1、Designation: C 1550 05Standard 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 (e) 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 expre
3、ssed 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 as thestandard.1.4 This standard does no
5、t 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 Standard
6、s: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. Terminology3.1 DefinitionsFor definitions of terms used
7、 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 panel; this is a conditioned deflectionthat excludes ext
8、raneous 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 divided by the corresponding load.3.2.3 load train
9、those 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 under the load-deflection curve betweenthe onset of loa
10、ding 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. Theload is applied through a hemispherical-ended steel
11、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 ofthe fiber-reinforced concrete panel.5. Significa
12、nce 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 circumference.Such a test panel experiences bi-axial bending
13、in response to acentral point load and exhibits a mode of failure related to thein situ behavior of structures such as concrete slabs-on-grade,shotcrete tunnel linings, and shotcrete embankment stabiliza-tion linings. The post-crack performance of round panelssubject to a central point load can be r
14、epresented by the energyabsorbed by the panel up to a specified central deflection. Inthis test method, the energy absorbed up to a specified central1This test method is under the jurisdiction of ASTM Committee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC0
15、9.42 on Fiber-Reinforced Concrete.Current edition approved July 1, 2005. Published August 2005. Originallyapproved in 2002. Last previous edition approved in 2004 as C 1550-04.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. Fo
16、r 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 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.defl
17、ection is taken to represent the ability of a fiber-reinforcedconcrete to redistribute stress following cracking.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 af
18、ter cracking due to theunknown distribution 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
19、deflection isincreased. The energy 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 deflect
20、ionto specify depends on the intended 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
21、 such as railway tunnels that may be 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 ab
22、sorption up to intermediate values 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 con
23、sistency of thefailure mode that arises 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 sh
24、otcrete beam specimens.5.3 The nominal 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 prov
25、ided toaccount for actual measured 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 effec
26、ts if large aggregate particlesor long 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
27、post-crack behaviorexhibited in this 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 beh
28、avior in specimens tested by this method 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
29、the specimen or the loading actuatorto 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 incl
30、usive of load frame, load cell (if 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 mechanism
31、s lacking an electronic feed-backloop 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
32、loop in which the measured centraldisplacement 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
33、the loading apparatus.A more reliable 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
34、 stress thatoccurs in fiber-reinforced 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
35、consist of any configuration that includes 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 notdisp
36、lace in the radial direction by more 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 pivotss
37、hall not restrict rotation of the panel 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
38、betweenthe specimen and each pivot shall comprise 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 sha
39、ll be 20 62 mm. The diameter of the pivot 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
40、 the specimen relative to the support points ina 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, RILE
41、M, Vol 35,April 2002,pp. 156-164.4Hanke, S.A., Collis,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 Integratio
42、n of Area Under Load-Net Deflection Curve toObtain Energy AbsorptionC1550056ANNEX(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 t
43、he 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 inclusiveof load train deformation,Cspec= the true compliance of the specimen.Compliance shall be measured in units of mm/kN. The termCspeccan be determ
44、ined by dividing the load, P, to cause agiven central 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 deflecti
45、on, Dapp, 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 slope of a linefitted through the straight portion o
46、f 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 of the specimenrelative to the support points pri
47、or 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 of the center of the specimen is measured relative
48、 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 supportsby means of a yoke (see Figs. A1.1 and A1
49、.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 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 Poi
