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Committee Repo rt on Fiber Rein forced Shotcrete

ACI 506.1R-98

Reported by ACI Committee 506

————

*Subcommittee members who prepared this report.**Subcommittee chairman who prepared this report.

Steven H. GeblerChairman

Lars F. Balck, Jr.Secretary

Jon B. Ardahl*Denis Beaupre*Ric W. Berndt*

Seymour A. BortzPaul D. Carter*

Gary L. ChynowethJames L. Cope*John R. Fichter

I. Leon GlassgoldJill E. Glassgold

Warren L. HarrisonMerlyn Isaak

Richard A. KadenBruce K. Langson*

Albert LitvinKristian Loevlie

Dudley R. MorganDirk E. Nemegeer*Joseph Ostrowski*

H. Celik OzyildirimHarvey W. ParkerDale A. PearceyJohn E. Perry, Jr.

John Pye*Venkataswamy Ramakrishnan*

Thomas J. ReadingPaul E. Reinhart

Ernest K. Schrader*Vern Schultheis

Raymond J. SchutzPhilip T. Seabrook**

W. L. Snow, Sr.Curt E. Straub

Lawrence J. Totten*Gary L. Vondran*R. Curtis White, Jr.

George Yoggy*John W. Zimmerman

ACI Committee Reports, Guides, Standard Practices, aCommentaries are intended for guidance in planning, dsigning, executing, and inspecting construction. This doc-ument is intended for the use of individuals who arcompetent to evaluate the significance and limitationof its content and recommendations and who wil l acceptresponsibility for the application of the material it contains. The American Concrete Institute disclaims any anall responsibility for the stated principles. The Institute shanot be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contradocuments. If items found in this document are desireby the Architect/Engineer to be a part of the contract douments, they shall be restated in mandatory language incorporation by the Architect/Engineer.

506.1

ACI 506.1R-98 became effective April 8, 1998. This report supercedes ACI 506.1R-84. Copyright 1998, American Concrete Institute.

All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, or recording for sound or visual reprodution or for use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors.

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This report describes the technology and uses of fiber reinforced shotcretesusing steel and polypropylene fibers. Mechanical properties, particularly duc-tilit y, toughness, impact strength, and flexural strength are improved by thefiber addition, and these improvements are described along with other typicaproperties and proportions of typical mixes. Batching, mixing, and applicationprocedures are described, including methods of reducing rebound and equip-ment used to apply fiber reinforced shotcrete. Applications of fiber reinforcedshotcrete in North America, Europe, and Scandinavian countries are

described. These include rock slope stabilization work, construction andrepair of mine and tunnel linings, bridge arch strengthening, anddome-shaped structures. Available design information is briefly discussed anddesign references are listed.

Keywords: fiber reinforced concretes; fibers; linings; metal fibers; mines;mixture proportioning; placing; polypropylene fibers; shotcrete; slope pro-tection; stabilization; steel strength; toughness; tunnel linings.

CONTENTS

Chapter 1—Int roduction, p. 506.1R-21.1—Definition of fiber reinforced shotcrete

1.2—Fiber types

1.3—General

1.4—Historical background

1.5—Tests for fiber reinforced concrete and shotcrete

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506.1R-2 ACI COMMITTEE REPORT

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Chapter 2—Steel fiber rein forced shotcret e,p. 506.1R-3

2.1—General 2.2—Fiber types 2.3—Typical material properties 2.4—Mix compositions 2.5—Batching and mixing 2.6—Installation 2.7—Applications 2.8—Available design information

Chapter 3—Synthetic fiber rein forced shotcret e,p. 506.1R-10

3.1—Polypropylene fiber reinforced shotcrete 3.2—Shotcrete using other synthetic fibers

Chapter 4—References, p. 506.1R-104.1—Specified and/or recommended references 4.2—Cited references4.3—General references

CHAPTER 1—INTRODUCTION 1.1—Definition of fiber rein forced shotcrete

Fiber reinforced shotcrete is mortar or concrete containdiscontinuous discrete fibers that is pneumatically projecat high velocity onto a surface. Continuous meshes, wofabrics, and long rods are not considered to be discretber-type reinforcing elements in this report.

1.2—Fiber types Fibers for shotcrete can be made of steel, glass, synth

and natural materials. For purposes here, only steel polypropylene will be considered since they represent bythe most commonly used types.

One parameter used to characterize a fiber is its aspectio, defined as the fiber length divided by its diameter orequivalent fiber diameter.*

Typical aspect ratios range from about 30 to 150 for lendimensions of 0.25 to 3 in. (6 to 75 mm). For shotcrete, comon lengths are 0.75 to 1.5 in. (20 to 40 mm).

Typical fiber diameters are: Steel—0.010 to 0.030 in. (0.25 to 0.76 mm) Synthetic—0.0008 to 0.02 in. (0.02 to 0.5 mm)

Additional information on fibers may be found in AC544.1R.

ASTM A 820 is a specification defining the required proerties of steel fibers.

1.3—General The inclusion of fibers in concrete and shotcrete gener

improves material properties including ductility, toughneflexural strength, impact resistance, fatigue resistance, to a small degree, compressive strength. The type amount of improvement is dependent upon the fiber ty

* The equivalent diameter is the diameter of a circle having an area equal to the cross-sectional area of a fiber.

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size, strength and configuration, and the amount of fiber. Othe two types, steel fiber reinforced shotcrete accounts fothe largest usage, having applications in mine and tunnelinings, rock slope stabilization, thin shell dome construc-tion, refractory linings, dam construction, repair of surfaces,and fire protection coatings.1,2

Polypropylene fiber shotcrete has also been used.3 Its usehas been reported in thin shell domes, repair of surfaces, anas a component in stucco-type overlayment systemsPolypropylene fiber shotcrete’s use has grown significantlyover the last decade.

A report by the U.S. Bureau of Mines4 presents a compre-hensive comparison of glass, steel, and fibrillated polypro-pylene fiber reinforced shotcrete properties used in underground applications. It states:

“Results indicate that all of the commercially available fiber gunitematerials tested can provide a beneficial sealant, spall prevention, orroof stability control attributes for underground mining environmentswhen applied by an experienced crew using a well-maintained gun, inaccordance with product manufacturers’ recommendations and whenused for the designated purpose.”

A compilation of international experience on shotcrete,particularly for rock support, was prepared by the Internation-al Tunnelling Association.5 It compares fiber reinforced andplain shotcrete; the report dwells primarily on steel fiber buthas some data on synthetic fibers.

1.4—Historical ba ckground Fiber reinforced shotcrete using steel fibers was first placed

in North America early in 1971 in experimental work underthe direction of D. R. Lankard of Battelle Memorial Institute’sColumbus Laboratories.6 Steel fiber reinforced shotcrete wasproposed for underground support under the direction of HW. Parker at the University of Illinois in 1971.7 Additional tri-als were made under the direction of M. E. Poad for the U.SBureau of Mines in an investigation of new and improvedmethods of using shotcrete for underground support.8 Subse-quently, R. A. Kaden of the U.S. Corps of Engineers supervised the first practical application of steel fiber reinforcedshotcrete in a tunnel adit at Ririe Dam, Idaho, in 1973.9 Sincethat time, steel fiber reinforced shotcrete has been placed iGermany (Stahlfaserspritzbeton), Sweden (StalfiberarmeraSprubeton), England, Norway, Finland, Switzerland, PolandSouth Africa, Australia, Canada, and Japan.

Shotcrete using polypropylene fibers was first placed inEurope in 1968.10

1.5—Tests for fiber rein forced concrete and shotcrete

Properties of fiber reinforced concrete are generally measured by tests advocated in ACI 544.2R; these are equallapplicable to shotcrete. ASTM tests directly applicable to fi-ber reinforced concrete and shotcrete are mentioned in AC544.2R. One of these, ASTM C 1018, is the most importanbecause it evaluates the post-cracking performance of fibereinforced concrete and shotcrete.

506.1R-3ER REINFORCED SHOTCRETE

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COMMITTEE REPORT ON FIB

CHAPTER 2—STEEL FIBER REINFORCED SHOTCRETE

2.1—General Steel fiber reinforced shotcrete is essentially a conventi

al shotcrete to which steel fibers have been added. Iplaced using the same mixing and placing equipment ufor conventional shotcrete. Some specialized equipment nozzles have been developed to aid in metering and adindividual fibers and for shooting, but special equipmentgenerally not required for mixing and placing. It can bplaced by either the wet-mix or dry-mix process.

Steel fiber reinforced shotcrete incorporates steel fibersto 2 percent by volume of the total mix. Improvements flexural strength, ductility, and toughness are sufficient enable it to be used as a replacement for steel mesh forced shotcrete in certain instances, such as rock slopebilization, mine and tunnel linings, and thin shell structureThe improvements in toughness and flexural strength evaluated by ASTM C 1018 and are evident in the modefailure; large deformations are required to cause compseparation of steel fiber reinforced shotcrete, and it continto carry a significant load after cracking. This post-crack sistance has been cited as providing ductility to tshotcrete11,12 and works to an advantage in applicationwhere there may be relatively large deformations such amine linings and tunnel linings.

2.2—Fiber types Steel fibers are manufactured by at least three proces

1) cutting cold drawn wire, 2) slitting steel sheet, and extracting them from a pool of molten steel (melt-extration). Wire fibers with bent or deformed ends have a higer pullout resistance than straight fibers and may be uin smaller quantities to achieve similar properties. The timate tensile strength of fibers varies from 50,000 to ov300,000 psi (345 to 2070 MPa). Fiber sizes range from1/2x 0.010 in. to 21/2 x 0.030 in. (13 x 0.25 mm to 64 x 0.76mm). A popular fiber size range for shotcrete is 3/4 to 11/4in. length x about 0.016 in. diameter (19 to 32 x 0.40 mmThis size range is easily handled and is normally shthrough a 2-in.-(50-mm)-diameter hose.

Steel fibers are used in applications at ambient tempetures and in some high temperature applications, up to 15(815 C) for elements heated from one side only. Stainless steelfibers are used in refractory concrete, both cast and shotcrefor high temperature applications up to 3000 F (1650 C) forements heated from one side only.13 See ACI 547R and Refer-ence 14 for additional data on refractory shotcrete with fibe

Corrosion of steel fibers has been found to be minimwith no adverse effect on flexural strength after 7 yearsexposure of steel fiber concrete to deicing salts. Tests oneffects of outdoor weathering in an industrial atmosphere10 years and in a marine exposure for 12 years have shno adverse effects on strength properties of steel fiber rforced mortar. Fiber corrosion was confined to fibers actuaexposed on a surface. Internal fibers showed no corrosFor references and additional data, see ACI 544.1R.

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2.3—Typical material p ropertiesUnless otherwise indicated herein, data is for steel fiber r

inforced shotcrete.2.3.1 Flexural and compressive strengths—Typical

28-day flexural strengths as determined from beam spemens vary from about 600 to about 1500 psi (4.1 to 10MPa) with typical values of 800 to 1100 psi (5.5 to 7.6MPa).15 These flexural strengths were determined using 4 x4 x 14-in. (100 x 100 x 350-mm) beams sawed from testpanels and tested on a 12-in. (305-mm) span in accordanwith ASTM C 78. In one investigation, the U.S. Bureau oMines reported flexural strengths of 4617 psi (31.9 MPa) fofibrous shotcrete and 2244 psi (15.5 MPa) for the plain, cotrol shotcrete using regulated-set cement and 2 percent volume of fibers.16 These were 360-day strengths determined by ASTM C 78 as described above. BESAB, a shocrete equipment manufacturer and applicator in Swedereported flexural strengths of about 2900 psi (20 MPa) omaterial placed with a special wet process nozzle using bers with an aspect ratio of 100 at 1 to 2 percent by volum

Placement of the shotcrete tends to orient the fibers inplane parallel to the surface being shot.12 This orientation isof benefit to the flexural properties of the shotcrete layer.

Compressive strengths at 28 days from mixes such asTable 2.3.1 have varied from about 4200 to 7500 psi (29 t52 MPa).15

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Table 2.3.1—Typical steel fiber rein forced shotcrete mixes (Reference 15, p. 52)

MaterialFine aggregate mix,

lb/yd3 (kg/m3)

3/8 in. (9 mm) aggregate mix, lb/yd3 (kg/m3)

Cement 753 to 940 (446 to 558) 750 (445)

Blended sand—1/4 in. (6 mm) maximum

2830 to 2500(1679 to 1483)

1485 to 1175(880 to 697)

3/8 in. (9 mm)aggregate

— 1180 to 1475(700 to 875)

Steel fiber 66 to 265 (39 to 157) 66 to 250 (39 to 150)

Accelerator Varies Varies

Water-cement, by weight 0.40 to 0.45 0.40 to 0.45

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In some instances, the compressive strength of the fibrousshotcrete has been lower (10 to 20 percent) than the contromix. This is believed due to less compaction in the shotcretecaused by the presence of the fibers. However, in some in-stances, the compressive strength of the fibrous shotcrete habeen up to 50 percent stronger than the plain control mix.15

2.3.2 Impact resistance—Impact resistance of steel fiberreinforced shotcrete is measured by a test that uses a 10 l(4.5 kg) hammer falling onto a steel ball centered on a 11/2to 21/2-in.-thick x 6-in.-diameter disc specimen (38 to 63mm thick x 150 mm diameter) as described in ACI 544.2R.The number of blows required to crack and separate fiber re-inforced specimens at 28 days ranges from about 100 to 500depending on the fiber amount, length, and configuration.Plain shotcrete specimens normally fail at 10 to 40blows.17,18

506.1R-4 ACI COMMITTEE REPORT

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2.3.3 Toughness—The amount of energy required tcause failure of fiber reinforced concrete by complete seration varies with the type and amount of fiber. Typical vaues of flexural toughness for small beams 4 x 4 x 14 in. (100x 100 x 350 mm) are in the range of 10 to 20 times that otained for plain concrete. This is reported as toughness oa toughness index.

The test procedure for flexural toughness is ASTM1018. There is currently considerable discussion on methods of interpreting results from ASTM C 1018 for fibreinforced shotcrete. The discussion in the Appendix ASTM C 1018 assists. However, there is agreement thataddition of steel fibers, and to a lesser degree polypropylegreatly increases toughness values.19

2.3.4 Pullout strength—Tests have been made using puout anchors that are embedded in the shotcrete as gunned. The pullout anchors, similar to those describedASTM C 900, were discs about 1 in. (25 mm) in diametembedded about 11/4 in. (30 mm) deep. In plain shotcretepullout test results show a linear relationship to compressstrength. For steel fiber reinforced shotcrete, a similaritythe magnitude and shape of strength-time curves for puland flexural strength (ASTM C 78) has been reported12

Tests on fibrous concrete placed on an open pit mine slopCanada gave results shown in Table 2.3.4.

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Table 2.3.4—Fou rteen d ay pullout strengths 15

MixPullout strength,

psi (MPa)

Plain shotcrete* 1000 (6.9)

Fibrous shotcrete† 1800 (12.4)

*750 lb (341 kg) cement, 1825 lb (830 kg) 3/8-in. (9.5-mm) stone, 1175 lb (534 kg)sand, 5 lb (2.3 kg) Barra Gunit 2 accelerator.

†750 lb (341 kg) cement, 1475 lb (670 kg) 3/8-in. (9.5-mm) stone, 1300 lb (591 kg)

sand, 250 lb (114 kg) fibers 0.010 × 1/2 in. (0.25 × 13 mm), 5 lb (2.3 kg) Barra Gunit2 accelerator.

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2.3.5 Tensile strain at 90 percent ultimate load(strain-to-failure) —Kaden9 made rapid load flexural tesof shotcrete specimens (4 x 4 x 12 in.; 100 x 100 x 305 mm)and found significantly increased strain-to-failure in the sfibrous material. Tensile strain in the outer beam fibers apercent of ultimate load ranged from 320 to 440 microstfor steel fibrous shotcrete at 28 days versus 192 microsfor plain shotcrete.

2.3.6 Bond strength—BESAB reports bond strengths about 145 psi (1 MPa) to granite for steel fiber reinforcshotcrete placed by the wet process.20 A bond strength ofabout 0.04 fc′

* (540 psi, 3.7 MPa) was reported for in stests at the Peachtree Center Station, Atlanta, subwayrough-surfaced granitic gneiss. These values were obtaby pulling off a 2 x 2-ft (610 x 610-mm) steel plate embedded in a flat (not arched) shotcrete layer and calculatingbond strength.21 This is compared to 0.1 fc′ (135 psi, 0.9MPa) for similar laboratory tests.21 In other tests, a core driwas used to isolate a cylindrical specimen that was pulled from the rock. Here, tensile bond strengths of 0.02 fc′(130 psi, 0.9 MPa) were obtained for fiber reinforced shcrete compared to 0.03 to 0.05 fc′ (220 to 375 psi, 1.5 to 2.MPa) for plain shotcrete.21

2.4—Mix compositions2.4.1 General—Most steel fiber reinforced shotcre

placed to date has used the dry process. Early applicaused a fine aggregate mix having a sand:cement ratio of by weight or about 940 lb of cement per yd3 (560 kg/m). Mixes

* fc′ here is the compressive strength of the concrete as tested.

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containing 3/8 and 3/4-in. (9 and 19-mm) aggregate and lesscement have been used more recently, and this has helped reduce shrinkage. The amount of fiber has varied from abou0.5 percent by volume to about 2 percent by volume (66 to265 lb/yd3; 39 to 157 kg/m). The proportions of typical mixesare shown in Table 2.3.1. The fiber amounts shown in Table2.3.1 are before gunning. Since the fiber rebound is generallygreater than the aggregate rebound, there is usually a smallepercentage of fiber in the applied shotcrete.11

2.4.2 Fiber size considerations—Most fibers used inshotcrete mixes are about 3/4 to 11/4-in. long (19 to 32-mm).While both shorter, 1/2 in. (13 mm) and longer fibers, up to11/2 to 2 in. (38 to 50 mm), have been used; the midrange ofabout 1 in. (25 mm) has become the preferred length fromthe standpoint of in-place shotcrete strength and ease of mixing and placing. Shorter fibers are easier to mix and shooand they rebound less, but the shotcrete properties, particularly toughness and post-crack resistance, are lower. Longefibers, although superior in producing strength and tough-ness properties, usually result in more plugging and have ahigher fiber rebound rate. Some of these disadvantages withshorter fibers have been overcome with the introduction offibers having deformations or end anchorage provisions.

2.5—Batching and mixing2.5.1 General—Batching and mixing for the dry process

is often done by mixing the dry ingredients, complete with fi-bers, in a transit mixer. This is then delivered to the hopper(gun) of the shotcrete machine. The material has also beemixed the same as normal shotcrete with the fibers beingadded to a mixing hopper by a screw auger or in a separatair stream. Fiber feeders, nozzles with the provision for fiberaddition, and special mixers are also available (Section2.6.2). Prebagging has been found to be very useful, particularly in mines where a mixer and bulk materials wouldaggravate space problems. Batching and mixing of steel fi-ber reinforced mixes with loose, bulk fibers need some careto avoid the formation of fiber balls.

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2.5.2 Dry-mix —Good results were obtained in a turbinemixer (a stationary, cylindrical, flat-bottomed pan with re-volving mixing arms) for U.S. Bureau of Mines tests. Thesand was placed in the mixer first, and the fibers were addethrough a 21/2-in. (63-mm) mesh screen to break up any fiberclumps. After transfer to a transit mixer and transport to a remote job site, the cement was added from sacks. A screeover the machine hopper, already a part of the equipmenwas used to intercept any fiber balls that were formed.

506.1R-5COMMITTEE REPORT ON FIBER REINFORCED SHOTCRETE

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2.6.2 Equipment—Existing shotcrete equipment has beeused to apply steel fiber reinforced shotcrete with little or modifications. The modifications, when made, are generato reduce plugging by eliminating restrictions such as 90-delbows or abrupt changes in hose size. If line size is reduca long, tapered reducer should be used. When pluggingcurs, it is usually at the outlet from the gun where a suddsize reduction or change in direction is a common featuLarger hose sizes, 2 in. (50 mm) in diameter and up, wbetter. Generally, the hose diameter should be a minimumtwo times the fiber length. However, 1-in. (25-mm) fiber habeen gunned through 1- in. (25-mm) hose, and fiber reforced refractories using 1-in. (25-mm) fiber are shot reglarly through 11/2-in. (38-mm) hose.

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For a larger project, the Snake River rock slope stabilition, the contractor charged the materials in 5 yd3 (3.8 m3)batches into a large hopper using a front-end loader and fthere into transit mixers via a conveyor. The ingredienwere added in the following order: all the sand; one-halfthe fibers; all the cement plus the accelerator; and one-hathe fibers. This technique, where 500 lb (225 kg) of loobulk fibers were added at one time, would normally woonly for short fibers with a low aspect ratio such as thoused on this project—1/2 x 0.010-in. (13 x 0.25-mm) fibers withan aspect ratio of 50. Fibers were added through a 4 x 4- in.(100 x 100-mm) crusher screen.

The important parts of the batching and mixing proceduthat differ from mixing plain shotcrete are:

1) Fibers that show a tendency to clump should be adthrough a screen or by a shaker or apparatus that sepathem and adds them so that they do not reclump. This meadding them to a rotating mixer, a conveyor belt, or a scrconveyor that is carrying the fibers away fast enough so the fibers do not stack up on each other.

2) Mixing should avoid bending the fibers. Badly bent fbers cause poor compaction and reduced strengths. A pa(pugmill) mixer with small counter-rotating paddle wheehas caused severe bending and subsequent formation of balls.12

3) A screen should be put over the shotcrete hopper tovert any fiber clumps.

Williamson22 reported that a screw-type mixer-conveyowas used along with a metering fiber feeder to mix shotcrfor spraying experimental domes at Champaign, Ill., by tU.S. Army Corps of Engineers. The fibers were mixed in tscrew conveyor and the mix discharged directly into the ghopper. The U.S. Bureau of Mines has also added the fibto a screw conveyor prior to discharging into the gun hopon a rotating barrel-type shotcrete machine.

It has been found that a good electrical ground to the gand nozzle dramatically reduces the fiber clumping aplugging that might otherwise occur.

Collated fibers, bundled together with a quick-dissolvinglue, are available for the dry-mix process. They are addirectly to the mixer after the aggregate has been addThey come apart after addition of the water at or near nozzle.

2.5.3 Wet-mix—Wet-mix shotcrete uses a wet mix simlar to that used for cast-in-place concrete applications. Texperience gained from mixing steel fiber reinforced cocrete for cast-in-place applications may be used to help baand mix fiber reinforced mixes for wet shotcreting. (See A544.1R—Chapter 3, “Preparation of Fiber Reinforced Cocrete.”)

There are some precautions that should be taken to prethe formation of fiber balls when adding loose bulk fibers the wet-mix. The fibers should not be added too quickThey should be added clump-free and should be carried abefore they pile up on one another. It may be necessarpass them through a screen or shaker screen. They shoulbe allowed to hang up or pile up on their way to or inside

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mixer. A good method is to introduce the fibers to the fine agregate on a conveyor belt during the addition of aggrega

Where fibers are added directly to a transit mixer, thebers should land on the mix, not on the mixing vanes whthey can form clumps. The drum must rotate fast enoughcarry away the fibers as they enter the mix.

Collated fibers, fibers with a very low aspect ratio (usualess than about 40) and some large diameter fibers maadded directly into a completed mix without causing clumping problem. Over-mixing should be avoided, in aevent, as too much mixing of these or any fiber may resulfiber ball formation. Worn mixing blades or harsh mixemay also result in fiber balls. Therefore, a screen shouldput over the pump hopper to intercept fiber balls.

2.6—Installation 2.6.1 General—Applying steel fiber reinforced shotcrete

is basically the same as applying plain shotcrete. Informaton good application techniques is included in ACI 506.R.Specification requirements suitable for use in contracts included in ACI 506.2.

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Other modifications have included: removing elastomeic wear linings at elbows, adding vibrators or revolvinwiper arms to the hopper screen, and adding vanes inhopper or changing the wheel size on segmented rotor types to speed up material delivery. Sometimes a stronrotor motor is needed. If no hopper screen is present, should be added to divert fiber clumps that would othewise plug the gun. Fig. 2.6.2.1 shows modifications madeto a gun hopper for the Snake River rock slope stabilizatproject.15,23

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Fiber reinforced shotcrete has been successfully appwith every kind of delivery equipment, from the original single or dual chamber feed wheel type to the more recentvolving barrel and segmented rotor types now in commuse. It has been placed by wet-mix using a pressurized chber-type machine, squeeze-pump-type pumps, and posdisplacement pumps.

Some special equipment has been devised to separatemeter steel fibers in a separate air stream and add them anozzle for both wet- and dry-mix. This equipment enabthe use of high aspect ratio fibers (up to about 125), avo

506.1R-6 ACI COMMITTEE REPORT

Fig. 2.6.2.1—Modified gun hopper with screen, revolving arms, and pneumatic vibrator.

putting the fibers through the gun, and eliminates the fibeballing problem.

Specialized equipment is available for feeding steel fi-bers separately to the dry-mix shotcrete mix or for feedingprefibrated mixes to the gun. Fig. 2.6.2.2 and 2.6.2.3 showexamples.

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Fig. 2.6.2.2—Integrated fiber feeder, mixer, and gun for steel fiber reinforced shotcrete.

Fig. 2.6.2.3—Predampening and mixing unit with fiber feeder for refractory shotcrete.

2.6.3 Rebound considerations2.6.3.1 General—The factors affecting rebound encom

pass a wide range of items and conditions. Generally, it been noted that a greater percentage of fibers than aggrerebound from the wall. Ryan24 reports fiber retention of 40percent overhead and 65 percent on vertical surfacParker12 reported fiber retention of 44 to 88 percent (avera62 percent) for coarse aggregate mixes gunned onto verpanels. In the Atlanta Research Chamber tests, the averebound in a 10-min test where 2500 lb (1130 kg) of mix wshot was 22 percent for a 3-in.-(75-mm)-thick placemeThe fiber content before gunning was 3.3 percent by weiof the dry material, while the fiber content in the reboumaterial was 4.6 percent.21

Some investigators and applicators have reported that sfiber reinforced shotcrete showed less total rebound th

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plain shotcrete. Others have reported no difference from thefiber mixes.

An example of less rebound was reported for a trial in Ne-vada conducted by Fenix and Scisson, Inc. In that work, 4 yd3

(3 m3) of a steel fiber mix consisting of 700 lb (317 kg) ce-ment, 2700 lb (1225 kg) sand, and 150 lb (68 kg) 1/2 x 0.010-in.(13 x 0.25-mm) fiber per yd placed 6-in. (150-mm) thick hada total estimated rebound of 10 percent. A control batch ap-plied under identical conditions by the same personnel had anestimated rebound of 31 percent. The work was done in a tun-nel and included vertical and overhead surfaces.15

On the other hand, Parker12 reported average rebounds of18.3 and 17.7 percent for a nonfiber mix and a fiber mix, re-spectively, and concluded from that and other data that themere presence of fibers in a mix does not affect rebound ap-preciably. Instead, other factors appear to be more importantthan fiber.

Reference 4 states:

“Due to rebound, the effective amount of fibers is reduced to aboutonly 50 to 70 percent of the amount in the mix in dry-mix shotcrete.For wet-mix shotcrete, the amount of fiber rebound is approximately5 to 10 percent.”

2.6.3.2 Factors affecting rebound of fibers—Quantita-tive data on rebound of steel fiber reinforced shotcrete withthe dry-mix process were obtained in a study that systemati-cally investigated variables one at a time and usedhigh-speed photography to observe the shotcrete airstream.12

The photography showed that many of the steel fiberswere in the outer portion of the airstream and that many ofthem were blown away radially from near the point of in-tended impact shortly before or after they hit. Some fiberswere blown up into the air and floated down. It was obviousthat the fibers were mostly blown away by the remnant aircurrents and that the effect was not one of the fibers simplybouncing off the surface. If lower air pressure or less air isused, the amount and velocity of the remnant air currents isless and the rebound of fiber is correspondingly less.

Reference 19 presents data on the effect of five steel fibergeometries on rebound and other shotcrete characteristics. Itshows ranges of fiber rebound of:

• dry-mix 35 to 78 percent

• wet-mix 12 to 18 percent

506.1R-7R REINFORCED SHOTCRETE

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COMMITTEE REPORT ON FIBE

2.6.3.3 Conditions that reduce rebound—Parker’sstudy12 concluded that the rebound process differed durinestablishment of an initial critical thickness (Phase 1) ansubsequent gunning into fresh shotcrete (Phase 2).

During Phase 1, anything that promotes adherence of mterial on the wall should reduce rebound. This includes thfollowing mix conditions: a higher cement content; morefines in the mix (fly ash or very fine sand); smaller maximumsize aggregate; proper wetness of aggregates so that partare well-coated with cement; and a finer gradation.

After the initial critical thickness is established, Phase rebound is reduced by any condition or set of conditions thmakes the shotcrete on the wall softer or more plastic, at leuntil it tends to drop off. Thus, for maximum reduction oPhase 2 rebound, shotcreting as wet as possible, that is,wettest stable consistency, is one of the most beneficial aeasiest conditions to control.

A large number of measures can be used to reduce reboof steel fiber reinforced shotcrete in dry-mix. The most efective of these measures (which also applies to plain shcrete) seems to be reduction of the air pressure, air velocor amount of air at the nozzle; use of more fines and smalaggregate; use of shorter, thicker fibers; predampening to the right moisture content; and shotcreting at the wettest sble consistency.12,15

2.7—Applications Applications of fiber reinforced shotcrete have been mad

to rock slopes, mines, tunnels, dams, powerhouses, bridarches, thin shell dome structures, rock caverns for oil stoage, houses, boat hulls, landslides for stabilization, and deriorated concrete surfaces for repair.

2.7.1—Slope stabilization2.7.1.1 Corps of Engineers, Snake River rock slop

stabilization9,23—A large application of steel fiber rein-forced shotcrete was completed in January 1974, near LitGoose Dam along the Snake River in the State of Washinton. The shotcrete was used to stabilize a deteriorating stion of rock slope above the Camas Prairie Railroad. Thwork included scaling, installing rock bolts, and applyingshotcrete a minimum of 21/2-in. thick (63-mm). The area in-volved was about 1550-ft (460-m) long and varied from 1to 45-ft (5 to 14-m) high for a total of 6900 yd2 (5800 m2).

2.7.1.2 Joint Nordic Program (Nordforsk), oil refinery,Brofjorden, Sweden25—A large application was also made aan oil refinery at Brofjorden, on the west coast of Swede(Fig. 2.7.1.2).

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About 5380 yd2 (4500 m2) of rock surface was stabilized.A layered construction was used: 1/4 to 3/8 in. (5 to 10 mm)of plain shotcrete followed by 13/16 in. (30 mm) of steel fi-ber reinforced shotcrete covered with a top layer of 1/4 to 3/

8 in. (5 to 10 mm) of plain shotcrete.2.7.2—Selected underground applications

2.7.2.1 Corps of Engineers, Ririe Dam, tunnel adit,Idaho3—In December 1972, steel fiber reinforced shotcretwas used to line a 40 ft (12 m) length of an exploratory tunn

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adit on the right abutment of Ririe Dam, Idaho. Thicknewas 3 in. (75 mm) and the 34-day flexural strength of cbeams was 910 psi (6.3 MPa) (ASTM C 78 test method). Tlining survived a blasting operation with minor cracking.

2.7.2.2 British Columbia Hydro-Peace River Site Ctunnels26—At the Site C Project, a proposed earthfill daand powerhouse on the Peace River in northeastern BrColumbia, steel fiber reinforced dry-mix shotcrete was usto line several hundred feet of exploratory tunnels and a chamber. These fibers replaced the originally designed wmesh. The work was done in 1981 and 1982.

A thickness of 2 in. (50 mm) was specified. The shotcrused was a premixed type supplied in bags. The avercomposition of this mix is given in Table 2.7.2.2.

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2.7.2.3 Atlanta subway tunnel lining21—Another tunnelapplication, of limited size, was made in the MetropolitanAtlanta Rapid Transit Authority (MARTA) subway. Here, a200-ft (61-m) length of the subway tunnel was lined with 4to 6 in. (100 to 150 mm) of steel fiber reinforced shotcrete bthe dry-mix process. Examination after 18 months of usshowed the lining to be in satisfactory condition.

2.7.2.4 U.S. Bureau of Mines, coal mine applications—Underground rooms at the U.S. Bureau of Mines’ experimental mine at Bruceton, Pa., were enlarged, rock boltedand lined with steel fiber reinforced shotcrete.27 Fiber shot-crete was also used to coat bulkheads, seals, and stoppinformed by Bernold steel.28

Shotcrete has been shown by testing to provide good fireproofing protection for urethane foam.29

2.7.2.5 Bolidens Gruv AB, mines and ore shaft,Sweden20—Steel fiber reinforced shotcrete has been used ia number of mines in Sweden. At the Bolidens Gruv ABmine near Kristineberg, the material was used to line and stbilize a gravity ore transfer shaft that was deteriorating fromthe impact of the ore. The shaft was filled with ore so that thtop surface of the ore became the working platform for thshotcreting operation (Fig. 2.7.2.5).

506.1R-8 ACI COMMITTEE REPORT

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Component lb/yd3 kg/m3

Type 10 cement 740 439

10-mm aggregate 610 362

Concrete sand 1927 1143

Fine blend sand 376 223

3653 2167

Steel fibers 100 59

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The thickness varied from 4.0 to 20 in. (100 to 500 mm

2.7.2.6 British Rail, arch and tunnel relining, England—Steel fiber reinforced shotcrete was used strengthening tunnels and brick arches under bridgesBritish Rail in England. It is applied up to 6-in. (150-mmthick. A 1/2-in. (13-mm) flash coat is used to cover exposfibers (Fig. 2.7.2.6). One advantage found in the use of fibreinforced shotcrete in rail tunnel work is that the scaffoldrequired for mesh installation can be eliminated and trainterruption is minimized.

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ag-Fig. 2.7.2.6—Brick railway bridge near Birmingham, England; reinforced with about 6 in. (150 mm) of steel fiber reinforced shotcrete.

2.7.2.7 Swedish State Power Board, Ringhals NuclePower Station—An emergency cold water tunnel at the Ringhals Nuclear Power Station in Sweden was lined with sfiber reinforced shotcrete using the wet process equipmIt was used in conjunction with rock bolts (Fig. 2.7.2.7).

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Fig. 2.7.2.7—Emergency cold water tunnel lining at Ringhals Nuclear Power Station, Sweden.

2.7.2.8 Roadway tunnels, Japan—The Japanese haveused steel fiber reinforced shotcrete in at least three vehiclar tunnels. In the Miyanoshita Tunnel, it was used to repaconcrete lining damaged by rock pressure. In the Itaya Tunel, it was placed 4-in. (100-mm) thick to repair the origina50-year-old lining that had deteriorated from icing conditions. In a tunnel near Hakodate, Hokkaido, it was placed a trial lining. All of these applications used the wet-mix ana squeeze-type pump.

2.7.3 Dome structures—Two construction methods havebeen used to build dome-shaped structures using steel fireinforced shotcrete. In the first method, polyurethane foais sprayed on the underside of an inflatable membrane of desired shape (from inside the inflated shape) to a thickneof about 4 in. (100 mm).30,31 After the foam hardens, theshotcrete is applied to the underside of the foam 11/2 to 3-in.(38 to 76-mm) thick or more. The resulting structure is very efficient thermally and can support heavy roof loads, comparto conventional structures.32 Uses are for homes, offices,warehouses and the storage of grain, potatoes, and otherricultural products.

The second construction method reverses the foam ashotcrete so that the shotcrete is on the outside. Smdomes of this type were made as experimental shelters protection against small fire arms and grenades.22

2.7.4 Other applications—Other steel fiber reinforcedshotcrete applications have included lining of an oil storagcavern at Skarvik, Sweden, using the wet process; residen

506.1R-9COMMITTEE REPORT ON FIBER REINFORCED SHOTCRETE

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of sandwich wall construction at Rainworth, England; lighhouse and chimney repairs in Sweden; resurfacing of a roflame deflector at Cape Canaveral, Fla.; coal mine strenening and sealing of stoppings by National Coal Board, Egland; stabilization of the Tuve landslide in Sweden; aforming boat hulls similar to ferrocement, using fibers afibers plus mesh.

2.8—Available design information2.8.1 General—Design of steel fiber reinforced shotcret

for structural uses is similar to design of plain shotcrete. though design with fiber reinforced shotcrete and convtional shotcrete is basically the same, the material propecan be significantly different, thereby allowing considerabdifference in shotcrete thickness and amount of reinforment. At present, limited data are available for the designfiber reinforced shotcrete structures. Most design data are available are for ground support such as tunnel lining

Shotcrete in ground support has been most successftreating problems associated with loosening ground andslaking.

At present, the design of thin shotcrete linings is basedempirical rules and/or analytical models of shotcrete-robehavior. Empirical design is based on actual tunnel expence. The analytical models have been developed fromservation of shotcrete performance under service conditiand from large scale testing in the laboratory and in the fie

2.8.2 Precautions—The scope of this report prevents detailed treatment of the design of shotcrete for ground sport. However, it is appropriate to list some available refences relating to design and engineering propertiesshotcrete and to list some general precautions.

Shotcrete may be used as sole support of undergroundcavations but only in cases where a good shotcrete-rbond can be obtained, when the shotcrete is thick enougact as a structurally continuous lining, or when air slakingthe only ground problem. In any other cases, shotcrshould be employed together with some other support ments (i.e., rock bolts, steel ribs, etc.).

The prevention or reduction of water flow from the groubecause of the sealing action of the shotcrete may leadbuildup of hydraulic forces and possibly to stability prolems in the ground. Therefore, it is advisable to provide drainage of such water.

A thin shotcrete lining applied over irregular rock surfachas been found to be inadequate as the sole support of uground excavations in the following cases:11

1. Drill and blast openings 20 ft (6.1 m) or more in diameter.

2. Zones where blocks are bounded by smooth to slickjoint surfaces, the overbreak is prominent, and blocksizes are typically 4 ft (1.2 m) or more in width.

3. Vertical side walls more than 10 ft (3 m) in height.

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2.8.3 Empirical design, plain shotcrete—Several differ-ent empirical rules for estimating shotcrete thicknesses tunnel support are presented in a publication by Mahar11

These rules include tables of thicknesses based on chistories in which shotcrete did or did not fail. Various thicknesses, depending on conditions, were formulated by berts,33 Kobler,34 Cecil,35 and Heuer.36 Other researcherswho used rock quality designation (RQD) and rock structurating (RSR) to refine empirical rules include Deere37 andWickham.38

2.8.4 Design based on analytical models, plain shot-crete—A second method of estimating shotcrete thicknefor initial support involves use of analytical models of shocrete behavior.

A suggested method of determination of shotcrete thicness for a flat-roof tunnel by using models and analysesshown in Mahar11 and Cecil.35 A thickness of not less than 2in. (50 mm) is used because of possible deterioration of thner layers from shrinkage, cracking, construction activity, water seepage.

Design of shotcrete as a circular ring following the ultmate strength concepts of reinforced concrete design is illtrated by Peng.39 Rabcewitz’s methods, widely used in theNew Austrian Tunnelling Method, are illustrated in a serieof articles.40,41

2.8.5 Analytical models based on laboratory and fieldtests, fiber reinforced shotcrete—Analytical models forsteel fiber reinforced shotcrete based on large scale laborry tests were formulated by Fernandez-Delgado of the Uversity of Illinois and published in ACI SP-54.42 Additionaldata on the same general subject (i.e., adhesion, flexure,punch loads in arched and flat configurations for steel fibreinforced shotcrete) also appear in ACI SP-54.43

The work was continued in large scale field tests in the Alanta Research Chamber, and the results were applied todesign of liners for underground openings.44 The models in-clude analysis for wedges displacing through the liner athrust coefficients for analysis of thicker, continuous arcconfigurations.

2.8.6 Additional data, fiber shotcrete—Data on the per-formance and design of steel fiber reinforced shotcrete copared to mesh reinforced shotcrete anchored on 4-ft (1.2centers is given in a report by Morgan.45 The report indicatesthat the two cases are equivalent and that fiber reinforcshotcrete provided good residual load capacity with large dformations, i.e., 2 in. (50 mm). Additionally, tests madby British Columbia Hydro on the proposed Site C projeon the Peace River confirm that in similar tests on meand fiber reinforced panels, first and second cracks genally occur at higher loads in the steel fiber reinforced shot-crete than in the mesh reinforced shotcrete. After crackinboth types exhibited similar load-carrying capabilities.26

Additional data on engineering properties were generateby Poad, Serbousek, and Goris.8

506.1R-10 ACI COMMITTEE REPORT

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CHAPTER 3—SYNTHETIC FIBER REINFORCED SHOTCRETE

3.1—Polypropylene fiber rein forced shotcrete3.1.1 Types of fibers—Polypropylene fibers that have

been used in shotcrete range typically from 1/2 to 2 in. (12 to50 mm) and may be straight or of a fibrillated configuration

3.1.2 Production aspects—The methods of addingpolypropylene fibers to a mix are similar to those for steefibers described in Section 2.5. Generally, they do not havethe same susceptibility to clumping as steel fibers. However, balling may be experienced at larger addition rates suas 10 to 12 lb/yd3 (6 to 7 kg/m3).

In terms of addition rates, typical values have about 1.lb/yd3 (0.9 kg/m3), which is approximately 0.1 percent byvolume. However, some applications have used up t10 lb/yd3 (6 kg/m3) to achieve improved performance.

3.1.3 Properties—It is generally recognized that polypro-pylene fibers will affect shotcrete properties in a mannesimilar to steel fibers—see Section 2.3—but not to the samedegree.

Reference 19 states that, at normal addition rates of 1 to 2kg/m3 (1.7 to 3.4 lb/yd3):

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“Synthetic fibers contribute to the stability of shotcrete material hav-ing excessively low mechanical properties by modifying rheologicalbehavior of the fresh concrete and of the concrete during hardenin(improved cohesion and shearing resistance). Contributions to improve the hardened properties are negligible.”

However, tests at higher addition rates show improvproperties.

3.2—Shotcrete using other synthetic fibe rsThere are limited data available on the use of other s

thetic fibers in shotcrete.

CHAPTER 4—REFERENCES

4.1—Specified and/or recommended references The documents of the various standards-producing org

zations referred to in this document are listed below wtheir serial designation.

American Concrete Institute (ACI)544.1R State-of-the-Art Report on Fiber Reinforced

Concrete544.2R Measurement of Properties of Fiber Reinforced

Concrete506.R Guide for Shotcreting506.2 Specification for Materials, Proportioning, and

Application of Shotcrete547R State-of-the-Art Report on Refractory Concrete

American Society of Testing and Materials (ASTM)A 820 Steel Fiber for Fiber Reinforced ConcreteC 78 Flexural Strength of Concrete (Using Simple Bea

with Third-Point Loading)C 900 Test Method for Pullout Strength of Hardened

Concrete

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C 1018 Test Method for Flexural Toughness and FirstCrack Strength of Fiber Reinforced Concrete

C 1116 Specification for Fiber Reinforced Concrete andShotcrete

The above publications may be obtained from the follow-ing organizations:

American Concrete InstituteP.O. Box 9094Farmington Hills, MI48333-9094

American Society for Testing and Materials100 Barr Harbor DriveWest Conshohocken, PA19428

4.2—Cited references1. Forrest, M. P.; Morgan, D. R.; Obermeyer, J. R.; Parker, P.; and La

Moreaux, D. D., “Seismic Retrofit Little Rock Dam,” Concrete Interna-tional, V. 17, No. 11, Nov. 1995, pp. 30-36.

2. Zollo, R. F., “Collated Fibrillated Polypropylene Fibers in FRC,” SP-81, Fiber Reinforced Concrete—International Symposium, American Con-crete Institute, Farmington Hills, Mich., 1984, pp. 397-409.

3. Malhotra, V. M.; Carette, G. G.; and Bilodeau, A., “Mechanical Prop-erties and Durability of Polypropylene Fiber Reinforced High-Volume FlyAsh Concrete for Shotcrete Application,” ACI Materials Journal, V. 91,No. 5, Sept.-Oct. 1994.

4. Krentz, G. W., “Selected Pneumatic Gunites for Use in UndergroundMining: A Comparative Engineering Analysis,” Bureau of Mines Circular1C 8984, U.S. Department of the Interior, 1984.

5. International Tunnelling Association, Shotcrete for Rock Support;Guidelines and Recommendations, Swedish Rock Engineering ResearchFoundation (Be Fo), Stockholm, 1992.

6. Lankard, D. R., “Field Experiences with Steel Fibrous Concrete,” pre-sented at American Ceramic Society Meeting, Chicago, Apr. 26, 1971.

7. Parker, H. W., “Current Field Research Program on Shotcrete,” Pro-ceedings, Use of Shotcrete for Underground Support, Eng. Fnd., ASCE SP-45, 1974, pp. 330-350.

8. Poad, M. E.; Serbousek, M. O.; and Goris, J., “Engineering Proper-ties of Fiber-Reinforced and Polymer-Impregnated Shotcrete,” Report ofInvestigations No. 8001, U.S. Bureau of Mines, Washington, D.C., 1975,25 pp.

9. Kaden, R. A., “Fiber Reinforced Shotcrete: Ririe Dam and LittleGoose (CPRR) Relocation,” SP-54, Shotcrete for Ground Support, Ameri-can Concrete Institute/American Society of Civil Engineers, FarmingtonHills, Mich., 1977, pp. 66-88.

10. Hannant, D. J., Fiber Cements and Fiber Concretes, John Wiley &Sons, New York, 1978, 219 pp.

11. Mahar, J. W.; Parker, H. W.; and Wuellner, W. W., “Shotcrete Prac-tice in Underground Construction,” Report No. FRA-OR&D 75-90, Fed-eral Railroad Administration, Washington, D.C., Aug. 1975, 482 pp.

12. Parker, H. W.; Fernandez, G.; and Lorig, L. J., “Field-Oriented Inves-tigation of Conventional and Experimental Shotcrete for Tunnels,” ReportNo. FRA-OR&D 76-06, Federal Railroad Administration, Washington,D.C., Aug. 1975, 628 pp.

13. Lankard, D. R., “Steel Fiber Reinforced Refractory Concrete,” SP-57, Refractory Concrete, American Concrete Institute, Farmington Hills,Mich., 1978, pp. 241-263.

14. Glassgold, I. L., “Refractory Shotcrete—Current State of the Art,”Concrete International: Design & Construction, V. 3, No. 1, Jan. 1981, pp.41-49.

15. Henager, C. H., “The Technology and Uses of Steel Fibrous Shotcrete:A State-of-the-Art Report,” Battelle-Northwest, Richland, Sept. 1977, 60 pp.

16. Henager, C. H., “A New Wrinkle—Shotcrete Containing Steel

506.1R-11COMMITTEE REPORT ON FIBER REINFORCED SHOTCRETE

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19. Banthier, N.; Trottier, J.-F.; Beaupre, D.; and Wood, D., “Steel FReinforced Shotcrete: Influence of Fiber Geometry,” Third Canadian Symposium on Cement and Concrete, Ottawa, 1993.

Fibers,” Concrete Construction, V. 20, No. 8, Aug. 1975, pp. 345-347. 17. Morgan, D. R., “Steel Fiber Shotcrete—A Laboratory Study,” Con-

crete International: Design & Construction, V. 3, No. 1, Jan. 1981, pp70-74.

18. Ramakrishnan, V.; Coyle, W. V.; Dahl, L. F.; and Schrader, E. K.,Comparative Evaluation of Fiber Shotcretes,” Concrete International:Design & Construction, V. 3, No. 1, Jan. 1981, pp. 59-69.

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20. Sandell, B., “Steel Fiber Reinforced Shotcrete (StalfiberarmeSprutbeton),” Proceedings, Informations-Dagen 1977, Cement-Och Betoginstitutet, Stockholm, 1977, pp. 50-75.

21. Rose, D. C., et al., “The Atlanta Research Chamber, AppResearch for Tunnels,” Report No. UMTA-GA-06-0007-81-1, U.S. Depart-ment of Transportation, Washington, D.C., Mar. 1981.

22. Williamson, G. R., et. al., “Inflation/Foam/Shotcrete System Rapid Shelter Construction,” CERL Technical Report No. M-215, U.S.Army Construction Engineering Research Laboratory, Champaign, May 1977.

23. Kaden, R. A., “Slope Stabilized with Steel Fibrous Shotcrete,” West-ern Construction, Apr. 1974, pp. 30-33.

24. Ryan, T. F., “Steel Fibers in Gunite, An Appraisal,” Tunnels andTunnelling (London), July 1975, pp. 74-75.

25. Malmberg, B., and Ostfjord, S., “Field Test of Steel Fiber ReinforcShotcrete at Scan-Raff, Brofjorden,” Fiberbetong, Norforsks Projekt Com-mittee for FRC-Material Delvapporter, Cement-Och Betonginstitutet,Stockholm, 1977, pp. Y1-Y16.

26. “Peace River Development Site C Project, Shotcrete TestinHydroelectric Generation Projects Division, Geotechnical Department,British Columbia Hydro, Jan. 1983.

27. Chronis, N. P., “Three Innovations in Mine Expansion Tested at Bceton Experimental Mine,” Coal Age, V. 80, No. 4, Apr. 1975.

28. Murphy, E. M., “Steel Fiber Shotcrete in Mines,” Concrete Con-struction, V. 20, No. 10, Oct. 1975, pp. 443-445.

29. Warner, B. L., “Evaluation of Materials for Protecting Existing Urthane Foam in Mines,” Report No. ORF 75-76 (NTIS PB 254 682), U.SBureau of Mines, Washington, D.C., Sept. 1974.

30. Wilkinson, B. M., “Foam Domes, High Performance EnvironmenEnclosures,” Concrete Construction, V. 23, No. 7, July 1978, pp. 405-406.

31. “Shotcrete and Foam Insulation Shaped Over Inflated BalloForm,” Concrete Construction, V. 27, No. 6, June 1982, pp. 511-513.

32. Nelson, K. O., and Henager, C. H., “Analysis of Shotcrete DomLoaded by Deadweight,” Preprint No. 81-512, ASCE Convention (St.Louis, Oct. 1981), American Society of Civil Engineers, New York, 1981

33. Alberts, C., “Bergforstarkning genom Beton sprutning och Injecting,” Proceedings, 1965 Rock Mechanics Symposium, Publication N142, Swedish Academy of Sciences, Stockholm, 1965.

34. Kobler, H. G., “Dry-Mix Coarse-Aggregate Shotcrete as Undground Support,” SP-14, Shotcreting, T. J. Reading, ed., American Concrete Institute, Farmington Hills, Mich., 1966, pp. 33-58.

35. Cecil, O. S., “Correlations of Rock Bolt-Shotcrete Support and RQuality Parameters in Scandinavian Tunnels,” PhD thesis, UniversityIllinois, Urbana, 1970.

36. Heuer, R. E., “Selection/Design of Shotcrete for Temporary Sport,” SP-45, Use of Shotcrete for Underground Structural Support, Amer-ican Concrete Institute/American Society of Civil Engineers, FarmingHills, Mich. 1974, pp. 160-174.

37. Deere, E. U.; Peck, R. B.; Monsees, N. E.; and Schmidt, B., “Deof Tunnel Liners and Support Systems,” Contract No. 3-0152 (NTIS 183 799), Office of High Speed Ground Transportation, U.S. Departmof Transportation, Washington, D.C., 1969, pp. 387-391.

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38. Wickham, G. E.; Tiedemann, H. R.; and Skinner, E. H., “GroundSupport Prediction Model RSR Concept,” Proceedings, North AmericanRapid Excavation and Tunnelling Conference, American Institute of Min-ing, Metallurgical, and Petroleum Engineers, New York, V. 1, 1974, pp.691-707.

39. Peng, S. S., Coal Mine Ground Control, John Wiley & Sons, NewYork, 1978, pp. 415-416.

40. Rabcewicz, L., “The New Austrian Tunnelling Method, Parts I, II,III,” Water Power (London), Nov.-Dec. 1964, and Jan. 1965.

41. Rabcewicz, L., “Stability of Tunnels under Rock Loads, Parts I, II,III,” Water Power (London), June 1969, pp. 225-234, July 1969, pp.266-273, and Aug. 1969, pp. 297-302.

42. Fernandez-Delgado, G.; Mahar, J. W.; and Parker, H. W., “StructuralBehavior of Thin Shotcrete Liners Obtained from Large Scale Tests,” SP-54, Shotcrete for Ground Support, American Concrete Institute/AmericanSociety of Civil Engineers, Farmington Hills, Mich., 1977, pp. 399-442.

43. Holmgren, J., “Thin Shotcrete Layers Subjected to Punch Loads,”SP-54, Shotcrete for Ground Support, American Concrete Institute/Ameri-can Society of Civil Engineers, Farmington Hills, Mich., 1977, pp.443-459.

44. Fernandez-Delgado, G., et al., “Thin Shotcrete Linings in LooseningRock,” The Atlanta Research Chamber, Report No. UMTA-GA-06-0007-81-1,U.S. Department of Transportation, Washington, D.C., Mar. 1981.

45. Morgan, D. R., “Report on Steel Fiber Shotcrete for Tunnel SupportLining,” Hardy Associates Ltd., Vancouver, Mar. 1981.

4.3—General referencesArmelin, H. S., and Paula, H., 1995. “Physical and Mechanical Proper-

ties of Steel Fiber Reinforced Dry-Mix Shotcrete,” ACI Materials Journal,V. 92, No. 3, May-June.

Banthia, N.; Trottier, J.-F.; and Beaupre, D., 1994. “Steel-Fiber Rein-forced Wet-Mix Shotcrete: Comparison with Cast Concrete,” Journal ofMaterials in Civil Engineering, V. 6, No. 3.

Banthia, N.; Trottier, J.-F.; Beaupre, D.; and Wood, D., 1994. “Propertiesof Steel Fiber Reinforced Shotcrete,” CSCE Journal, V. 21, No. 4.

Banthia, N.; Trottier, J.-F.; Wood, D.F.; and Beaupre, D., 1992. “Influ-ence of Fiber Geometry in Steel Fiber Reinforced Dry-Mix Shotcrete,”Concrete International, V. 14, No. 5, May.

Frazen T., 1992. “Shotcrete for Underground Support: State-of-the-ArtReport with Focus on Steel-Fiber Reinforcement,” Tunnelling and SpaceAge Technology, V. 7, No. 4.

Henager, C. H., 1981. “Steel Fibrous Shotcrete: A Summary of the Stateof the Art,” Concrete International: Design & Construction, V. 3, No. 1,Jan., pp. 50-58.

Kirsten, H. A. D., 1993. “Equivalence of Mesh and Fiber Reinforced Shot-crete at Large Deflections,” Canadian Geotechnical Journal, V. 30, No. 3.

Morgan, D. R., 1991. “Steel Fiber Reinforced Shotcrete for Support ofUnderground Openings in Canada,” Concrete International, V. 13, No. 11,Nov.

Morgan, D. R.; McAshill, N.; Carette, G. C.; and Malhotra, V. M., 1992.“Evaluation of Polypropylene Fiber Reinforced High-Volume Fly AshShotcrete,” ACI Materials Journal, V. 89, No. 2, Mar.-Apr.

Smith, R. E.; Peerlmon, S. L. J.; and Wolosick, J. R., 1993. “Shotcretefor Underground Support,” Engineering Foundation, Niagara-on-the-Lake,Ontario, Canada, May.

Wallis, S., 1992. “Fibercrete at Cumberband Gap Advances NATM inthe U.S.,” Tunnels and Tunnelling, June.