Guide to Fiber-Reinforced Shotcrete

ACI 506.1R-08

Reported by ACI Committee 506

Guide to Fiber-Reinforced Shotcrete

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First PrintingNovember 2008

ISBN 978-0-87031-312-7

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ACI 506.1R-08 supersedes ACI 506.1R-98 and was adopted and publishedNovember 2008.

Copyright © 2008, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any

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506.1R-1

ACI Committee Reports, Guides, Manuals, StandardPractices, and Commentaries are intended for guidance inplanning, designing, executing, and inspecting construction.This document is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it contains.The American Concrete Institute disclaims any and allresponsibility for the stated principles. The Institute shall notbe liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.

Guide to Fiber-Reinforced ShotcreteReported by ACI Committee 506

ACI 506.1R-08

This guide describes the technology and applications of fiber-reinforcedshotcrete (FRS) using synthetic and steel fibers. Mechanical properties,particularly toughness, impact, and flexural strength, are improved by fiberaddition, and these improvements are described along with other typicalproperties and benefits, such as control of shrinkage cracking. Proportionsof typical mixtures, batching, mixing, and application procedures aredescribed, including methods of reducing rebound and equipment used toapply FRS. Applications of FRS are described, including rock-slope stabili-zation work, construction and repair of tunnel and mining linings, fireexplosive spalling-resistant linings, channel linings, pools and rockscapes,and structure repair. Available design information is briefly discussed, anddesign references are listed.

Keywords: fiber-reinforced shotcrete; fibers; linings; mining; repair; steelfibers; synthetic fibers; tunnels.

CONTENTSChapter 1—Introduction and scope, p. 506.1R-2

1.1—Introduction1.2—Scope1.3—Historical background

Chapter 2—Notation and definitions, p. 506.1R-2 2.1—Notation 2.2—Definitions

Chapter 3—Materials, p. 506.1R-23.1—General3.2—Fibers3.3—Other materials

Chapter 4—Mixture proportions, p. 506.1R-34.1—General4.2—Wet-process4.3—Dry-process

Jon B. Ardahl Jill E. Glassgold Jeffery L. Novak* Raymond C. Schallom, III*

Lars F. Balck, Jr. Charles S. Hanskat H. Celik Ozyildirim Raymond J. Schutz

Michael Ballou* Warren L. Harrison Harvey W. Parker Philip T. Seabrook

Nemkumar Banthia* Thomas Hennings* Ryan E. Poole W. L. Snow, Sr.

Chris D. Breeds Merlyn Isaak John H. Pye Curtis White

Patrick O. Bridger Marc Jolin James A. Ragland* Peter T. Yen

Wern-Ping “Nick” Chen Kristian Loevlie Venkataswamy Ramakrisnan George Yoggy*

Jean-François Dufour* Mark R. Lukkarila Michael Rispin Christopher M. Zynda

John R. Fichter Gregory McKinnon

*Subcommittee members who prepared this report.†Subcommittee Chair.

Peter C. Tatnall†

Chair

Lawrence J. TottenVice Chair

Dudley R. Morgan*

Secretary



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506.1R-2 ACI COMMITTEE REPORT

Chapter 5—Production, p. 506.1R-45.1—General5.2—Batching and mixing5.3—Application

Chapter 6—Test procedures, p. 506.1R-46.1—General6.2—Fresh properties6.3—Hardened properties

Chapter 7—Performance of fiber-reinforced shotcrete, p. 506.1R-6

7.1—Flexural strength7.2—Compressive strength7.3—Shear strength7.4—Bond strength7.5—Rebound considerations7.6—Shrinkage crack control7.7—Impact resistance7.8—Thermal explosive spalling

Chapter 8—Design considerations, p. 506.1R-88.1—General8.2—Empirical design8.3—Comparable moment capacity

Chapter 9—Specification and quality control considerations, p. 506.1R-9

9.1—General9.2—Performance specifications9.3—Prescriptive specifications

Chapter 10—Applications, p. 506.1R-910.1—General10.2—Ground support10.3—Rehabilitation and repair10.4—Architectural shotcrete10.5—Explosive spalling resistance

Chapter 11—References, p. 506.1R-1111.1—Referenced standards and reports11.2—Cited references

Appendix—Example of comparable moment capacity calculations, p. 506.1R-13

CHAPTER 1—INTRODUCTION AND SCOPE1.1—Introduction

Fiber-reinforced shotcrete (FRS) is mortar or concretecontaining discontinuous discrete fibers that is pneumaticallyprojected at high velocity onto a surface. Continuousmeshes, woven fabrics, and long rods are not considered asdiscrete fiber-type reinforcing elements in this guide.

1.2—ScopeThis document provides information on fiber-reinforced

shotcrete using synthetic and steel fibers. Topics coveredinclude materials used, mixture proportions, production ofshotcrete, testing procedures, performance of FRS, design

considerations (including an example in the Appendix),specifications, and some examples of applications.

1.3—Historical background FRS with steel fibers was first placed in North America

early in 1971 in experimental work directed by Lankard, etal. (1971). Steel FRS (SFRS) was proposed for undergroundsupport by Parker in 1971 (Parker 1974). Additional trialswere made by Poad in an investigation of new and improvedmethods of using shotcrete for underground support (Poad etal. 1975). Subsequently, the first practical applications ofSFRS were made in a tunnel adit at Ririe Dam, ID in 1973(Kaden 1977). Since that time, SFRS has been usedthroughout the world. Shotcrete using micropolypropylenefibers was first placed in Europe in 1968 (Hannant 1978).Macrosynthetic fibers for use in shotcrete were developed inthe mid-1990s and have been used in mining and slope stabi-lization projects (Morgan and Heere 2000).

CHAPTER 2—NOTATION AND DEFINITIONS2.1—NotationAS = area of conventional steel per unit widtha = AS fY /0.85fc′ b

b = unit width of sectiond = moment arm from loaded surface to center of

reinforcement= post-cracking residual flexural strength of a 4 in.

(100 mm) deep beam as determined at 0.02 in.(0.5 mm) deflection (Span/600) using ASTMC1609/C1609M

fY = yield strength of conventional reinforcementfc′ = compressive strength of shotcretet = FRS section thicknessφ = strength reduction factor, = 0.9 for flexure

2.2—Definitionsaspect ratio, fiber—the ratio of length to diameter of a

fiber in which the diameter may be an equivalent diameter.denier—measure of fiber diameter, taken as the mass in

grams of 9000 m (29,528 ft) of the fiber.equivalent diameter, fiber—diameter of a circle with an

area equal to the cross-sectional area of the fiber.macrofiber—a fiber with an equivalent diameter greater

than or equal to 0.012 in. (0.3 mm) for use in concrete.microfiber—a fiber with an equivalent diameter less than

0.012 in. (0.3 mm) for use in concrete.

CHAPTER 3—MATERIALS3.1—General

FRS is conventional shotcrete with fibers added. Materialsfor use in FRS should conform to the requirements of ASTMC1436, which covers the typical materials used in shotcrete,including chemical and mineral admixtures, fibers, and thecombined grading of aggregates for fine and coarse mixtures:Grading No. 1: No. 4 to No. 100 sieve (4.75 mm to 150 μm),and No. 2: 3/8 in. to No. 100 sieve (9.5 mm to 150 μm).

f600100



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GUIDE TO FIBER-REINFORCED SHOTCRETE 506.1R-3

3.2—FibersFibers for use in shotcrete can be made of steel, glass,

synthetic polymers, and natural materials. Only steel andsynthetic fibers are considered herein because they are themost commonly used. Figures 3.1 and 3.2 illustrate steel andmacrosynthetic fibers being used in shotcrete.

Fibers for use in shotcrete are generally divided into twogroups by their diameter. Fibers with equivalent diametersgreater than 0.012 in. (0.3 mm) are known as macrofibers;fibers with diameters less than 0.012 in. (0.3 mm) are knownas microfibers. The descriptor denier is often used to indicatethe fineness of microfibers. A typical synthetic shotcretemicrofiber has a denier of 6, which results in an equivalentdiameter of 0.0012 in. (32 μm). More information on fibers,denier, and equivalent diameters can be found in ACI 544.1R.

One parameter to characterize macrofibers is the aspectratio. Typical aspect ratios of macrofibers for shotcrete rangefrom 40 to 65 for common fiber lengths of 0.75 to 2 in. (19to 50 mm), although steel fiber lengths are generally lessthan 1.5 in. (38 mm). Synthetic microfiber lengths vary from0.25 to 2 in. (6 to 50 mm).

ASTM C1116/C1116M defines the required properties ofFRS and fibers used in shotcrete.

3.2.1 Macrofibers—Macrofibers are defined as thosefibers for use in shotcrete with equivalent diameters greaterthan 0.012 in. (0.3 mm). The majority of macrofibers used inshotcrete are either steel or synthetic fibers. Steel fibers usedin shotcrete are generally between 0.75 to 1.4 in. (19 to 35 mm)in length and 0.016 to 0.03 in. (0.4 to 0.8 mm) in equivalentdiameter. Synthetic macrofibers can be longer and varybetween 1.5 to 2 in. (40 to 50 mm) long, with equivalentdiameters similar to the steel fibers. The fibers should meetthe requirements of ASTM C1436.

3.2.2 Microfibers—Microfibers used in shotcrete arenormally polyolefin-based or nylon, and should meet therequirements of ASTM C1436. If the microfibers are used toresist explosive spalling in fires, then fibers should bepolypropylene, with equivalent diameters less than 0.0013 in.(33 μm) and less than 0.5 in. (12 mm) long (Tatnall 2002).

3.3—Other materials While the normal materials used in shotcrete are used in

FRS, supplementary cementitious materials are often used,such as silica fume, slag, and fly ash. For applications thatrequire vertical and overhead placement with macrofibers,these materials can help build thicker layers withoutsloughing and reduce fiber rebound. For shotcretes thatcontain more than about 0.3% by volume of fibers, the additionof water-reducing admixtures is common to maintain desiredwater-cementitious material ratios. Admixtures that meet therequirements of ASTM C1436 are normally acceptable foruse in FRS.

CHAPTER 4—MIXTURE PROPORTIONS4.1—General

Proportioning shotcrete mixtures that contain fibersshould follow the general guidelines outlined in ACI 506R.While FRS mixtures are normally proportioned to attain aspecified compressive strength, many times an ultimate flexuralstrength and postcrack performance, such as residualstrength(s), or an energy absorption, toughness, or both, arespecified. Nonfibrous shotcrete proportioning methodsshould be used to attain compressive and flexural require-ments (ACI 506R), and the recommendations from fibersuppliers selected for the type (material and shape) andquantity of fibers to attain postcrack performance require-ments should be used.

4.2—Wet processFRS for wet-process shotcrete is typically delivered to the

pump in accordance with ASTM C1116/C1116M. Becauserebound of macrofibers is typically less in wet-process shotcrete,fiber dosages are sometimes less than for dry-process shotcretefor the same postcrack performance. Steel fiber quantities usedare in the range of 20 to 100 lb/yd3 (12 to 60 kg/m3).Macrosynthetic fiber quantities are usually in the range of8.5 to 15 lb/yd3 (5 to 9 kg/m3). Microsynthetic fibers arenormally used at dosages of 1 to 4 lb/yd3 (0.6 to 2.4 kg/m3).

4.3—Dry processDry-process shotcrete can be delivered to the shotcrete

machine in transit mix trucks, volumetric batcher, in

Fig. 3.1—Examples of steel fibers.

Fig. 3.2—Examples of macrosynthetic fibers.



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prepared prepackaged containers, or mixed on site. Becauserebound of fibers in dry-process is normally greater thanrebound of fibers for wet-process shotcrete, fiber quantitiesmay be slightly higher than those indicated in Section 4.2(Dufour et al. 2006). Therefore some macrosynthetic fibersdo not lend themselves to successful shooting using the dry-process because they do not get coated with the cementitiouspaste and can tend to fly away in the shotcrete stream. Usersshould check with the fiber suppliers before using syntheticfibers when using the dry process.

CHAPTER 5—PRODUCTION5.1—General

Production of shotcrete follows closely the productionprocedures for producing concrete. Tolerances for batchingmaterials should follow established provisions for concrete.

5.2—Batching and mixing 5.2.1 Wet process—Wet-process FRS should be batched

and mixed in accordance with ASTM C1116/C1116M,which covers plant batching and mixing, transit truckmixing, and volumetric plant batching and mixing. Fibersmay be added to a plant mixer by depositing them on top ofaggregates just before they are introduced into the mixer.Various fiber dispensers have been developed to measureand add fibers to the mixture. When fibers are added to atransit mixer, they should be added at a rate of about 100 lb/minute (45 kg/minute) for steel fibers, and about 10 lb/minute (4.5 kg/minute) for synthetic fibers while the mixeris turning at maximum speed. When using a volumetricbatcher, a dispenser is essential to obtaining the proper quantityof fibers in the mixture. If fibers are added to a transit mixeron site, adequate mixing time should be attained to ensuredispersion of the fibers. A minimum of 40 revolutions of themixer after fiber addition should be recorded. Furtherguidance for production of FRS is available in ACI 544.3R.

5.2.2 Dry process—Dry-process shotcrete may be batchedand mixed as for wet-process shotcrete except water is notadded to the mixture. Adequate mixing should be ensured toachieve good fiber distribution. In many cases, packaged,dry, combined FRS mixtures are delivered to the project site.They are used for both dry-process FRS, and are sometimesplaced in a mixer with water added to produce wet-processFRS. If used for FRS, these materials should meet the require-ments of ASTM C1480/C1480M for Grade FR shotcrete.

5.3—Application 5.3.1 Equipment for FRS—Generally all the equipment

used for nonfibrous shotcrete application are used in the appli-cation of FRS. Grates used over pump hoppers should be usedwith FRS, and some manufacturers offer grates designed toaccommodate pumping FRS. As with nonfibrous shotcrete,dry-process FRS should be predampened. Predampeninghelps to reduce fiber rebound and fibers that fly away.

5.3.2 Application—All proper techniques of applying shot-crete, including safety requirements, as outlined in ACI 506Rshould be used to apply FRS. While fibers tend to orientatethemselves in the plane of the shotcrete structure, some fibers

may protrude the surface. If this is objectionable, a thin coaton nonfibrous shotcrete may be applied to cover the fibers.

CHAPTER 6—TEST PROCEDURES6.1—General

Many test methods used for nonfibrous concrete and shot-crete may be applicable to FRS, such as ASTM C143/C143M, C138/C138M, C42/C42M, and C78. ASTM testmethods directly applicable to FRS are mentioned in ACI544.2R, and updated annually in Shotcrete magazine(Tatnall 2007). ASTM C1609/C1609M (a beam test) andASTM C1550 (a flexural panel test) are important becausethey evaluate the postcracking flexural performance of fiber-reinforced concrete and FRS. A more detailed discussion ofFRS testing follows.

6.2—Fresh properties6.2.1 Consistency and pumpability—ASTM C143/C143M is

typically used to measure the consistency of wet-processshotcrete from batch to batch. This method uses samples ofFRS taken as the shotcrete is delivered to the pump. Astandardized test method has not yet been developed tocharacterize the pumpability of a mixture.

6.2.2 Unit density and air content—ASTM C138/C138Mmay be used to determine the unit density and air content ofFRS. ASTM C231 and C173/C173M may also be used todetermine air content. For wet-process FRS, the samples arenormally taken as the shotcrete is delivered to the pump. Fordry-process FRS, samples should be taken from the shotsection or panels shot for sampling purposes and tests can beconducted using the same test methods. For wet-processFRS, samples may also be taken from shot panels.

6.3—Hardened properties6.3.1 Strength—Specimens of shotcrete, including FRS,

for assessing the hardened properties should always be takenfrom sections that have been shot in-place or from panelsshot for the purpose. Specimens made from concrete beforeit is shot will not reflect the compactive effort, mixingactions, and rebound effects on the final shotcrete structure.Panels shot for sampling should be prepared in accordancewith ASTM C1140.

6.3.1.1 Compressive strength—Shotcrete specimensshould be obtained and tested in accordance with ASTMC1604/C1604M.

6.3.1.2 Flexural strength—Shotcrete specimens shouldbe obtained in accordance with ASTM C42/C42M. Flexuralstrength may be obtained using either ASTM C78 or C293,although C78 is the more common test method used. Typically,4 x 4 x 14 in. (100 x 100 x 350 mm) specimens are used forflexural testing. See also Section 6.3.2.2.

6.3.1.3 Shear strength—The Japan Concrete Institutepublished a test method (JCI-SF 6) for determining the punchingshear strength of fiber-reinforced concrete that may be used toassess FRS. Beam specimens are loaded in a jig to producethe punching action, and shear strength is reported as the loaddivided by two times the width and depth of the specimen.



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6.3.1.4 Bond strength—Although there is no ASTM testmethod for shotcrete bond to substrate, ASTM C1583/C1583M can be used to determine the direct tensile pulloffbond strength. “European Specification for Sprayed Shot-crete” (EFNARC 1996) recommends a similar test methodfor bond strength determination.

6.3.2 Toughness—Toughness with respect to FRS generallyrelates to the ability of a shotcrete specimen to absorb energybefore and after cracking, and is normally considered in theflexural mode of failure, although compressive toughnesshas been measured (JCI-SF 5). Described another way, it isa measure of the specimen’s ability to carry load aftercracking. A number of test methods have been developed tocharacterize toughness of FRS.

6.3.2.1 Energy absorption—ASTM C1609/C1609Mand C1550 are used to determine the energy absorption ofFRS specimens. ASTM C1609/C1609M uses a square crosssection flexural beam specimen with a span-depth ratio of 3,and FRS is normally tested using a specimen with a depth of4 in. (100 mm). The load versus central deflection isrecorded for third-point loading, and a load-deflection curveis plotted. The area under the load-deflection curve fromstart to an end-point deflection of span/150 is reported as theenergy absorbed, . In ASTM C1550, a 31.5 in. (800mm) diameter round panel, 3 in. (75 mm) thick, is supportedon three symmetrically arranged pivots and subjected to acentral point load. The load and deflection are recorded toproduce a load-deflection curve. The area under this curve isintegrated to produce an energy-versus-deflection curve.Energy quantities may be determined at selected deflectionsup to 1.6 in. (40 mm). Figure 6.1 illustrates an ASTM C1550load-deflection and the resulting energy-deflection curve.

6.3.2.2 Postcrack strength—ASTM C1609/C1609Mcan be used to determine the postcrack flexural strength ofFRS. In this test method, the postcracking strengths aretermed residual strengths, and are reported at deflections ofspan/600 and span/150; the user may select other deflectionsgreater than span/600. The residual strengths required to bereported for a typical 4 in. (100 mm) deep specimen are

TXXXD

termed and , where the superscript indicates thespecimen depth in millimeters, and the subscript indicatesdeflection in terms of span/xxx. In this test method, the first-peak and ultimate strengths (modulus of rupture) are alsoreported. Figure 6.2 shows an example of a load-deflectiondiagram that was recorded using ASTM C1609/C1609Mand the various parameters reported. ASTM C1399 may beused to determine the average residual strength of a FRSbeam specimen. The beam is cracked in a controlled manner,then the load-versus-deflection curve is generated. Residualloads are determined and averaged at specified deflections,and the strength after cracking is reported.

6.3.3 Other methods6.3.3.1 Density, boiled absorption, and permeable voids—

ASTM C642 is typically used to determine the density,

f600100 f150

100

Fig. 6.1—Example of ASTM C1550 load-deflection curve and integration of area under curve.

Fig. 6.2—Example of ASTM C1609/C1609M load-deflectiondiagram and flexural parameters.



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absorption, and permeable voids of FRS. Determining thesecharacteristics provides an indication of the quality of thematerials and application of FRS.

6.3.3.2 Explosive spalling—EFNARC and others inEurope are developing a standard test method to assessthe probability of explosive spalling of concrete and shot-crete when subjected to a high-temperature-rise fire, suchas those fuelled by hydrocarbons. Many investigators usethe Rijkswaterstaat (RWS) temperature-versus-time curve,which increases the furnace temperature from ambient to2462 °F (1350 °C) in about 15 minutes, and then holds thetemperature for 2 hours. The loss in FRS mass is thenmeasured (TNO 1996).

CHAPTER 7—PERFORMANCEOF FIBER-REINFORCED SHOTCRETE

7.1—Flexural strength Macrofibers are added to increase the postcracking flexural

strength (the ability to carry flexural loads after cracking).In general, fibers are not added to shotcrete to increase theflexural strength of shotcrete. This postcrack performance ismeasured as energy absorbed after cracking. Two ASTMtest methods were developed to measure the toughness ofFRS. ASTM C1609/C1609M is a flexural beam test methodthat normally uses 4 x 4 x 14 in. (100 x 100 x 350 mm) speci-mens sawn from shot panels and tested on a 12 in. (300 mm)span in third-point loading. Net central beam deflections andloads are recorded and used to produce a load-deflectiondiagram. Postcracking loads are determined at specifieddeflections of span/600 and span/150, and converted toresidual engineering strengths using elastic analysis. Thetotal area under the load-deflection diagram is calculatedusing an end-point deflection of span/150, and reported astoughness (Fig. 6.2).

ASTM C1550 is also a flexural test method developedusing a round panel specimen 31.5 in. (800 mm) in diameter,3 in. (75 mm) thick. The panel is supported symmetrically atthree evenly spaced points at the perimeter and centrallyloaded. Appropriate end-point deflections are selected basedon the intended application. The net central deflections andloads are recorded and used to produce a load-deflectiondiagram. The area under the load-deflection diagram isintegrated to produce an energy-versus-deflection curve thatis used to evaluate the performance of FRS (Fig. 6.1).

The beam test method has the advantage of resulting inmaterial flexural strengths that can be used in engineeringdesign and serviceability considerations as illustrated inChapter 8. The difficulty in determining net deflections andusing the required closed-loop, servo-controlled testingmachines, and the inherent variability of beam flexuraltesting are disadvantages. The round panel test method hasthe advantage of low variability, and the fact that the testspecimen is the shot-panel; thus, specimens do not have to besawn from it, which eliminates a step. The disadvantage isthat test results are reported in terms of energy (inch-poundsor Joules), which is not readily convenient for use bydesigners. Correlations between beam test results and paneltest results are not valid (Bernard 2004). The beam tests are

thus used in normal practice to determine the residualstrengths available from given fibers and dosages, while theround panel tests are used for quality control and assuranceduring construction.

7.2—Compressive strength The compressive strengths of FRS are not affected by the

inclusion of fibers when using typical fiber contents of from0.1 to 1% by volume. The mode of compressive failure maybe changed from brittle to a more yielding failure, dependingon the fiber used and the fiber content.

7.3—Shear strength The shear strength of FRS batched with macrofibers may

be increased depending on the fiber type and quantity offibers used, and the test method used to characterize shearstrength, as is true for fiber-reinforced concrete (ACI544.1R). Significant improvements in shear strength andshear toughness were reported by Mirsayah and Banthia(2002) for steel FRS, and improvements were also reportedfor macrosynthetic FRS (Majdzadeh et al. 2006).

7.4—Bond strength Bond strengths of FRS to rock have been reported from

30 to 540 psi (0.2 to 3.7 MPa) (Sandell 1977; Rose 1981;Talbot et al. 1994), depending on preparation of the substrateand the age at testing. Because there are no standardized testmethods to evaluate bond strength, many evaluations areconducted by drilling cylindrical cores through the shotcreteand substrate and pulling the two apart. The results of thisevaluation are variable, and the method requires a number ofcore samples for proper evaluation.

7.5—Rebound considerations 7.5.1 General—The factors that affect rebound encompass a

wide range of items and conditions. Generally, a greaterpercentage of steel fibers than aggregates rebound from thesubstrate. Ryan (1975) reported fiber retention of 40%overhead and 65% on vertical surfaces. Parker et al. (1975)reported fiber retention of 44 to 88% (average 62%) for dry-mix coarse aggregate mixtures shot onto vertical panels. Inthe Atlanta Research Chamber tests, the average rebound ina 10-minute test in which 2500 lb (1130 kg) of mixture wasshot was 22% for a 3 in. (75 mm) thick dry-mix placement.The fiber content before shooting was 3.3% by mass of thedry material, while fiber content in the rebound material was4.6% (Rose 1981). Tests have also indicated that steel fiberrebound is highly dependent on fiber geometry (Amelin andBanthia 1998a).

An example of less rebound was reported for a trial inNevada (Henager 1977) in which 4 yd3 (3 m3) of steel fibermixture consisting of 700 lb/yd3 (415 kg/m3) cement,2700 lb/yd3 (1602 kg/m3) sand, and 150 lb/yd3 (89 kg/m3)1/2 x 0.010 in. (13 x 0.25 mm) fiber placed 6 in. (150 mm)thick had a total estimated rebound of 10%. A control batchwithout fibers applied under identical conditions by the samepersonnel had an estimated rebound of 31%. The work wasdone in a tunnel, and included vertical and overhead surfaces.



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For dry-mix shotcrete, Parker et al. (1975) reportedaverage rebounds of 18.3 and 17.7% for a nonfibrousmixture and a fiber mixture, respectively, and concluded thatthe mere presence of fibers in a mixture does not affectrebound appreciably. Instead, other factors appear to bemore important than fiber.

Krantz (1984) stated, “Due to rebound, the effectiveamount of fibers is reduced to about only 50 to 70% of theamount in the mix in dry-mix shotcrete. For wet-mix shot-crete, the amount of fiber rebound is approximately 5 to 10%.”

7.5.2 Factors affecting rebound of fibers—Quantitativedata on rebound of SFRS with the dry-process were obtainedin a study that systematically investigated variables one at atime and used high-speed photography to observe the shot-crete airstream (Parker et al. 1975).

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 ofintended 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 fibers simplybouncing off the surface. When lower air pressure or less airwas used, the amount and velocity of the remnant air currentswas less, and the rebound of fiber was correspondingly less.Reducing air pressure or air volume, however, resulted inreduced in-place compaction.

Banthia et al. (1992, 1994) present data on the effect offive steel fiber geometries on rebound and other shotcretecharacteristics. They show ranges of fiber rebound for dry-process of 35 to 78%, and wet-process of 12 to 18%.

Very little is documented in the literature with respect torebound of macrosynthetic fibers. The use of monofilamentmacrosynthetic fibers in wet-mix shotcrete applications hasgrown significantly worldwide since their introduction in thelate 1990s. Unlike the stiffer steel fibers, which have to beused at relatively short lengths of approximately 1.2 in.(30 mm) to reduce line blockage, the more flexiblemacrosynthetic fibers can generally be used in well-propor-tioned wet-mix shotcrete mixtures at lengths ranging from 2 to3 in. (50 to 75 mm) without significantly reducing the pump-ability and shootability of the mixture. Due to excess fiberrebound and problems getting fibers through some dry-mixequipment, however, success in using macrosynthetic in dry-mix shotcrete is limited.

Dufour et al. (2006) identified key parameters that affectthe performance of monofilament macrosynthetic fiber indry-mix shotcrete. Modifications were made to the geometricalcharacteristics of a specific fiber type to eliminate the problemsobserved and enable the production of high-qualitymacrosynthetic dry-mix FRS. It was shown that the reboundof both steel and macrosynthetic fibers at dosages of 75 and11.6 lb/yd3 (45 and 6.9 kg/m3), respectively, was comparablewith a mixture that contained silica fume when shot at thewettest stable plastic consistency.

While the rebound of shotcrete for both mixturescontaining steel and macrosynthetic fibers was 19.8 and17.9%, respectively, of the total mass of shotcrete, it was

determined that the fiber rebound of the total mass of fibershot was 31.1 and 31.5%, respectively.

7.5.3 Conditions that reduce rebound—Parker et al.(1975) concluded that the rebound process differed duringestablishment of an initial critical thickness (Phase 1) andsubsequent shooting onto fresh shotcrete (Phase 2).

During Phase 1, anything that promotes adherence ofmaterial on the substrate should reduce rebound. This includesthe following mixture conditions: a high cement content;more fines in the mixture (fly ash or very fine sand); smallermaximum size aggregate; proper wetness of aggregates so thatparticles are well-coated with cement; and a finer gradation.

After initial critical thickness is established, Phase 2rebound is reduced by any condition or set of conditions thatmakes the shotcrete on the substrate softer or more plastic, atleast until it tends to drop off. Thus, for maximum reductionof Phase 2 rebound, shotcreting as wet as possible (that is,the wettest stable consistency) is one of the most beneficialand easiest conditions to control.

A large number of measures can be used to reduce reboundof steel FRS in the dry process. The most effective of thesemeasures (which also applies to nonfibrous shotcrete) seemsto be reduction of the air pressure, air velocity, or amount ofair at the nozzle; use of more fines and smaller aggregate; useof shorter, thicker fibers; predampening to get the correctmoisture content; and shotcreting at the wettest stableconsistency (Parker et al. 1975; Henager 1977).

7.6—Shrinkage crack controlThe use of fibers in concrete to control shrinkage cracking

has been demonstrated for many years (ACI 544.1R).Microfibers used in concrete and shotcrete can provide resis-tance to plastic shrinkage cracking due to excessive moistureloss at early ages at volume percentages as low as 0.1%(Padron and Zollo 1990). Macrofibers, on the other hand,provide resistance to drying shrinkage cracking and controlcrack widths at dosages as low as 0.25% by volume (Grzy-bowski and Shah 1990). When shotcrete is used in thinlayers, and curing conditions may not be favorable, the useof fibers can mitigate potential cracking distress.

One of the major problems with dry-process shotcrete isthe high aggregate rebound. Further, large aggregate particleshave a tendency to rebound as much as four times the rate ofsmall particles (Amelin et al. 1997). This increases thecementitious content in the in-place shotcrete sometimes byas much as a factor of 2 (Amelin and Banthia 1998b). Withvery high cementitious contents and inadequate curing,early-age shrinkage cracking in dry-process shotcrete is amajor concern. This is particularly true for high surface-volume ratio placements such as repairs and lining elementswhere shotcrete is generally fully restrained, and largeamounts of water may evaporate early on.

Fiber reinforcement is one of the most effective ways ofcontrolling plastic and drying shrinkage-induced cracking indry-process shotcrete. Research results (Banthia and Campbell1998) indicate that both steel and synthetic macrofibers areeffective. Fibers not only delay the formation of cracks, butalso reduce crack widths and total crack areas. The geometry



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of the fiber has a strong influence on its crack arrest capabil-ities. Excessive loss of fiber, however, may also occurthrough rebound in dry-process shotcrete, thereby dimin-ishing the effectiveness of fiber reinforcement.

7.7—Impact resistance Shotcrete linings in rock stabilization and underground

support construction in mines and tunnels are highlysusceptible to impact loads caused by blasting or rock bursts.In deeper hard-rock mines, the high in-place and mining-induced stresses in the rock lead to rock bursts in the form ofextensive, unstable rock fractures and rock-mass dilationthat causes sudden ground movement in openings and drifts.Rock burst hazards increase as mines advance to greaterdepths, and high-quality ground support is required to minimizerock burst damage and to enhance the safety of the workers.Rock burst conditions impart large amounts of impact load,and if the shotcrete does not possess adequate impactresistance, failure may occur. Although nonmining shotcreteapplications are possibly less vulnerable to impact loads,these may not be summarily ruled out.

Fiber reinforcement of shotcrete is one of the most effectiveways of increasing the impact resistance of shotcrete. In alarge study at the University of British Columbia (Gupta etal. 2000; Banthia et al. 1999a,b,c,d), 10 different types offibers were investigated for their effectiveness at enhancingthe impact resistance of wet-process shotcrete. Instrumented

impact tests were performed and comparisons were madewith companion quasi-static tests. Both beams and platespecimens were tested. Results indicated that fiber reinforce-ment was highly effective in improving the fracture toughnessunder impact loading. Steel fibers were found to be the mosteffective, but the improvements depended on the geometryof the fiber. In the case of synthetic fibers, while polypropyleneor polyvinyl alcohol macrofibers adequately improved theresistance of shotcrete to impact loads, pitch-based carbonmicrofibers were seen as relatively ineffective. Resultsfurther demonstrated that FRS is a highly strain-rate-sensitivematerial, and its fracture toughness under high rates ofloading (such as those occurring under impact) is verydifferent from its fracture toughness under quasi-static rates ofloading. In some instances, FRS was seen to absorb less energyunder impact loading than under quasi-static rates of loading.

7.8—Thermal explosive spallingMicrofibers of polypropylene in shotcrete have demonstrated

resistance to explosive spalling when subjected to high-temperature-rise fires, such as those fueled by hydrocarbons(Tatnall 2002). The fibers should have an equivalent diameterof less than 0.0013 in. (33 μm), and used in shotcrete tunnellinings at dosages of 1.6 to 3.4 lb/yd3 (1 to 2 kg/m3) forexplosive spalling resistance (Tatnall 2002). Figure 7.1shows shotcrete panels with and without microfiberssubjected to fire testing.

CHAPTER 8—DESIGN CONSIDERATIONS8.1—General

FRS has been used successfully for ground support formore than 25 years. Performance attributes are typicallyconsidered to be holding, retaining, and reinforcing.Although design with FRS and conventional shotcrete isbasically the same, the material properties can be signifi-cantly different, thereby allowing considerable difference inshotcrete thickness and amount of reinforcement. Mostavailable design data are for ground support, such as in tunnellinings. Simplistic and typically conservative analyticalmodels have been developed from observation of shotcreteperformance under service conditions and from large-scaletesting in laboratory and field facilities (Vandewalle 2005).

8.2—Empirical design The earliest empirical guidelines were developed from

local experience for underground rock support, and the use ofthem in other locales may not lead to adequate results becauseof changing geological and construction conditions. For morethan 30 years, engineers have used rock mass classificationsystems such as rock mass rating (RMR) system and rockmass quality (Q) system to correlate shotcrete experience indiffering ground conditions (Grimstad et al. 2002) Theseguidelines can be used to estimate shotcrete thickness, bidquantities, and support requirements during construction.

Grant et al. (2001) presented a method to relate theempirically produced Barton chart (Grimstad and Barton1993) to toughness values for SFRS based on a European testmethod. Papworth (2002) expanded the 2001 work to

Fig. 7.1—Explosive spalling loss due to rapid temperature-rise heating from hydrocarbon fire.



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include recommendations for FRS toughness values requiredbased on ASTM C1550 tests using 1.6 in. (40 mm) centraldeflections for various values of rock quality, and deformationsexpected for both steel and macrosynthetic FRS.

8.3—Comparable moment capacity One method to estimate the required fiber quantity is to

compare the moment capacity of a conventionally reinforcedshotcrete section to the moment capacity of an FRS section(Vandewalle 2005). In the conventionally reinforced section,the shotcrete is assumed cracked, and the welded wirereinforcement or reinforcing bars carry the entire tensile(flexural) load. The moment capacity may be calculated from

Mo. CapConv. = φAS fY (d – a/2) (8-1)

The moment capacity of an FRS section, which is assumedcracked, can be calculated from its residual strength asdetermined from the ASTM C1609/C1609M test results,and the section modulus of the FRS section, as follows

Mo. CapFRS = bt2/6 (8-2)

Setting the conventionally reinforced moment capacityequal to the FRS moment capacity, one can calculate theresidual strength required, and, based on testing, determinethe quantity of selected fibers required to provide theresidual strength and, thus, the moment capacity required forcomparable capacity of the FRS section (Vandewalle 1993).An example is illustrated in the Appendix.

CHAPTER 9—SPECIFICATION AND QUALITY CONTROL CONSIDERATIONS

9.1—GeneralSpecifications for FRS should generally follow the recom-

mendations found in ACI 506R and ACI 506.2 for shotcrete.Additional requirements should be added to specify the typeor types (material) of fibers allowed, and either the perfor-mance criteria required or the type and quantity of fibersrequired. The user is cautioned that specification of aminimum dosage rate is not a guarantee of a minimumperformance level. Specification of a performance levelincludes the synergistic effects of concrete flexural strengthand fiber material, type, and dosage rate. Materials for FRSshould meet the requirements of ASTM C1436. Materialsfor prepackaged, preblended, dry, combined shotcreteshould meet the requirements of ASTM C1480/C1480M forGrade FR shotcrete.

9.2—Performance specificationsIf fibers are added to control plastic shrinkage cracking or

to provide resistance to explosive spalling in fires, it is bestto prescribe the type, size, and quantities of fibers requiredper cubic yard (cubic meter) of shotcrete. Macrofibers arenormally used to increase the toughness and residualstrength of the shotcrete in flexure, not the compressivestrength nor the ultimate flexural strength (modulus ofrupture). The specifier should establish criteria, in addition

to the required compressive and flexural strengths, for theresidual strength(s) required. Typically in specifications forground support, 7-day flexural and residual strengths arerequired. For conditions where small deformations of theshotcrete are expected and minimum limits on crack widthare required, the specifier should consider a residual strengthat small deflection, such as , which is the residual strengthat a test beam deflection of the span/600, or at 0.02 in. (0.5 mm).If, on the other hand, large deformations are expected andcrack widths are not as critical in the structure, then a residualstrength should be specified at a larger beam deflection, such as

, which is the residual strength at a deflection of span/150, or 0.078 in. (2.0 mm). Typical residual strength valuesspecified for ground support FRS are ≥ 50% of themodulus of rupture, and ≥ 30% of the modulus of rupture.

The 1.6 in. (40 mm) end-point deflection value in ASTMC1550 was chosen to evaluate crack widths primarilyassociated with mining applications. A smaller deflection,such as 0.27 to 0.39 in. (7 to 10 mm), should be used whenspecifying C1550 test results for civil tunnels (Bernard 2004).

9.3—Prescriptive specifications Prescriptive specification of FRS is not recommended,

except as described previously for microfibers, unless thedesigner and specifier have knowledge of the performance ofthe specific fiber and dosage specified. If this type specificationis used, guidance should be provided for utilization ofalternative fibers and dosages.

CHAPTER 10—APPLICATIONS10.1—General

Applications of FRS include slope stabilization projects,mining and tunneling ground support, dam repairs andupgrades, bridge superstructure repairs, and sealing unstableground. Examples of some applications follow.

10.2—Ground support10.2.1 Tunneling—A recent example of both macrofiber

and microfiber reinforced shotcrete is the renovationcompleted in 2005 of the 1880s Weehawken Tunnel in NewJersey for use on the Hudson-Bergen Light Rail rapid transitsystem. The old brick-lined railroad tunnel through the Pali-sades was enlarged to handle the transit line and install astation halfway through the 4154 ft (1266 m) long tunnel.The 42 ft (12.8 m) diameter shaft for the station elevators andthe running tunnel used steel fiber-reinforced shotcrete forinitial support. The transition section between the 27 ft (8.2 m)wide tunnel and the 65 ft (19.8 m) wide station used steelFRS with micropolypropylene fibers for explosive spallingprotection in case of fires in the final lining (Garrett 2004;Tatnall 2007). Figures 10.1 and 10.2 show FRS applied in theWeehawken tunnel and the nearby Exchange Place tunnels.

10.2.2 Mining—Rispin et al. (2005) reported on the use ofsteel fibers in shotcrete in deep hard-rock mining in Ontario,Canada, where the use of SFRS and rock bolts serve as theground support system and facilitate the use of roboticapplication of the shotcrete that keeps miners from workingunder unsupported rock (Fig. 10.3). Owners of the Perseverance

f600100

f600100

f150100

f600100

f150100



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Mine in Western Australia used macrosynthetic fibers in shot-crete with and without rock bolts for ground control in verypoor rock with high deformation; the macrosynthetic FRSdemonstrated strain-hardening capabilities after cracking(Clements and Bernard 2004). O’Donnell (2000) describedthe usage development of SFRS as the primary support systemfor a mine in Ontario, Canada at depths to 7000 ft (2130 m).He concluded that the benefits were safer workplaces,productivity gains, reduction in reconditioning costs, quickerand safer remediation work, increased stability of drill holecollars, and verification that 84 lb/yd3 (50 kg/m3) of a 1.25 in.(30 mm) deformed steel fiber was an adequate fiber contentfor the deformations experienced in this mine.

10.2.3 Slope stabilization10.2.3.1 Rock and earth slopes—Keienburg (2006)

described the use of SFRS for stabilizing an open pit mine inSouth Africa. Ballou (2004) described rock-slope stabiliza-tion projects in the western U.S., and outlined some of the

advantages for using FRS, including costs, aesthetics, andschedule. Journeaux (2004) detailed the rock-slope stabiliza-tion of the historic King’s Bluff and the Weehawken TunnelPortal in New Jersey using prepackaged, tinted dry-processSFRS.

10.2.3.2 Soil nailing—Ballou and Niermann (2002) andSmith et al. (1993) described techniques for using SFRS forsoil nailing projects in the U.S.

10.3—Rehabilitation and repairExamples of repairs to structures include the ongoing

repairs to berth facing at the Port of Saint John, NB (Gilbrideet al. 2002), where SFRS was used to rebuild deterioratedconcrete berths at a port that experiences 33 ft (10 m) seatides that cause many cycles of wetting and drying andfreezing and thawing (Fig. 10.4). Experience at this portsince 1982 with using steel fiber-reinforced concrete andshotcrete shows that the steel fibers do not corrode, even inthis severe environment, except for the first few tenths of aninch (millimeters) after many years of service. Repairs toberths, wharves, and dolphins using microsynthetic fibers inthe Caribbean are described by Hutter et al. (2007), and therepairs to the Pointe de la Prairie Lighthouse in Québec wonthe American Shotcrete Association Outstanding Repair andRehabilitation Award (Giroux and Reny 2006).

In 1994, a 4 in. (100 mm) thick bonded overlay of SFRSwas used to stiffen the arches of the Littlerock Dam inSouthern California in a seismic retrofit project. Forrest et al.(2004) outline many details of this project, including thedesign basis, preparation, quality control and assuranceprocedures, mixture proportions, and application procedures.

10.4—Architectural shotcreteGarshol (2000) described the use of steel FRS to build a 36 ft

(11 m) tall troll at an amusement park in Norway. In 1999, aseries of concrete lions on the Centre Street Bridge inCalgary, AB were rehabilitated using prepackagedmicrofiber-reinforced shotcrete (Kroman et al. 2002).

Fig. 10.1—Weehawken tunnel and station shaft: initial steelfiber-reinforced shotcrete lining.

Fig. 10.2—Exchange Place final lining steel fiber-reinforcedshotcrete.

Fig. 10.3—Shooting with robotic arm holding nozzle.



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10.5—Explosive spalling resistance Due to a number of extreme fires in highway and rail

tunnels and the resulting damage to concrete and shotcretelinings, many new tunnels are using low dosages (1.6 to 5 lb/yd3

[1 to 3 kg/m3]) of micropolypropylene fibers to resist explosivespalling of shotcrete. Examples include the WeehawkenTunnel in New Jersey (Garrett 2004), the 35 mile (57 km)long Gotthard Base twin rail tunnels through the Swiss Alps(Spirig 2004). Polypropylene fibers were specified for theBindermichl tunnel Linz and the U2/U5 tunnel in Vienna,Austria (Winterberg and Dietze 2004).

CHAPTER 11—REFERENCES11.1—Referenced standards and reports

The standards and reports listed below were the latesteditions at the time this document was prepared. Becausethese documents are revised frequently, the reader is advisedto contact the proper sponsoring group if it is desired to referto the latest version.

American Concrete Institute506R Guide to Shotcrete506.2 Specifications for Shotcrete544.1R Report on Fiber Reinforced Concrete544.2R Measurement of Properties of Fiber Reinforced

Concrete544.3R Guide for Specifying, Proportioning, and Produc-

tion of Fiber-Reinforced Concrete

ASTM InternationalC42/C42M Test Method for Obtaining and Testing

Drilled Cores and Sawed Beams of ConcreteC78 Test Method for Flexural Strength of

Concrete (Using Simple Beam with Third-Point Loading)

C138/C138M Test Method for Density (Unit Weight),Yield, and Air Content (Gravimetric) ofConcrete

C143/C143M Test Method for Slump of Hydraulic-Cement Concrete

C173/C173M Test Method for Air Content of FreshlyMixed Concrete by the Volumetric Method

C231 Test Method for Air Content of FreshlyMixed Concrete by the Pressure Method

C293 Test Method for Flexural Strength ofConcrete (Using Simple Beam with Center-Point Loading)

C642 Test Method for Density, Absorption, andVoids in Hardened Concrete

C1116/C1116M Specification for Fiber-Reinforced ConcreteC1140 Practice for Preparing and Testing Speci-

mens from Shotcrete Test PanelsC1399 Test Method for Obtaining Average

Residual-Strength of Fiber-ReinforcedConcrete

C1436 Specification for Materials for ShotcreteC1480/C1480M Specification for Packaged, Pre-Blended,

Dry, Combined Materials for Use in Wet orDry Shotcrete Application

C1550 Test Method for Flexural Toughness ofFiber Reinforced Concrete (Using CentrallyLoaded Round Panel)

C1583/C1583M Test Method for Tensile Strength ofConcrete Surfaces and the Bond Strength orTensile Strength of Concrete Repair andOverlay Materials by Direct Tension (Pull-off Method)

C1604/C1604M Test Method for Obtaining and TestingDrilled Cores of Shotcrete

C1609/C1609M Test Method for Flexural Performance ofFiber-Reinforced Concrete (Using Beamwith Third-Point Loading)

Japan Concrete Institute

JCI-SF 5 Method of Test for Compressive Strength andCompressive Toughness of Fiber ReinforcedConcrete

JCI-SF 6 Method of Test for Shear Strength of FiberReinforced Concrete

These publications may be obtained from these organizations:

American Concrete InstituteP.O. Box 9094Farmington Hills, MI 48333-9094www.concrete.org

ASTM International100 Barr Harbor Dr.West Conshohocken, PA 19428-2959www.astm.org

Japan Concrete InstituteMubanchi, Yotsuya 1-chrome, Shinjuku-kuTokyo 160, Japanwww.jsce.or.jp

Fig. 10.4—Shooting berth faces on rising tide at Port ofSaint John, NB, Canada.



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11.2—Cited referencesAmelin, H. S.; Banthia, N.; Morgan, D. R.; and Steeves, C.,

1997, “Rebound in Dry-Mix Shotcrete,” Concrete Inter-national, V. 19, No. 9, Sept., pp. 54-60.

Amelin, H. S., and Banthia, N., 1998a, “Steel FiberRebound in Shotcrete: Influence of Fiber Geometry,”Concrete International, V. 20, No. 9, Sept., pp. 74-79.

Amelin, H. S., and Banthia, N., 1998b, “Mechanics ofAggregate Rebound in Shotcrete (Part 1),” Materials andStructures, RILEM, V. 31, Mar., pp. 91-98.

Ballou, M., 2004, “Steep Slope Stabilization with Fiber-Reinforced Shotcrete,” Shotcrete, V. 6, No. 4, Fall, pp. 12-14.

Ballou, M., and Niermann, M., 2002, “Soil and Rock SlopeStabilization Using Fiber-Reinforced Shotcrete in NorthAmerica,” Shotcrete, V. 4, No. 3, pp. 20-23.

Banthia, N., and Campbell, K., 1998, “RestrainedShrinkage Cracking in Bonded Fiber Reinforced Shotcrete,”The Interfacial Transition Zone in Cementitious Composites,RILEM Proceedings, V. 35, E&FN Spon, pp. 216-223.

Banthia, N.; Gupta, P.; and Yan, C., 1999a, “ImpactResistance of Fiber Reinforced Wet-Mix Shotcrete, Part 1:Beam Tests,” Materials and Structures, RILEM, V. 32,Oct., pp. 563-570.

Banthia, N.; Gupta, P.; and Yan, C., 1999b, “ImpactResistance of Fiber Reinforced Wet-Mix Shotcrete, Part 2:Plate Tests,” Materials and Structures, RILEM, V. 32,Nov., pp. 643-650.

Banthia, N.; Gupta, P.; Yan, C.; and Morgan, R., 1999c,“How Tough is Fiber Reinforced Shotcrete? Part 1: BeamTests,” Concrete International, V. 21, No. 6, June, pp. 59-62.

Banthia, N.; Gupta, P.; Yan, C.; and Morgan, R., 1999d,“How Tough is Fiber Reinforced Shotcrete? Part 2: PlateTests,” Concrete International, V. 21, No. 8, Aug., pp. 62-66.

Banthia, N.; Trottier, J.-F.; Beaupré, D.; and Wood, D.,1994, “Influence of Fiber Geometry in Steel Fiber-ReinforcedWet-Mix Shotcrete,” Concrete International, V. 16, No. 6,June, pp. 27-32.

Banthia, N.; Trottier, J.-F.; Wood, D.; and Beaupré, D., 1992,“Steel Fiber Dry-Mix Shotcrete: Influence of Fiber Geometry,”Concrete International, V. 14, No. 5, May, pp. 24-28.

Bernard, E. S., 2004, “Design Performance Requirementsfor Fibre Reinforced Shotcrete Using ASTM C 1550,”Shotcrete: More Engineering Developments,” Taylor &Francis Group, Oct., pp. 67-80.

Clements, M. J. K., and Bernard, E. S., 2004, “The Use ofMacro-Synthetic Fiber-Reinforced Shotcrete in Australia,”Shotcrete, V. 6, No. 4, Fall, pp. 20-22.

Dufour, J.-F.; Trottier, J.-F.; and Forgeron, D., 2006,“Behavior and Performance of Monofilament Macro-Synthetic Fibres in Dry-Mix Shotcrete,” Proceedings, Shot-crete for Underground Support X, D. R. Morgan and H. W.Parker, eds., Whistler, BC, Canada, Sept., pp. 194-205.

EFNARC, 1996, “European Specification for SprayedConcrete,” European Federation of Producers and Applicatorsof Specialist Products for Structures, Aldershot, UK, 30 pp.

Forrest, M. P.; Morgan, D. R.; Obermeyer, J. R.; Parker,P. L.; and LaMoreaux, D. D., 2004, “Seismic Retrofit ofLittlerock Dam,” Shotcrete, V. 6, No. 1, Winter, pp. 20-26.

Garrett, R., 2004, “Construction Chemistry atWeehawken,” Tunnelling & Trenchless Construction, Dec.,pp. 21-25.

Garshol, K. F., 2000, “The Shotcrete Troll,” Shotcrete, V. 2,No. 1, Feb., p. 21.

Gilbride, P.; Morgan, D. R.; and Bremner, T. W., 2002,“Deterioration and Rehabilitation of Berth Faces in TidalZones at the Port of Saint John,” Shotcrete, V. 4, No. 4, Fall,pp. 32-38.

Giroux, P., and Reny, S., 2006, “2005 Outstanding RepairProject: Pointe de la Prairie Lighthouse,” Shotcrete, V. 8,No. 4, Fall, pp. 30-32.

Grant, N. B.; Ratcliffe, R.; and Papworth, F., 2001,“Design Guidelines for the use of SFRS in Ground Support,”Proceedings, International Conference on EngineeringDevelopments in Shotcrete, Hobart, Tasmania, Australia, E.S. Bernard, ed., Apr., pp. 111-118.

Grimstad, E., and Barton, N., 1993, “Updating of the Q-System for NMT,” Proceedings, International Symposium onSprayed Concrete, Fagernes, Norway, Oct. 17-21, pp. 46-66.

Grimstad, E.; Kankes, K.; Bhasin, R.; Magnussen, A. W.;and Kaynia, A., 2002, “Rock Mass Quality Q Used inDesigning Reinforced Ribs of Sprayed Concrete and EnergyAbsorption,” Proceedings, Fourth International Symposiumon Sprayed Concrete—Modern Use of Wet-Mix SprayedConcrete for Underground Support, Davos, Switzerland,Norwegian Concrete Association, Oslo, Sept., pp. 134-155.

Grzybowski, M., and Shah, S. P., 1990, “ShrinkageCracking in Fiber Reinforced Concrete,” ACI MaterialsJournal, V. 87, No. 2, Mar.-Apr., pp. 138-148.

Gupta, P.; Banthia, N.; and Yan, C., 2000, “Fiber ReinforcedWet-Mix Shotcrete under Impact,” Journal of Materials inCivil Engineering, V. 12, No. 1, Feb., pp. 81-90.

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

Henager, C. H., 1977, The Technology and Uses of SteelFibrous Shotcrete: A State-of-the-Art Report, Battelle-North-west, Richland, WA, Sept., 60 pp.

Hutter, J.; Dufour, J.-F.; and Fullam, N., 2007, “ShotcreteRepairs in Barbados—A Caribbean Experience,” Shotcrete,V. 9, No. 1, Winter, pp. 10-14.

Journeaux, D., 2004. “Rock Stabilization of Two HistoricallySensitive Rock Slopes Using Shotcrete,” Shotcrete, V. 6, No. 2,Spring, pp. 10-13.

Kaden, R. A., 1977, “Fiber Reinforced Shotcrete: Ririe Damand Little Goose (CPRR) Relocation,” Shotcrete for GroundSupport, SP-54, American Concrete Institute/American Societyof Civil Engineers, Farmington Hills, MI, pp. 66-88.

Keienburg, M., 2006, “Slope Stabilization in an Open PitMine,” Shotcrete, V. 8, No. 3, Summer, pp. 28-30.

Krantz, G. W., 1984, “Selected Pneumatic Gunites for Usein Underground Mining: A Comparative EngineeringAnalysis,” Bureau of Mines Information Circular 1984, U.S.Department of Interior, Washington, DC, 64 pp.

Kroman, J.; Morgan, D. R.; and Simpson, L., 2002,“Shotcrete Lions for Calgary’s Centre Street Bridge,”Shotcrete, V. 4, No. 1, Winter, pp. 4-8.



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Lankard, D. R.; Walker, A. J.; and Snyder, M. J., 1971,“R/M Batching and Placement of Steel Fibrous Concrete,”Concrete Products, V. 7, No. 10, Oct., pp. 60-61 and 72.

Majdzadeh, F.; Soleimani, S. M.; and Banthia, N., 2006,“Shear Strength of Reinforced Concrete Beams with a FiberMatrix,” Canadian Journal of Civil Engineering, V. 33,No. 6, June, pp. 726-734.

Mirsayah, A., and Banthia, N., 2002, “Shear Strength ofSteel Fiber Reinforced Concrete,” ACI Materials Journal,V. 99, No. 5, Sept.-Oct., pp. 473-479.

Morgan, D. R., and Heere, R., 2000, “Evolution of FiberReinforced Shotcrete,” Shotcrete, V. 2, No. 2, May, pp. 8-11.

O’Donnell, J. D. P., 2000, “Shotcrete: A Key to Advancesin Safety and Productivity in Mining,” Shotcrete, V. 2, No. 3,Aug., pp. 20-22.

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APPENDIX—EXAMPLE OF COMPARABLE MOMENT CAPACITY CALCULATION

Chapter 8 discusses design considerations, and Section 8.3provides a method and equations for comparing the momentcapacity of a conventionally reinforced shotcrete section tothat of an FRS section. An example of these calculations ispresented in this Appendix.

Example:Assume a shotcrete tunnel lining is 4 in. (102 mm) thick

using 5000 psi (34.5 MPa) shotcrete, and is reinforced withone layer of 4 x 4 x W4.0/W4.0 WWR (102 x 102-MW26 xMW26). The welded wire reinforcement is assumed in thecenter of the shotcrete lining. The yield strength of thewelded wire reinforcement, fY, is 65,000 lbf/in.2 (448.3 MPa).What is the post-cracking residual flexural strength requiredfor a comparable fiber-reinforced shotcrete section?

Inch-pound units SI unitsUsing Eq. (8-1):b = unit width = 12 in. (1 ft) b = 1 mAS = area of conventional

reinforcing per unit widthAS = 0.04 in.2 × 12 in./4 in. AS = 26 mm2 × 1000 mm/102 mm= 0.12 in.2/ft = 254.9 mm2/mfY = 65,000 lbf/in.2 fY = 448.3 N/mm2

fc′ = 5000 lbf/in.2 fc′ = 34.5 N/mm2

a = AS fY / 0.85fc′b

a = a =

a = 0.153 in. a = 3.897 mmt = section thickness = 4 in. t = 102 mmd = t /2 = 4 in./2 = 2 in. d = 102 mm/2 = 51 mm

Mo. CapConv = φASfY (d – a/2)Mo. CapConv = 0.9 × 0.12 × 65,000 = 0.9 × 254.9 × 448.3

× (2 – 0.153/2) × (51 – 3.897/2)Mo. CapConv = 13,503 in.-lb/ft = 5,044,677 N-mm = 5.045 kN-m

0.12 in.2 65,000 psi×

0.85 5000 psi 12 in.××--------------------------------------------------------- 254.9 mm2 448.3 N/mm2

×

0.85 34.5 N/mm2 1000 mm××---------------------------------------------------------------------------



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Using Eq. (8-2):Determine , residual strength required:

Mo. CapFRS = × b × t2/6

= 6 × Mo. Cap/b × t2, where Mo. Cap. is that of the conventional reinforcing.

= 6 × 13,503 in.-lb/ft/ = 6 × 5.045 kN-mm × 1000 mm/m/12 in./ft × 42 in.2 1 m × 1022 mm2

= 422 lbf/in.2 = 2.91 N/mm2

Thus, a 4 in. (102 mm) thick FRS lining with a postcrackresidual flexural strength of 422 psi (2.91 MPa) as determinedat 0.02 in. (0.5 mm) deflection ( ) using ASTM C1609/C1609M will provide comparable moment capacity to theconventionally reinforced lining.

f600100

f600100

f600100

f600100

f600100



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Guide to Fiber-Reinforced Shotcrete

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