aci_measurement of properties of fiber reinforced concrete

ACI 544.2R-89 (Reapproved 2009)

Measurement of Properties of Fiber Reinforced Concrete

Reported by ACI Committee 544

Shuaib H. AhmadM. ArockiasamyP. N. BalaguruClaire G. Ball*Hiram P. Ball, Jr.Gordon B. BatsonArnon BenturRobert J. CraigMarvin E. Criswell*Sidney FreedmanRichard E. GalerMelvyn A. GalinatV. S. Gopalaratnam*Antonio Jose GuerraLloyd E. HackmanM. Nadim HassounCharles H. Henager, Sr.*

Surendra P. Shah*Chairman

George C. HoffNorman M. HydukRoop L. JindalIver L. JohnsonColin D. Johnston*Charles W. Josifek*David R. Lankard*Brij M. MagoHenry N. Marsh, Jr.Assir MelamedNicholas C. MitchellHenry J. Molloy*D. R. MorganA. E. Naaman*Stanley L. PaulSeth L. PearlmanV. Ramakrishnan*D. V. Reddy

James I. Daniel*Secretary

This report outlines existing procedures for specimen preparation ingeneral and discusses testing, workability, flexural strength, tough-ness, and energy absorption. Newly developed test methods are pre-sented for the first time for impact strength and flexural toughness.The applicability of the following tests to fiber reinforced concrete(FRC) are reviewed: air content, yield, unit weight, compressivestrength, splitting tensile strength, freeze-thaw resistance, shrinkage,creep, modulus of elasticity, cavitation, erosion, and abrasion resis-tance.

Keywords: abrasion tests; cavitation; compression tests; cracking (fracturing);creep properties; energy absorption; erosion; fatigue (materials); fiber rein-forced concretes; flexural strength: freeze-thaw durability; impact tests; modu-lus of elasticity; shrinkage; splitting tensile strength; tests; toughness; work-ability.

CONTENTSIntroductionWorkabilityAir content, yield, and unit weightSpecimen preparationCompressive strengthFlexural strength

Ralph C. RobinsonE. K. Schrader*Morris SchupackShan SomayajiJ. D. SpeakmanR. N. Swamy*Peter C. Tatnall†B. L. TilsenGeorge J. Venta*Gary L. Vondran*Methi WecharatanaGilbert R. WilliamsonC. K. WilsonRonald E. WitthohmGeorge Y. WuRobert C. ZellersRonald F. Zollo*

ToughnessFlexural fatigue enduranceSplitting tensile strengthImpact resistanceFreeze-thaw resistanceLength change (shrinkage)Resistance to plastic shrinkage crackingCreepModulus of elasticity and Poisson’s ratioCavitation, erosion, and abrasion resistanceReporting of test dataRecommended references

INTRODUCTIONThis report applies to conventionally mixed and

placed fiber reinforced concrete (FRC) or fiber rein-forced shotcrete (FRS) using steel, glass, polymeric, andnatural fibers. It does not relate to thin glass fiber rein-forced cement or mortar products produced by thespray-up process. The Prestressed Concrete Institute, 1

ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in designing, plan-ning, executing, or inspecting construction and in preparingspecifications. Reference to these documents shall not be madein the Project Documents. If items found in these documentsare desired to be part of the Project Documents they shouldbe phrased in mandatory language and incorporated into theProject Documents.

*Members of the subcommittee that drafted this report.†Chairman of the subcommittee that drafted this report.This report supercedes ACI 544.2R-78 (Revised 1983). The revision was ex-

tensive. Existing sections were expanded and new sections were added. The or-der of presentation has been rearranged and references were provided.

Copyright © 1988, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or

by any means, including the making of copies by any photo process, or by anyelectronic or mechanical device, printed, written, or oral, or recording for soundor visual reproduction or for use in any knowledge or retrieval system or de-vice, unless permission in writing is obtained from the copyright proprietors.

544.2R-1

544.2R-2 MANUAL OF CONCRETE PRACTICE

Fig. 1-Slump versus inverted cone time10

Glassfibre Reinforced Cement Association,2 and ASTMhave prepared recommendations for test methods forthese spray-up materials.

The use of fiber reinforced concrete (FRC) haspassed from experimental small-scale applications toroutine factory and field applications involving theplacement of many hundreds of thousands of cubicyards annually throughout the world. This has createda need to review existing test methods and develop newmethods, where necessary, for determining the proper-ties of FRC. These methods are presented in an effortto standardize procedures and equipment so that testresults from different sources can be compared effec-tively. While it is recognized that the use of proceduresand equipment other than those discussed in this reportmay be employed because of past practices, availabilityof equipment, etc., use of nonstandard tests does notpromote the development or broadening of the database needed to quantify consistently properties of thevarious forms of FRC. To date, some progress onstandardization of test methods has been made inNorth America by ASTM and similar organizationsoutside North America, but greater efforts are needed,as is indicated in this report.

Although most of the test methods described in thisreport were developed initially for steel fiber reinforcedconcrete, they are applicable to concretes reinforcedwith glass, polymeric, and natural fibers, except whenotherwise noted.

The test methods described in this report may insome cases lead to difficulties or problems in obtaining

meaningful results. In these instances, Committee 544welcomes information on the problems and any modi-fication of equipment or procedures that provides moremeaningful results. This is of particular interest wheretests developed initially for steel FRC are used to mea-sure properties of concretes containing other fibers,such as glass, polymeric, or natural fibers.

WORKABILITYThe workability of freshly mixed concrete is a mea-

sure of its ability to be mixed, handled, transported,and, most importantly, placed and consolidated with aminimal loss of homogeneity and minimal entrappedair. Several tests are available to assess one or more ofthese characteristics.

Slump test (ASTM C 143)The slump test is a common, convenient, and inex-

pensive test, but it may not be a good indicator ofworkability for FRC. However, once it has been estab-lished that a particular FRC mixture has satisfactoryhandling and placing characteristics at a given slump,the slump test may be used as a quality control test tomonitor the FRC consistency from batch to batch.

Time of flow through inverted slump cone test(ASTM C 995)

This test has been developed specifically to measurethe workability of FRC.3 It effectively measures themobility or fluidity of the concrete under internal vi-bration. The test is not suitable for flowable mixturesof FRC, such as produced using high-range water-re-ducing admixtures, because the concrete tends to runthrough the cone without vibration. The slump test isused for monitoring the consistency of these concretes.

Fig. 1 shows typical results of this test for conven-tional and FRC mixtures in relation to slump. Even atvery low slump, FRC mixtures respond well to vibra-tion. The flattening of the FRC curve above 2 or 3 in.(50 or 75 mm) slump indicates that for these mixturesthere is no improvement in workability as slumps in-crease beyond about 2 in. (50 mm). Fig. 2 shows a sim-ilar curvilinear relationship between the slump ob-tained under static test conditions and the time of flowobtained with vibration. It also shows a linear relation-ship illustrating direct proportionality between invertedcone time and Vebe time. This suggests that both ofthese vibration-type tests measure essentially the samecharacteristic of the freshly mixed concrete. The exactnature of the relationships of Fig. 1 and 2 will varyfrom one concrete to another depending on aggregatemaximum size and gradation, fiber concentration, typeand aspect ratio, and air content.

The inverted cone test can be used to compare FRCto conventional mixtures with similar slump values. Forexample, at a 2 in. (50 mm) slump, a 3/8 in. (10 mm)aggregate FRC mixture has substantially less flow timethan a 3/4 in. (19 mm) aggegate mixture at the sameslump (Fig. 1). This demonstrates that although theslumps of these two mixtures are similar, the workabil-

PROPERTIES OF FIBER REINFORCED CONCRETE 544.2R-3

ity of the FRC mixture was much better. The advan-tage of the inverted slump cone test over the slump testis that it takes into account the mobility of concrete,which comes about because of vibration.

Vebe testThe Vebe consistometer described in the British

Standards Institution standard BS 1881, “Methods ofTesting Concrete, Part 2,” measures the behavior ofconcrete subjected to external vibration and is accept-able for determining the workability of concrete placedusing vibration, including FRC. It effectively evaluatesthe mobility of FRC, that is, its ability to flow undervibration, and helps to assess the ease with which en-trapped air can be expelled. The Vebe test is not asconvenient for field use as either the slump or invertedcone test because of the size and weight of the equip-ment.

AIR CONTENT, YIELD, AND UNIT WEIGHTStandard ASTM air content test equipment and pro-

cedures for conventional concrete can be used for de-termining the air content, yield, and unit weight ofFRC (ASTM C 138, C 173, and C 231). The concretesamples should be consolidated using external or inter-nal vibration as permited by ASTM C 31 and C 192,and not by rodding. Rodding may be used when a highflow consistency has been produced by the use of high-range water-reducing admixtures.

SPECIMEN PREPARATIONIn general, procedures outlined in ASTM C 31, C 42,

C 192, and C 1018 should be followed for specimenpreparation. Additional guidance for preparing fiberreinforced shotcrete specimens is available in ACI506.2-77 (Revised 1983). Test specimens should be pre-pared using external vibration whenever possible.Internal vibration is not desirable and rodding is notacceptable, as these methods of consolidation may pro-duce preferential fiber alignment and nonuniform dis-tribution of fibers. Although external vibration mayproduce some alignment of fibers, the amount ofalignment produced in the short duration vibration re-quired for consolidation of test specimens is of negli-gible influence.

The method, frequency, amplitude, and time of vi-bration should be recorded. Test specimens having adepth of 3 in. (75 mm) or less should be cast in a singlelayer to avoid fiber orientation and fiber-free planes.Two layers should be used for specimens of depthgreater than 3 in. (75 mm) with each layer being vi-brated. Care should be taken to avoid placing the con-crete in a manner that produces a lack of fiber conti-nuity between successive placements. The preferredplacement method is to use a wide shovel or scoop andplace each layer of concrete uniformly along the lengthof the mold. Any preferential fiber alignment by themold surfaces can influence test results, particularly forsmall cross sections with long fibers. Generally, thesmallest specimen dimension should be at least three

Fig. 2-Relationship between slump, Vebe time, andinverted cone time3

times the larger of the fiber length and the maximumaggregate size. Recommendations for selecting speci-men size and preparing test specimens for flexuraltoughness tests are given in ASTM C 1018.

COMPRESSIVE STRENGTHASTM compressive strength equipment and proce-

dures (ASTM C 31, C 39, and C 192) used for conven-tional concrete can be used for FRC. The cylindersshould be 6 x 12 in. (150 x 300 mm) in size and shouldbe made using external vibration or a 1 in. (25 mm)nominal width internal vibrator. External vibration ispreferred since an internal vibrator may adversely in-fluence random fiber distribution and alignment.

The presence of fibers alters the mode of failure ofcylinders by making the concrete less brittle. Signifi-cant post-peak strength is retained with increasing de-formation beyond the maximum load. Fibers usuallyhave only a minor effect on compressive strength,slightly increasing or decreasing the test result. Sincesmaller cylinders give higher strengths for conventionalconcrete and promote preferential fiber alignment inFRC, small cylinders with long fibers may give unreal-istically high strengths. Cubes may also be used forcompressive strength tests, but few reference data areavailable for such specimens and the relationship be-tween cube strength and cylinder strength has not beendetermined for FRC.

FLEXURAL STRENGTHThe flexural strength of FRC may be determined un-

der third-point loading using ASTM C 78 or C 1018, orby center-point loading using ASTM C 293. Third-point loading is the preferred technique. If only maxi-mum flexural strength is of interest, ASTM C 78 orC 293 can be used. Maximum flexural strength is cal-culated at the section of maximum moment corre-


Fig. 3-Flexural strength-Calculated in accordancewith ASTM C 78 or C 293 using the maximum load

sponding to the peak fiber stress in tension based on theassumption of elastic behavior, as shown in Fig. 3. Iftoughness or load-deflection behavior is also of inter-est, ASTM C 1018 can be used. However, results ob-tained in load-controlled testing according to ASTMC 78 may differ from those obtained using the deflec-tion-controlled procedures of ASTM C 1018.4

At least three specimens should be made for each testaccording to the “Specimen Preparation” section ofthis report and ASTM C 1018. For thick sections,specimen width and depth should equal or exceed threetimes both the fiber length and the nominal dimensionof the maximum size aggregate. When the applicationfor the FRC involves a thickness less than this, e.g.,overlays, specimens with a depth equal to the actualsection thickness should be prepared. These should betested as cast, rather than turned 90 deg as is requiredfor standard-size beams, to evaluate the effects of pref-erential fiber alignment to be representative of the FRCin practice.

When it is possible to meet the width and depth re-quirements of three times the fiber length and aggre-gate size, a set of specimens with a preferred size of 4 x4 x 14 in. (100 x 100 x 350 mm) should be made andtested with third-point loading to allow comparison ofresults with a large base of available data from otherprojects that have used this as the standard test speci-men. Otherwise, the size of specimens for thick sec-tions should conform to the requirements of ASTMC 1018. If the width or depth of a specimen is less thanthree times the fiber length, preferential fiber align-ment tends to increase the measured flexural strength.This increase is representative only when a similar pref-erential fiber alignment increase can be expected for theFRC in use.

The relationship between flexural strength and directtensile strength has not been determined for FRC.

TOUGHNESSToughness is a measure of the energy absorption ca-

pacity of a material and is used to characterize the ma-terial’s ability to resist fracture when subjected to staticstrains or to dynamic or impact loads. The difficultiesof conducting direct tension tests on FRC prevent theiruse in evaluating toughness. Hence, the simpler flex-ural test is recommended for determining the toughnessof FRC. In addition to being simpler, the flexural test

simulates the loading conditions for many practical ap-plications of FRC.

The flexural toughness and first-crack strength canbe evaluated under third-point loading using specimensmeeting the requirements for thick sections or for thinsections outlined in ASTM C 1018. Specimens shouldbe prepared and tested according to ASTM C 1018 toestablish the load-deflection curve. The flexuralstrength may also be determined from the maximumload reading in this test as an alternative to evaluationin accordance with ASTM C 78.

Energy absorbed by the specimen is represented bythe area under the complete load-deflection (P-d) curve.The P-d curve has been observed to depend on (a) thespecimen size (depth, span, and width); (b) the loadingconfiguration (midpoint versus third-point loading); (c)type of control (load, load-point deflection, cross-headdisplacement, etc.); and (d) the loading rate.5,6

To minimize at least some of these effects, normali-zation of the energy absorption capacity is necessary.This can be accomplished by dividing the energy ab-sorbed by the FRC beam by that absorbed by an un-reinforced beam of identical size and matrix composi-tion, tested under similar conditions. The resultantnondimensional index It (Fig. 4) represents the relativeimprovement in the energy absorption capacity due tothe inclusion of the fibers.7 It is an index for compar-ing the relative energy absorption of different fibermixes.

Several useful methods for evaluating toughness thatdo not require determining It, e.g., ASTM C 1018 andJCI SF4,8 have been adopted. These methods are basedon the facts that: (a) it may not always be practical toobtain the complete P-d characteristics of FRC (timeconstraints in slow tests or rate-dependent behavior inrapid tests); (b) a stable fracture test of the unrein-forced beam requires a stiff testing machine, or closed-loop testing;9 (c) each toughness test using the It mea-sure would require both FRC and unreinforced beamsof identical matrix to be cast, cured, and tested; and (d)It does not reflect the relative toughness estimates atspecified levels of serviceability appropriate to specificapplications.

ASTM C 1018 provides a means for evaluating ser-viceability-based toughness indexes and the first-crackstrength of fiber reinforced concretes. The procedureinvolves determining the amount of energy required todeflect the FRC beam a selected multiple of the first-crack deflection based on serviceability considerations.This amount of energy is represented by the area underthe load-deflection curve up to the specified multiple ofthe first-crack deflection. The toughness index is cal-culated as the area under the P-d diagram up to theprescribed deflection, divided by the area under the P-ddiagram up to the first-crack deflection (first-cracktoughness).

Indexes Is, I10, and I30 at deflections of 3, 5.5, and15.5 times the first-crack deflection, respectively, areillustrated in Fig. 4. These indexes provide an indica-tion of (a) the relative toughness at these deflections,


Fig. 4-Toughness indexes from flexural load-deflection diagram

and (b) the approximate shape of the post-cracking P-dresponse. The indexes I5, I10, and I30 have a minimumvalue of 1 (elastic-brittle material behavior) and valuesof 5, 10, and 30, respectively, for perfectly elastic-plas-tic behavior (elastic up to first crack, perfectly plasticthereafter). The unreinforced matrix is assumed to beelastic-brittle. It is possible for the indexes thus definedto have values larger than their respective elastic-plasticvalues, depending on fiber type, volume fraction, andaspect ratio.

ASTM C 1018 requires that the first-crack strengthand the corresponding deflection and toughness be re-ported in addition to indexes I5, I10, and I30. In addi-tion, ASTM C 1018 allows extension of the toughnessindex rationale for calculation of greater indexes, suchas I 50 and I 100, to accomodate tougher fiber reinforcedcomposites such as slurry-infiltrated fiber reinforcedcomposites. However, as previously mentioned, It is ameasure of the improvement in toughness relative tothe unreinforced matrix, while I5, I10, and I30 providemeasures relative to a particular fiber mixture’s first-crack strength.

Some general observations listed in the followingparagraphs are pertinent to the recommendations justmentioned and may be found useful. Additional infor-mation is available in the references.5-7,9-11

a. ASTM C 1018 toughness indexes are intended forfiber reinforced concretes with substantial ductility.

b. Deflection measurements, especially of smallvalues such as the first-crack deflection, are subject tosignificant experimental error due to deflection of thebeam supports and specimen rocking (initially large).As a result, caution should be exercised when using andinterpreting these values to calculate toughness usingareas under the load-deflection curve.11

c. The energy absorption capacity recorded in thethird-point loading test (toughness, modulus of rupture

tests) will overestimate the true fracture energy of thecomposite, particularly if nonlinear deformations oc-cur at more than one cross section (occurrence of mul-tiple cracking in the middle third of the specimen).

FLEXURAL FATIGUE ENDURANCEThe endurance in dynamic cyclic flexural loading is

an important property of FRC, particularly in applica-tions involving repeated loadings, such as pavementsand industrial floor slabs. Although there is no currentstandard for flexural fatigue performance, testing sim-ilar to that employed for conventional concrete hasbeen conducted using reversing and nonreversing load-ing, with applied loads normally corresponding to 10 to90 percent of the static flexural strength.12 Short beamspecimens with small required deflection movementshave been successfully tested at 20 cycles per second(cps) when hydraulic testing machines with adequatepump capacity were available.12 However, verificationthat the full load and specimen response has beenachieved at these high frequencies is desirable. Speci-mens with large deflections may need to be tested at re-duced rates of 1 to 3 cps, to minimize inertia effects.Strain rates of 6000 to 10,000 microstrain per second(microstrain/sec) may result from testing at 20 cps ver-sus a strain rate of 600 to 1000 microstrain/sec at 2 cps.

Loadings are selected so that testing can continue toat least two million cycles, and applications to 10 mil-lion cycles are not uncommon. The user should beaware that 10 million cycles at 2 cps will require over 57days of continuous testing, and the influence ofstrength gain with time must be considered in additionto the influence of strain rates. Specimen testing at laterages may reduce the influence of aging when testing atthe lower strain rates.

Test results in the range of 60 to 90 percent of thestatic flexural strength for up to 10 million cycles have


been reported for nonreversed loading to steel fiberreinforced concrete with 0.5 to 1.0 volume percent fi-ber content.13 Data on reversed loading cyclic testingand the influence of strain rate and load versus timeparameters are not available.

SPLITTING TENSILE STRENGTHResults from the split cylinder tensile strength test

(ASTM C 496) for FRC specimens are difficult to in-terpret after the first matrix cracking and should not beused beyond first crack because of unknown stress dis-tributions after first crack.14 The precise identificationof the first crack in the split cylinder test can be diffi-cult without strain gages or other sophisticated meansof crack detection, such as accoustic emission or laserholography. 15,16 The relationship between splitting ten-sile strength and direct tensile strength or modulus ofrupture has not been determined.

The split cylinder tensile test has been used in pro-duction applications as a quality control test, after re-lationships have been developed with other propertieswhen using a constant mixture.

IMPACT RESISTANCEImproved impact resistance (dynamic energy absorp-

tion as well as strength) is one of the important attri-butes of FRC. Several types of tests have been used tomeasure the impact resistance of FRC. These can beclassified broadly, depending upon the impactingmechanism and parameters monitored during impact,into the following types of tests:17 (a) weighted pendu-lum Charpy-type impact test; (b) drop-weight test (sin-gle or repeated impact); (c) constant strain-rate test; (d)projectile impact test; (e) split-Hopkinson bar test; (f)explosive test; and (g) instrumented pendulum impacttest.

Conventionally, impact resistance has been charac-terized by a measure of (a) the energy consumed tofracture a notched beam specimen (computed from theresidual energy stored in the pendulum after impact);(b) the number of blows in a “repeated impact” test toachieve a prescribed level of distress; and (c) the size ofthe damage (crater/perforation/scab) or the size andvelocity of the spall after the specimen is struck with aprojectile or after the specimen is subjected to a sur-face blast loading.

Results from such tests are useful for ascertaining therelative merits of the different mixtures as well as forproviding answers to specific practical problems. How-ever, they depend on the specimen geometry, test sys-tem compliance, loading configuration, loading rate,and the prescribed failure criterion.17 The simplest ofthe conventional tests is the “repeated impact,” drop-weight test described in the next subsection.

More recently, instrumented impact tests have beendeveloped that provide reliable and continuous timehistories of the various parameters of interest duringthe impact-load, deflection, and strain.18 These pro-vide basic material properties at the various strain ratesfor the calculation of flexural/tensile strength, energy

Fig. 5-Plan view of test equipment for impactstrength. 13 Section A-A is shown in Fig. 6

absorption capacity, stiffness, and load-deformationcharacteristics. These types of tests are described in theinstrumented impact test subsection.

More information on the merits and drawbacks of allthe types of impact tests with particular emphasis ontheir usefulness for measuring the impact resistance ofFRC is also available.17,18

Drop-weight testThe simplest of the impact tests is the “repeated im-

pact,” drop-weight test. This test yields the number ofblows necessary to cause prescribed levels of distress inthe test specimen. This number serves as a qualitativeestimate of the energy absorbed by the specimen at thelevels of distress specified. The test can be used tocompare the relative merits of different fiber-concretemixtures and to demonstrate the improved perfor-mance of FRC compared to conventional concrete. Itcan also be adapted to show the relative impact resis-tance of different material thicknesses.19

Equipment - Referring to Fig. 5 and 6, the equipmentfor the drop-weight impact test consists of: (1) a stan-dard, manually operated 10 lb (4.54 kg) compactionhammer with an 18-in. (457-mm) drop (ASTM D 1557),(2) a 21/2 in. (63.5 mm) diameter hardened steel ball,and (3) a flat baseplate with positioning bracket similarto that shown in Fig. 5 and 6. In addition to this equip-ment, a mold to cast 6 in. (152 mm) diameter by 21/2 in.(63.5 mm) thick [±1/8 in., ± (3 mm)] concrete speci-mens is needed. This can be accomplished by usingstandard ASTM C 31 or C 470 molds.

Procedure - The 21/2 in. (63.5 mm) thick by 6 in. (152mm) diameter concrete samples are made in molds ac-cording to procedures recommended for compressivecylinders but using only one layer. The molds can befilled partially to the 21/2 in. (63.5 mm) depth and float-


Fig. 6-Section through test equipment for impact strength shown in Fig. 519

finished, or they can be sawn from full-size cylinders toyield a specimen size of the proper thickness. Speci-mens cut from full-size cylinders are preferred. If fi-bers longer than 0.80 in. (20 mm) are used, the testspecimen should be cut from a full-size cylinder tominimize preferential fiber alignment.

Specimens should be tested at 7, 28, and (if desired)90 days of age. Curing and handling of the specimensshould be similar to that used for compressive cylin-ders. Accelerated curing is not desirable. The thicknessof the specimens should be recorded to the nearest 1/16

in. (1.5 mm). The reported thickness should be deter-mined by averaging the measured thickness at the cen-ter and each edge of the specimen along any diameteracross the top surface. The samples are coated on thebottom with a thin layer of petroleum jelly or a heavygrease and placed on the baseplate within the position-ing lugs with the finished face up (if appropriate). Thepositioning bracket is then bolted in place, and thehardened steel ball is placed on top of the specimenwithin the bracket. Foamed elastomer pieces are placedbetween the specimen and positioning lugs to restrictmovement of the specimen during testing to the firstvisible crack.

The drop hammer is placed with its base upon thesteel ball and held there with just enough down pres-sure to keep it from bouncing off the ball during thetest. The baseplate should be bolted to a rigid base,such as a concrete floor or cast concrete block. An au-tomated system with a counter may also be used. Thehammer is dropped repeatedly, and the number ofblows required to cause the first visible crack on the topand to cause ultimate failure are both recorded. Thefoamed elastomer is removed after the first visiblecrack is observed. Ultimate failure is defined as theopening of cracks in the specimen sufficiently so that

the pieces of concrete are touching three of the fourpositioning lugs on the baseplate.

Results of these tests exhibit a high variability andmay vary considerably with the different types of mix-tures, fiber contents, etc.17

Instrumented impact testWhile retaining the conventional mechanisms to ap-

ply impact loads, instrumented impact tests permit themonitoring of load, deflection, strain, and energy his-tories during the impact event, manifested by a singleblow fracture. This allows the computation of basicmaterial properties such as fracture toughness, energydissipation, ultimate strength, and corresponding strainor deformation at different strain rates of loading.

Instrumented impact testing has been applied suc-cessfully to fiber reinforced concrete. Two types of sys-tems are commonly used: a drop-weight-type systemand a pendulum-type system (Charpy impact system).Instrumentation of these systems is quite complex andimplies instrumentation of the striker as well as the an-vil supports that act as load cells.20-22

In the instrumented drop weight system [Fig. 7(a)], aweight equipped with a striker is dropped by gravity onthe specimen while guided by two columns. The Charpysystem [Fig. 7(b)] uses a free-falling pendulum weightequipped with a striker as the impacting mechanism.The weight of the impacter and the drop height in bothsystems provide a range of impact velocities and energycapacities for the impact test. In comparing Fig. 7(a)and 7(b), it can be observed that the electronic instru-mentation is the same for both systems even though themechanical configurations of the drop weight and theCharpy systems are different.

Instrumentation for instrumented impact testing in-cludes dynamic load cells, foil-type resistance gages for


Fig. 7(a)-Block diagram of the general layout of the instrumented drop weightsystem22

Fig. 7(b)-Block diagram of the general layout of the modified instrumentedCharpy system20

strain measurements, and associated signal condition-ing amplifiers and storage oscilloscope (preferably dig-ital). All electronic equipment must have adequatehigh-frequency response to monitor and record alltransducer outputs without distortions during the shortimpact event ( < 1 millisecond).

Simultaneous electronic recording of the anvil andstriker loads is essential for the proper interpretation ofinertial loads and to assess the influence on the resultsof parameters such as test system compliance, speci-men size, and impact velocity. The anvils and thestriker should be designed to serve as dynamic load cellsand to insure elastic behavior even under high loads.They should be sufficiently rounded at the specimencontact points to avoid local compression damage tothe specimen on impact and to facilitate specimen ro-

tation during bending. The load cells are instrumentedusing semiconductor strain gages mounted in full bridgeconfiguration within protective recesses provided oneither side of each cell (anvil and striker). The fullbridge configuration is recommended for high signal-to-noise ratio and to allow for temperature compen-sation. Output signals from the two anvils should beconnected in series to monitor the total load at thesupports.

Problems of parasitic inertial loads in the responsesrecorded from instrumented impact tests and recom-mendations to overcome them are detailed in Reference22. As a general guideline, test parameters should beselected so that the difference between the striker andanvil loads recorded during the test does not exceed 5percent.


FREEZE-THAW RESISTANCEASTM C 666 is applicable to FRC. Weight loss is not

a recommended method for determining the freeze-thaw resistance of FRC because material that becomesdislodged from the specimen mass remains looselybonded by the fibers. The relative dynamic modulus ofelasticity method is appropriate for FRC.

Inclusion of fibers should not be considered as asubstitute for proper air entrainment to obtain freeze-thaw resistance.

LENGTH CHANGE (SHRINKAGE)Unrestrained shrinkage

For length change of concrete, ASTM C 157 andC 341 are applicable to FRC. ASTM C 341 is the pre-ferred test method since the test specimens are cut fromlarger cast concrete samples; thus, the influence on fi-ber orientation from casting specimens in smaller moldsis minimized. However, these tests do not reflect theperformance of FRC in early age shrinkage and crackcontrol.

Restrained shrinkageASTM C 827 for early volume change of cementi-

tious mixtures is also applicable to FRC. The degree ofrestraint to which the specimen is subjected varies withthe viscosity and degree of hardening of the mixture sothat measurements are useful primarily for compara-tive purposes rather than as absolute values.

RESISTANCE TO PLASTIC SHRINKAGECRACKING

The lack of a standard test for plastic shrinkagecracking resistance of concrete at an early age hasprompted the proposal of several methods. These in-volve measurement of the length and width of concretecracks. Ring, rectangular, square, and combinations ofthese shapes (shown in Fig. 8) have been used to char-acterize the crack resistance characteristics of FRCcompared to nonfiber reinforced concrete.23-25 Thethickness of the specimens varies from 1/4 to 6 in. (6 to152 mm), depending on the maximum size aggregate,fiber length, and application.

The specimens form cracks at the top surface and re-straint is necessary for the cracks to occur. Bondbreakers are employed on the horizontal surfaces of thespecimen form to minimize surface restraint at thebase. External restraint may be provided by casting inwelded wire fabric attached to the form or an internalrestraining ring, as shown by dashed lines in Fig. 8.

Measurements of cracking resistance are quantifiedby summing the product of the length and width of thecracks and expressing the results as a percentage incomparison to nonfibrous concrete at a 24-hr age. Mostmicrocracks occur in the mortar fraction of the con-crete within the first few hours when subjected to evap-oration rates in excess of 0.15 lb of moisture loss per ft2

per hr (0.732 kg/m2/hr). A wind tunnel has been usedto control the evaporation rate of the test specimens.More details regarding these proposed test methods can

Note: Dashed Lines Indicate Restraint

Fig. 8-Comparison of crack resistance characteristicsof FRC to nonfiber reinforced concrete

be found in References 23 through 25. The relationshipbetween these test results and field applications has notbeen determined.

CREEPASTM C 512 test for creep in concrete is applicable

to FRC.

MODULUS OF ELASTICITY AND POISSON’SRATIO

ASTM C 469 test for modulus of elasticity and Pois-son’s ratio is applicable to FRC.

CAVITATION, EROSION, AND ABRASIONRESISTANCE

As with conventional concrete, testing FRC for cavi-tation, erosion, and/or abrasion resistance according toASTM C 418 and C 779 is extremely difficult if realis-tic and practical results are to be obtained. Any of thesespecial tests should be evaluated carefully, and theirspecific applicability to a job should be considered.Whenever possible, large-size specimens should be castand tested for these types of evaluations. Every effortshould be made to include tests under conditions ex-pected to be experienced in service.

An example of full-scale testing is the U.S. ArmyCorps of Engineers’ hydraulic test flume for cavita-tion/erosion at Detroit Dam.26 Erosion with small de-bris and low fluid velocity can be investigated by theCorps of Engineers’ method CRD-C 63.

REFERENCESRecommended references

The documents of the various standards-producingorganizations referred to in this report follow with their


serial designation, including year of adoption or revi-sion. The documents listed were the latest revision atthe time this report was published. Since some of thesedocuments are revised frequently, generally in minordetail only, the user of this report should check directlywith the sponsoring group if it is desired to refer to thelatest revision.

American Concrete Institute506.1R-84

506.2-77(Revised 1983)

544.1R-82(Reapproved 1986)544.3R-84

SP-44SP-81

SP-109

ASTMA 820-85

C 31-87a

C 39-86

C 42-85

C 78-84

C 138-81

C 157-86

C 173-78

C 192-81

C 231-82

C 293-79

State-of-the-Art Report on FiberReinforced ShotcreteSpecification for Materials, Pro-portioning, and Application ofShotcreteState-of-the-Art Report on FiberReinforced ConcreteGuide for Specifying, Mixing,Placing, and Finishing Steel Fi-ber Reinforced ConcreteFiber Reinforced ConcreteFiber Reinforced Concrete-In-ternational SymposiumFiber Reinforced Concrete Prop-erties and Applications

Standard Specification for SteelFibers for Fiber Reinforced Con-creteStandard Practice for Makingand Curing Concrete Test Speci-mens in the FieldStandard Test Method for Com-pressive Strength of CylindricalConcrete SpecimensStandard Method of Obtainingand Testing Drilled Cores andSawed Beams of ConcreteStandard Test Method for Flex-ural Strength of Concrete (UsingSimple Beam with Third-PointLoading)Standard Test Method for UnitWeight, Yield, and Air Content(Gravimetric) of ConcreteStandard Test Method for LengthChange of Hardened Hydraulic-Cement Mortar and ConcreteStandard Test Method for AirContent of Freshly Mixed Con-crete by the Volumetric MethodStandard Method of Making andCuring Concrete Test Specimensin the LaboratoryStandard Test Method for AirContent of Freshly Mixed Con-crete by the Pressure MethodStandard Test Method for Flex-ural Strength of Concrete (UsingSimple Beam with Center-PointLoading)

C 341-84

C 418-81

C 469-87

C 470-87

C 496-86

C 512-87

C 666-84

C 779-82

C 827-87

C 995-86

C 1018-85

D 1557-78

Standard Test Method for LengthChange of Drilled or SawedSpecimens of Cement Mortar andConcreteStandard Test Method of Abra-sion Resistance of Concrete bySandblastingStandard Test Method for StaticModulus of Elasticity and Pois-son’s Ratio of Concrete in Com-pressionStandard Specification for Moldsfor Forming Concrete Test Cyl-inders VerticallyStandard Test Method for Split-ting Tensile Strength of Cylindri-cal Concrete SpecimensStandard Test Method for Creepof Concrete in CompressionStandard Test Method for Resis-tance of Concrete to RapidFreezing and ThawingStandard Test Method for Abra-sion Resistance of HorizontalConcrete SurfacesStandard Tes t Method forChange in Height at Early Agesof Cylindrical Specimens fromCementitious MixturesStandard Test Method for Timeof Flow of Fiber-ReinforcedConcrete Through InvertedSlump ConeStandard Test Method for Flex-ural Toughness and First-CrackStrength of Fiber-ReinforcedConcrete (Using Beam withThird-Point Loading)Standard Test Methods for Mois-ture-Density Relations of Soilsand Soil-Aggregate Mixtures Us-ing 10-lb (4.54-kg) Rammer and18-in. (475-mm) Drop

British Standards InstitutionBS 1881:Part 2 Methods of Testing Concrete

U.S. Army Corps of EngineersCRD-C 63-80 Test Method for Abrasion-Erosion

Resistance of Concrete (UnderwaterMethod)

These publications may be obtained from the follow-ing organizations:

American Concrete InstituteP.O. Box 19150Detroit, MI 48219-0150


ASTM1916 Race StreetPhiladelphia, PA 19103

British Standards InstitutionLinford WoodMilton Keynes MK14 6LEEngland

U.S. Army Corps of EngineersWaterways Experiment StationP.O. Box 631Vicksburg, MS 39180

Cited references1. “Recommended Practice for Glass Fiber Reinforced Concrete

Panels,” Journal, Prestressed Concrete Institute, V. 26, No. 1, Jan.-Feb. 1981, pp. 25-93.

2. “GRCA Methods of Testing Glassfibre Reinforced Cement(CRC) Material,” (GRCA S0103/0481), Glassfibre Reinforced Ce-ment Association, Gerrands Cross, Bucks, 1981, 32 pp.

3. Johnston, Colin D., “Measures of the Workability of Steel Fi-ber Reinforced Concrete and Their Precision,” Cement, Concrete,and Aggregates, V. 6, No. 2, Winter 1984, pp. 74-83.

4. Johnston, C. D., “Precision of Flexural Strength and Tough-ness Parameters for Fiber Reinforced Concrete,” Cement, Concrete,and Aggregates, V. 4, No. 2, Winter 1982, pp. 61-67.

5. Johnston, C. D., “Definition and Measurement of FlexuralToughness Parameters for Fiber Reinforced Concrete,” Cement,Concrete, and Aggregates, V. 4, No. 2, Winter 1982, pp. 53-60.

6. Johnston, Colin D., “Toughness of Steel Fiber ReinforcedConcrete,” Steel Fiber Concrete, Swedish Cement and Concrete Re-search Institute, Stockholm, 1985, pp. 333-360.

7. Shah, Surendra P.; Ludirja, Darmawan; and Daniel, James I.,“Toughness of Glass Fiber Reinforced Concrete Panels Subjected toAccelerated Aging,” Journal, Prestressed Concrete Institute, V. 32,No. 5, Sept.-Oct. 1987, pp. 82-99.

8. “Method of Test for Flexural Toughness Parameters for FiberReinforced Concrete,” Standard SF4, JCI Standards for Test Meth-ods of Fiber Reinforced Concrete, Japan Concrete Institute, Tokyo,1983, pp. 45-51.

9. Jenq, Y. S., and Shah, S. P., “Crack Propagation Resistance ofFiber-Reinforced Concrete,” Journal of Structural Engineering,ASCE, V. 112, No. 1, Jan. 1986, pp. 19-34.

10. Shah, Surendra P., and Skarnedahl, Åke, Editors, Steel FiberConcrete, Elsevier Applied Science Publishers, 1985, 520 pp.

11. Kobayashi, K., and Umeyama, K., “Methods of Testing Flex-ural Toughness of Steel Fiber Reinforced Concrete,” Report, De-partment of Building and Civil Engineering, Institute of IndustrialScience, University of Tokyo, 1980.

12. Ramakrishnan, V.; Brandshaug, Terje; Coyle, W. V.; andSchrader, Ernest K., “A Comparative Evaluation of Concrete Rein-

forced with Straight Steel Fibers and Fibers with Deformed EndsGlued Together into Bundles,” ACI JOURNAL, Proceedings V. 77,No. 3, May-June 1980, pp. 135-143.

13. Ramakrishnan, V.; Oberling, G.; and Tatnall, P., “FlexuralFatigue Strength of Steel Fiber Reinforced Concrete,” Fiber Rein-forced Concrete-Properties and Applications, SP-105, AmericanConcrete Institute, Detroit, 1987, pp. 225-245.

14. Schrader, Ernest K., “Formulating Guidance for Testing ofFibre Concrete in ACI Committee 544,” Proceedings, RILEM Sym-posium on Testing and Test Methods of Fibre Cement Composites,Construction Press Ltd., Lancaster, 1978, pp. 9-21.

15. Maji, A. K., and Shah, S. P., “Process Zone and AcousticEmission Measurements in Concrete,” Experimental Mechanics, V.28, No. 1, Mar. 1988, pp. 27-33.

16. Miller, R. A.; Shah, S. P.; and Bjelkhagen, H. I., “CrackProfiles in Mortar Measured by Hollographic Interferrometry,” Ex-perimental Mechanics, in press.

17. Gopalaratnam, V. S., and Shah, S. P., “Properties of FiberReinforced Concrete Subjected to Impact Loading,” ACI JOURNAL,Proceedings V. 83, No. 1, Jan.-Feb. 1986, pp. 117-126.

18. Suaris, Wimal, and Shah, Surendra P., “Properties of Con-crete Subjected to Impact,” Journal of Structural Engineering,ASCE, V. 109, No. 7, July 1983, pp. 1727-1741.

19. Schrader, Ernest K., “Impact Resistance and Test Procedurefor Concrete,” ACI JOURNAL, Proceedings V. 78, No. 2, Mar.-Apr.1981, pp. 141-146.

20. Gopalaratnam, V. S.; Shah, S. P.; and John, R., “A ModifiedInstrumented Charpy Test for Cement-Based Composites,” Experi-mental Mechanics, V. 24, No. 2, June 1984, pp. 102-111.

21. Naaman, A. E., and Gopalaratnam, V. S., “Impact Propertiesof Steel Fibre Reinforced Concrete in Bending,” International Jour-nal of Cement Composites and Lightweight Concrete (Harlow), V. 5,No. 4, Nov. 1983, pp. 225-233.

22. Suaris, W., and Shah, S. P., “Inertial Effects in the Instru-mented Impact Testing of Cementitious Composites,” Cement, Con-crete, and Aggregates, V. 3, No. 2, Winter 1981, pp. 77-83.

23. Swamy, R. N., and Stavrides, H., “Influence of Fiber Rein-forcement on Restrained Shrinkage and Cracking,” ACI JOURNAL ,Proceedings V. 76, No. 3, Mar. 1979, pp. 443-460.

24. Dahl, Per Arne, “Plastic Shrinkage and Cracking Tendency ofMortar and Concrete Containing Fibermesh,” Report, ISBN No. 82-4060-6, FCB Cement and Concrete Institute, Trondheim, Nov. 9,1985, pp. l-23.

25. Kraai, P. P., “A Proposed Test to Determine the CrackingPotential Due to Drying Shrinkage of Concrete,” Concrete Con-struction Publications, Addison, Sept. 1986, 77 pp.

26. Houghton, D. L.; Borge, O. E.; and Paxton, J. A., “Cavita-tion Resistance of Some Special Concretes,” ACI JOURNAL, Pro-ceedings V. 75, No. 12, Dec. 1978, pp. 664-667.

This report was submitted to letter ballot of the committee and was ap-proved in accordance with ACI balloting procedures.

THE FOLLOWING DISCUSSIONS, WHICH WERE PUBLISHED IN THE JULY-AUGUST 1989 ACI StructuralJournal (PP. 425-426), ARE NOT PART OF THE REPORT ACI 544.2R-89, BUT ARE PROVIDED ASADDITIONAL INFORMATION TO THE READER.

Measurement of Properties of Fiber Reinforced Concrete. Report by ACI Committee 544

Discussion by Nemkumar Banthia and Committee

By NEMKUMAR BANTHIAMember American Concrete Institute, Assistant Research Professor,Department of Civil Engineering, Laval University, Quebec

The committee is to be congratulated for developinga comprehensive report on testing fiber reinforced con-crete that is timely, informative, and useful. However,I would like to raise a few points concerning the impacttesting of concrete.

1. In any dynamic testing, a sudden change in themomentum of the system is bound to produce d’Alam-bert’s forces or the inertial forces due to specimen ac-celerations. One way of dealing with the specimen in-ertia, as suggested in the report, is to vary the stiffnessof the contact zone (by introducing a soft rubber pad)and/or by choosing the test parameters, such as thespecimen dimensions, hammer/specimen mass ratio,etc., such that the peak load occurs only after the spec-imen has gained enough momentum and is no longeraccelerating. This is indeed an ingenious method ofdealing with the inertial forces; however, the introduc-tion of the rubber pad leads to a considerable reduc-tion in the applied stress-rate on the specimen,27 and therestricted test parameters lead to a limited scope intesting. In my opinion, for dynamic testing, a properdynamic analysis of the system is necessary. One way todo so is by actually measuring the specimen accelera-tions by piezo-electric accelerometers.28,*,† Once the ac-celerations are known, a proper dynamic analysis of thesystem is possible, and the load-versus-load point dis-placement plots may be obtained. Moreover, there areno restrictions in the choice of the test parameters andvery high stress rates may be generated.

All the dynamic data-acquisition systems have a lim-ited number of input channels. It may appear that toknow the accelerations at every point, a large numberof accelerometers are required with an equal number ofinput data channels. Fortunately, the specimen accel-erations are often simple mathematical functions of thespatial coordinates,27 and the experimental measure-ment of accelerations is necessary only at one or twoselected points on the specimen.

2. In the case of the longer flexural specimens, a cer-tain time-lag between the striker and the anvil load ispossible with the anvil load peak lagging behind thestriker load peak.† A comparison between the two,therefore, warrants caution. Furthermore, the total

*Banthia, N.; Mindess, S.; Bentur, A.; and Pigeon, M., “Impact Testing ofConcrete Using a Drop Weight Impact Machine,” Experimental Mechanics, inpress.

†Banthia, N., and Lhama, Y., “Dynamic Tensile Fracture of Carbon FibreCements,” International Conference on Recent Developments in Fibre Rein-forced Cements and Concretes, Cardiff, Sept. 1989, in press.

support load plotted against the measured load-pointdisplacement, in a three-point bend test using time-based data, may yield an improper load-versus-dis-placement plot.

REFERENCES27. Banthia, N., “Impact Resistance of Concrete,” PhD thesis,

University of British Columbia, Vancouver, 1987.28. Banthia, N. P.; Mindess, Sidney; and Bentur, Arnon, “Impact

Behaviour of Concrete Beams,” Materials and Structures, Researchand Testing (RILEM, Paris), V. 20, NO. 118, July 1987, pp. 293-302.

COMMITTEE CLOSUREThe committee appreciates the discussion by Dr.

Banthia. He suggests an alternate method of analyzingthe results from the instrumented impact tests. It is cer-tainly possible to measure the inertial forces that aspecimen is subjected to during an impact event. Theseforces can then be subtracted from the measured tupload to evaluate the bending stresses experienced by thebeam. This method can extend the range of the loadingrate, which is possible with an instrumented testing sys-tem described in the committee report. Unfortunatelythere can be other problems with the method suggestedby Dr. Banthia: 1) Flexural load experienced by thebeam is the difference between two large numbers(measured tup load and calculated inertial forces). Thisreduces the accuracy of the result; 2) unless a largenumber of accelerometers are used, assumptions re-garding the deflected shape of the beam have to bemade; and 3) unless dynamic finite element analysiswith singular elements is used, it is difficult to calculatefracture toughness for notched beams.

If the beam is unusually long and the rate of loadingis unusually high, there may be a time lag between thetup load and the anvil load. Usually this is not a prob-lem for fiber reinforced concrete beams.

In summary, the instrumented test method recom-mended by the committee is an accurate method to de-termine the rate effects on modulus of rupture values aswell as fracture toughness values for concrete and fiberreinforced concrete.

For very high rates of loading, alternate methods ofinstrumentation and analysis are needed. A detaileddiscussion of different test methods for high-velocityimpact loading can be found in Reference 29.

REFERENCE29. John, R., and Shah, S. P., “Constitutive Modeling of Con-

crete under Impact Loading,” Proceedings, 1st International Con-ference on Effects of Fast Transient Loadings, Balkema Publishers,1988.

544.2R-D1