15、crete Aggregates and is the direct responsibility of SubcommitteeC09.42 on Fiber-Reinforced Concrete.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 2002. Last previous edition approved in 2005 as C 1550 05.2For referenced ASTM standards, visit the ASTM website,
16、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 this standard.Copyright ASTM International, 100 Barr Harbor Driv
17、e, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 distribution of fl
18、exural 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 absorbed up to
19、 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 intended application
20、 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 be required to
21、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 of central def
22、lectioncan 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 arises through t
23、he 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 nominal dimensions
24、 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 dimensions.NOT
25、E 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 long fibers are
26、 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 this test method
27、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 method are more
28、representative 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 actuatorto control th
29、e 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 used), andsupp
30、ort 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-backloop for automat
31、ically 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 centraldisplacement of
32、 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 reliable configurati
33、on 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-reinforced concrete p
34、anels 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 includes threes
35、ymmetrically 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 more than 0.5 mm
36、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 panel fragments
37、 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 shall comprise
38、 a steel transferplate with plan dimensions of approximately 40 3 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 pivot ball sh
39、all 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 points ina
40、manner that excludes extraneous deformations of the testingmachine and support fixture. This is achieved by one of two3Bernard, 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., C
41、ollis,A., and Bernard, E. S., “The M5 Motorway:An Educationin Quality Assurance for Fibre Reinforced Shotcrete,” Shotcrete: EngineeringDevelopments, Bernard (ed.), Swets fiber-reinforced concrete; flexure;post-crack behavior; toughnessFIG. 5 Integration of Area Under Load-Net Deflection Curve toObta
42、in Energy AbsorptionC1550086ANNEX(Mandatory Information)A1. DETERMINATION OF LOAD-TRAIN COMPLIANCEA1.1 The compliance of the load train is the differencebetween the apparent compliance of the specimen whendeformation of the load train is included and the true compli-ance of the specimen.CLT5 Capp2 C
43、spec(A1.1)where:CLT= the compliance of the load train,Capp= the apparent compliance of the specimen inclusiveof load train deformation,Cspec= the true compliance of the specimen.Compliance shall be measured in units of mm/kN. The termCspeccan be determined by dividing the load, P, to cause agiven ce
44、ntral deflection into the corresponding deflection,Dspec, measured so as to exclude deformations of the load trainand corrected for crushing of concrete. Hence,Cspec5Dspec/ P (A1.2)The term Cappis determined in a similar manner, but thecentral deflection, Dapp, arising from the load, P, shall includ
45、ethe 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 slope of a linefitted through the straight portion of the load-deflection recordprior to cracking is
46、 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 of the specimenrelative to the support points prior to cracking is the compli-ance of the specime
47、n, 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 of the center of the specimen is measured relative tothe supported portions of the specimen. Since
48、 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 supportsby means of a yoke (see Figs. A1.1 and A1.2, and Section 6).The yoke shall be loosely sup
49、ported 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 this is correctedthrough attention to the off-set in the load-deflection recordshown in Fig. A1.3. A plan view of a suggested test configu-ration for the measurement of load train compliance is shownin Fig. A1.4.FIG. A1.1 Suggested Method of Deflection Measurement toExclude Load-Train Deformations and Crushing of Concrete atthe Point of Loading Using a Linear Variable Deflect
