506.1R_08.pdf

ACI 506.1R-08

Guide to Fiber-Reinforced Shotcrete

Reported by ACI Committee 506

First Printing November 2008 American Concrete Institute Advancing concrete knowledge

®


Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI. The technical committees responsible for ACI committee reports and standards strive to avoid ambiguities, omissions, and errors in these documents. In spite of these efforts, the users of ACI documents occasionally find information or requirements that may be subject to more than one interpretation or may be incomplete or incorrect. Users who have suggestions for the improvement of ACI documents are requested to contact ACI. Proper use of this document includes periodically checking for errata at www.concrete.org/committees/errata.asp for the most up-to-date revisions. ACI committee documents are intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. Individuals who use this publication in any way assume all risk and accept total responsibility for the application and use of this information. All information in this publication is provided “as is” without warranty of any kind, either express or implied, including but not limited to, the implied warranties of merchantability, fitness for a particular purpose or non-infringement. ACI and its members disclaim liability for damages of any kind, including any special, indirect, incidental, or consequential damages, including without limitation, lost revenues or lost profits, which may result from the use of this publication. It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. ACI does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards. Order information: ACI documents are available in print, by download, on CD-ROM, through electronic subscription, or reprint and may be obtained by contacting ACI. Most ACI standards and committee reports are gathered together in the annually revised Concrete Practice (MCP). American Concrete Institute 38800 Country Club Drive Farmington Hills, MI 48331 U.S.A. Phone: 248-848-3700 Fax: 248-848-3701

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ACI Manual of

ACI 506.1R-08

Guide to Fiber-Reinforced Shotcrete Reported by ACI Committee 506

Peter C. Tatnall† Chair Dudley R. Morgan * Secretary

Lawrence J. Totten Vice Chair

Jill E. Glassgold

Jeffery L. Novak *

Raymond C. Schallom, III *

Lars F. Balck, Jr.

Charles S. Hanskat

H. Celik Ozyildirim

Raymond J. Schutz

*

Warren L. Harrison

Harvey W. Parker

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*

Jon B. Ardahl

Michael Ballou

Jean-François Dufour* John R. Fichter

Mark R. Lukkarila

Michael Rispin

Philip T. Seabrook

Christopher M. Zynda

Gregory McKinnon

*

Subcommittee members who prepared this report. †Subcommittee Chair.

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

CONTENTS Chapter 1—Introduction and scope, p. 506.1R-2 1.1—Introduction 1.2—Scope 1.3—Historical background

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

Chapter 3—Materials, p. 506.1R-2 3.1—General 3.2—Fibers 3.3—Other materials

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

ACI Committee Reports, Guides, Manuals, Standard Practices, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.

Chapter 4—Mixture proportions, p. 506.1R-3 4.1—General 4.2—Wet-process 4.3—Dry-process

ACI 506.1R-08 supersedes ACI 506.1R-98 and was adopted and published November 2008. Copyright © 2008, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retri eval system or device, unless permission in writing is obtained from the copyright proprietors.

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506.1R-2

ACI COMMITTEE REPORT

Chapter 5—Production, p. 506.1R-4 5.1—General 5.2—Batching and mixing 5.3—Application

Chapter 6—Test procedures, p. 506.1R-4 6.1—General 6.2—Fresh properties 6.3—Hardened properties

Chapter 7—Performance of fiber-reinforced shotcrete, p. 506.1R-6 7.1—Flexural strength 7.2—Compressive strength 7.3—Shear strength 7.4—Bond strength 7.5—Rebound considerations 7.6—Shrinkage crack control 7.7—Impact resistance 7.8—Thermal explosive spalling

Chapter 8—Design considerations, p. 506.1R-8 8.1—General 8.2—Empirical design 8.3—Comparable moment capacity

Chapter 9—Specification and quality control considerations, p. 506.1R-9 9.1—General 9.2—Performance specifications 9.3—Prescriptive specifications

Chapter 10—Applications, p. 506.1R-9 10.1—General 10.2—Ground support 10.3—Rehabilitation and repair 10.4—Architectural shotcrete 10.5—Explosive spalling resistance

Chapter 11—References, p. 506.1R-11 11.1—Referenced standards and reports 11.2—Cited references

Appendix—Example of comparable moment capacity calculations, p. 506.1R-13 CHAPTER 1—INTRODUCTION AND SCOPE 1.1—Introduction Fiber-reinforced shotcrete (FRS) is mortar or concrete containing discontinuous discrete fibers that is pneumatically projected at high velocity onto a surface. Continuous meshes, woven fabrics, and long rods are not considered as discrete fiber-type reinforcing elements in this guide.

1.2—Scope This document provides information on fiber-reinforced shotcrete using synthetic and steel fibers. Topics covered include materials used, mixture proportions, production of shotcrete, 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, et al. (1971). Steel FRS (SFRS) was proposed for underground support by Parker in 1971 (Parker 1974). Additional trials were made by Poad in an investigation of new and improved methods of using shotcrete for underground support (Poad et al. 1975). Subsequently, the first practical applications of SFRS were made in a tunnel adit at Ririe Dam, ID in 1973 (Kaden 1977). Since that time, SFRS has been used throughout the world. Shotcrete using micropolypropylene fibers was first placed in Europe in 1968 (Hannant 1978). Macrosynthetic fibers for use in shotcrete were developed in the mid-1990s and have been used in mining and slope stabilization projects (Morgan and Heere 2000).

CHAPTER 2—NOTATION AND DEFINITIONS 2.1—Notation AS

= area of conventional steel per unit width

a

=

AS f Y /0.85 f c′ b

b

=

unit width of section

d

=

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 ASTM C1609/C1609M

f Y

=

yield strength of conventional reinforcement

f c′

=

compressive strength of shotcrete

t

=

FRS section thickness

φ

=

strength reduction factor, = 0.9 for flexure

100 600

2.2—Definitions aspect 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—MATERIALS 3.1—General FRS is conventional shotcrete with fibers added. Materials for use in FRS should conform to the requirements of ASTM C1436, which covers the typical materials used in shotcrete, including chemical and mineral admixtures, fibers, and the combined 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).

GUIDE TO FIBER-REINFORCED SHOTCRETE

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Fig. 3.2—Examples of macrosynthetic fibers. Fig. 3.1—Examples of steel fibers.

3.2—Fibers Fibers for use in shotcrete can be made of steel, glass, synthetic polymers, and natural materials. Only steel and synthetic fibers are considered herein because they are the most commonly used. Figures 3.1 and 3.2 illustrate steel and macrosynthetic fibers being used in shotcrete. Fibers for use in shotcrete are generally divided into two groups by their diameter. Fibers with equivalent diameters greater than 0.012 in. (0.3 mm) are known as macrofibers; fibers with diameters less than 0.012 in. (0.3 mm) are known as microfibers. The descriptor denier is often used to indicate the fineness of microfibers. A typical synthetic shotcrete microfiber has a denier of 6, which results in an equivalent diameter 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 aspect ratio. Typical aspect ratios of macrofibers for shotcrete range from 40 to 65 for common fiber lengths of 0.75 to 2 in. (19 to 50 mm), although steel fiber lengths are generally less than 1.5 in. (38 mm). Synthetic microfiber lengths vary from 0.25 to 2 in. (6 to 50 mm). ASTM C1116/C1116M defines the required properties of FRS and fibers used in shotcrete. 3.2.1 Macrofibers—Macrofibers are defined as those fibers for use in shotcrete with equivalent diameters greater than 0.012 in. (0.3 mm). The majority of macrofibers used in shotcrete are either steel or synthetic fibers. Steel fibers used in 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 equivalent diameter. Synthetic macrofibers can be longer and vary between 1.5 to 2 in. (40 to 50 mm) long, with equivalent diameters similar to the steel fibers. The fibers should meet the requirements of ASTM C1436. 3.2.2 Microfibers—Microfibers used in shotcrete are normally polyolefin-based or nylon, and should meet the requirements of ASTM C1436. If the microfibers are used to resist explosive spalling in fires, then fibers should be polypropylene, 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 that require vertical and overhead placement with macrofibers, these materials can help build thicker layers without sloughing and reduce fiber rebound. For shotcretes that contain more than about 0.3% by volume of fibers, the addition of water-reducing admixtures is common to maintain desired water-cementitious material ratios. Admixtures that meet the requirements of ASTM C1436 are normally acceptable for use in FRS.

CHAPTER 4—MIXTURE PROPORTIONS 4.1—General Proportioning shotcrete mixtures that contain fibers should follow the general guidelines outlined in ACI 506R. While FRS mixtures are normally proportioned to attain a specified compressive strength, many times an ultimate flexural strength and postcrack performance, such as residual strength(s), or an energy absorption, toughness, or both, are specified. Nonfibrous shotcrete proportioning methods should be used to attain compressive and flexural requirements (ACI 506R), and the recommendations from fiber suppliers selected for the type (material and shape) and quantity of fibers to attain postcrack performance requirements should be used.

4.2—Wet process FRS for wet-process shotcrete is typically delivered to the pump in accordance with ASTM C1116/C1116M. Because rebound of macrofibers is typically less in wet-process shotcrete, fiber dosages are sometimes less than for dry-process shotcrete for the same postcrack performance. Steel fiber quantities used are in the range of 20 to 100 lb/yd 3 (12 to 60 kg/m3). Macrosynthetic fiber quantities are usually in the range of 8.5 to 15 lb/yd 3 (5 to 9 kg/m 3). Microsynthetic fibers are normally used at dosages of 1 to 4 lb/yd 3 (0.6 to 2.4 kg/m3).

4.3—Dry process Dry-process shotcrete can be delivered to the shotcrete machine in transit mix trucks, volumetric batcher, in

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prepared prepackaged containers, or mixed on site. Because rebound of fibers in dry-process is normally greater than rebound of fibers for wet-process shotcrete, fi ber quantities may be slightly higher than those indicated i n Section 4.2 (Dufour et al. 2006). Therefore some macrosynthetic fibers do not lend themselves to successful shooting using the dryprocess because they do not get coated with the cementitious paste and can tend to fly away in the shotcrete stream. Users should check with the fiber suppliers before using synthetic fibers when using the dry process.

CHAPTER 5—PRODUCTION 5.1—General Production of shotcrete follows closely the production procedures for producing concrete. Tolerances for batching materials 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 truck mixing, and volumetric plant batching and mixing. Fibers may be added to a plant mixer by depositing them on top of aggregates just before they are introduced into the mixer. Various fiber dispensers have been developed to measure and add fibers to the mixture. When fibers are added to a transit 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 mixer is turning at maximum speed. When using a volumetric batcher, a dispenser is essential to obtaining the proper quantity of fibers in the mixture. If fibers are added to a transit mixer on site, adequate mixing time should be attained to ensure dispersion of the fibers. A minimum of 40 revolutions of the mixer after fiber addition should be recorded. Further guidance for production of FRS is available in ACI 544.3R. 5.2.2 Dry process—Dry-process shotcrete may be batched and mixed as for wet-process shotcrete except water is not added to the mixture. Adequate mixing should be ensured to achieve 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 sometimes placed in a mixer with water added to produce wet-process FRS. If used for FRS, these materials should meet the requirements 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 application of FRS. Grates used over pump hoppers should be used with FRS, and some manufacturers offer grates designed to accommodate pumping FRS. As with nonfibrous shotcrete, dry-process FRS should be predampened. Predampening helps to reduce fiber rebound and fibers that fly away. 5.3.2 Application—All proper techniques of applying shotcrete, including safety requirements, as outlined in ACI 506R should be used to apply FRS. While fibers tend to orientate themselves in the plane of the shotcrete structure, some fibers

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

CHAPTER 6—TEST PROCEDURES 6.1—General Many test methods used for nonfibrous concrete and shotcrete may be applicable to FRS, such as ASTM C143/ C143M, C138/C138M, C42/C42M, and C78. ASTM test methods directly applicable to FRS are mentioned in ACI 544.2R, and updated annually in Shotcrete magazine (Tatnall 2007). ASTM C1609/C1609M (a beam test) and ASTM C1550 (a flexural panel test) are important because they evaluate the postcracking flexural performance of fiberreinforced concrete and FRS. A more detailed discussion of FRS testing follows.

6.2—Fresh properties 6.2.1 Consistency and pumpability—ASTM C143/C143M is typically used to measure the consistency of wet-process shotcrete from batch to batch. This method uses samples of FRS taken as the shotcrete is delivered to the pump. A standardized test method has not yet been developed to characterize the pumpability of a mixture. 6.2.2 Unit density and air content —ASTM C138/C138M may be used to determine the unit density and air content of FRS. ASTM C231 and C173/C173M may also be used to determine air content. For wet-process FRS, the samples are normally taken as the shotcrete is delivered to the pump. For dry-process FRS, samples should be taken from the shot section or panels shot for sampling purposes and tests can be conducted using the same test methods. For wet-process FRS, samples may also be taken from shot panels.

6.3—Hardened properties 6.3.1 Strength—Specimens of shotcrete, including FRS, for assessing the hardened properties should always be taken from sections that have been shot in-place or from panels shot for the purpose. Specimens made from concrete before it is shot will not reflect the compactive effort, mixing actions, and rebound effects on the final shotcrete structure. Panels shot for sampling should be prepared in accordance with ASTM C1140. 6.3.1.1 Compressive strength—Shotcrete specimens should be obtained and tested in accordance with ASTM C1604/C1604M. 6.3.1.2 Flexural strength—Shotcrete specimens should be obtained in accordance with ASTM C42/C42M. Flexural strength 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 for flexural testing. See also Section 6.3.2.2. 6.3.1.3 Shear strength—The Japan Concrete Institute published a test method (JCI-SF 6) for determining the punching shear strength of fiber-reinforced concrete that may be used to assess FRS. Beam specimens are loaded in a jig to produce the punching action, and shear strength is reported as the load divided by two times the width and depth of the specimen.


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

6.3.1.4 Bond strength—Although there is no ASTM test method for shotcrete bond to substrate, ASTM C1583/ C1583M can be used to determine the direct tensile pulloff bond strength. “European Specification for Sprayed Shotcrete” (EFNARC 1996) recommends a similar test method for bond strength determination. 6.3.2 Toughness —Toughness with respect to FRS generally relates to the ability of a shotcrete specimen to absorb energy before and after cracking, and is normally considered in the flexural mode of failure, although compressive toughness has been measured (JCI-SF 5). Described another way, it is a measure of the specimen’s ability to carry load after cracking. A number of test methods have been developed to characterize toughness of FRS. 6.3.2.1 Energy absorption—ASTM C1609/C1609M and C1550 are used to determine the energy absorption of FRS specimens. ASTM C1609/C1609M uses a square cross section flexural beam specimen with a span-depth ratio of 3, and FRS is normally tested using a specimen with a depth of 4 in. (100 mm). The load versus central deflection is recorded for third-point loading, and a load-deflection curve is plotted. The area under the load-deflection curve from start to an end-point deflection of span/150 is reported as the D energy absorbed, T XX X . In ASTM C1550, a 31.5 in. (800 mm) diameter round panel, 3 in. (75 mm) thick, is supported on three symmetrically arranged pivots and subjected to a central point load. The load and deflection are recorded to produce a load-deflection curve. The area under this curve is integrated to produce an energy-versus-deflection curve. Energy quantities may be determined at selected deflections up to 1.6 in. (40 mm). Figure 6.1 illustrates an ASTM C1550 load-deflection and the resulting energy-deflection curve. 6.3.2.2 Postcrack strength—ASTM C1609/C1609M can be used to determine the postcrack flexural strength of FRS. In this test method, the postcracking strengths are termed residual strengths, and are reported at deflections of span/600 and span/150; the user may select other deflections greater than span/600. The residual strengths required to be reported for a typical 4 in. (100 mm) deep specimen are

Fig. 6.2—Example of ASTM C1609/C1609M load-deflection diagram and flexural parameters. 100

100

termed 600 and 150 , where the superscript indicates the specimen depth in millimeters, and the subscript indicates deflection in terms of span/xxx. In this test method, the firstpeak and ultimate strengths (modulus of rupture) are also reported. Figure 6.2 shows an example of a load-deflection diagram that was recorded using ASTM C1609/C1609M and the various parameters reported. ASTM C1399 may be used to determine the average residual strength of a FRS beam specimen. The beam is cracked in a controlled manner, then the load-versus-deflection curve is generated. Residual loads are determined and averaged at specified deflections, and the strength after cracking is reported. 6.3.3 Other methods 6.3.3.1 Density, boiled absorption, and permeable voids— ASTM C642 is typically used to determine the density,

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absorption, and permeable voids of FRS. Determining these characteristics provides an indication of the quality of the materials and application of FRS. 6.3.3.2 Explosive spall ing —EFNARC and others in Europe are developing a standard test method to assess the probability of explosive spalling of concrete and shotcrete when subjected to a high-temperature-rise fire, such as those fuelled by hydrocarbons. Many investigators use the Rijkswaterstaat (RWS) temperature-versus-time curve, which increases the furnace temperature from ambient to 2462 °F (1350 °C) in about 15 minutes, and then holds the temperature for 2 hours. The loss in FRS mass is then measured (TNO 1996).

CHAPTER 7—PERFORMANCE OF 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 the flexural strength of shotcrete. This postcrack performance is measured as energy absorbed after cracking. Two ASTM test methods were developed to measure the toughness of FRS. ASTM C1609/C1609M is a flexural beam test method that normally uses 4 x 4 x 14 in. (100 x 100 x 350 mm) specimens sawn from shot panels and tested on a 12 in. (300 mm) span in third-point loading. Net central beam deflections and loads are recorded and used to produce a load-deflection diagram. Postcracking loads are determined at specified deflections of span/600 and span/150, and converted to residual engineering strengths using elastic analysis. The total area under the load-deflection diagram is calculated using an end-point deflection of span/150, and reported as toughness (Fig. 6.2). ASTM C1550 is also a flexural test method developed using a round panel specimen 31.5 in. (800 mm) in diameter, 3 in. (75 mm) thick. The panel is supported symmetrically at three evenly spaced points at the perimeter and centrally loaded. Appropriate end-point deflections are selected based on the intended application. The net central deflections and loads are recorded and used to produce a load-deflection diagram. The area under the load-deflection diagram is integrated to produce an energy-versus-deflection curve that is used to evaluate the performance of FRS (Fig. 6.1). The beam test method has the advantage of resulting in material flexural strengths that can be used in engineering design and serviceability considerations as illustrated in Chapter 8. The difficulty in determining net deflections and using the required closed-loop, servo-controlled testing machines, and the inherent variability of beam flexural testing are disadvantages. The round panel test method has the advantage of low variability, and the fact that the test specimen is the shot-panel; thus, specimens do not have to be sawn from it, which eliminates a step. The disadvantage is that test results are reported in terms of energy (inch-pounds or Joules), which is not readily convenient for use by designers. Correlations between beam test results and panel test results are not valid (Bernard 2004). The beam tests are

thus used in normal practice to determine the residual strengths available from given fibers and dosages, while the round panel tests are used for quality control and assurance during construction.

7.2—Compressive strength The compressive strengths of FRS are not affected by the inclusion of fibers when using typical fiber contents of from 0.1 to 1% by volume. The mode of compressive failure may be changed from brittle to a more yielding failure, depending on 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 of fibers used , and the test method used to characterize shear strength, as is true for fiber-reinforced concrete (ACI 544.1R). Significant improvements in shear strength and shear toughness were reported by Mirsayah and Banthia (2002) for steel FRS, and improvements were also reported for 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 substrate and the age at testing. Because there are no standardized test methods to evaluate bond strength, many evaluations are conducted by drilling cylindrical cores through the shotcrete and substrate and pulling the two apart. The results of this evaluation are variable, and the method requires a number of core 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 greater percentage of steel fibers than aggregates rebound from the substrate. 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 drymix coarse aggregate mixtures shot onto vertical panels. In the Atlanta Research Chamber tests, the average rebound in a 10-minute test in which 2500 lb (1130 kg) of mixture was shot was 22% for a 3 in. (75 mm) thick dry-mix placement. The fiber content before shooting was 3.3% by mass of the dry material, while fiber content in the rebound material was 4.6% (Rose 1981). Tests have also indicated that steel fiber rebound is highly dependent on fiber geometry (Amelin and Banthia 1998a). An example of less rebound was reported for a trial in Nevada (Henager 1977) in which 4 yd 3 (3 m3) of steel fiber mixture consisting of 700 lb/yd 3 (415 kg/m 3) cement, 2700 lb/yd3 (1602 kg/m3) sand, and 150 lb/yd 3 (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 batch without fibers applied under identical conditions by the same personnel had an estimated rebound of 31%. The work was done in a tunnel, and included vertical and overhead surfaces.


For dry-mix shotcrete, Parker et al. (1975) reported average rebounds of 18.3 and 17.7% for a nonfibrous mixture and a fiber mixture, respectively, and concluded that the mere presence of fibers in a mixture does not affect rebound appreciably. Instead, other factors appear to be more important than fiber. Krantz (1984) stated, “Due to rebound, the effective amount of fibers is reduced to about only 50 to 70% of the amount in the mix in dry-mix shotcrete. For wet-mix shotcrete, the amount of fiber rebound is approximately 5 to 10%.” 7.5.2 Factors affecting rebound of fibers—Quantitative data on rebound of SFRS with the dry-process were obtained in a study that systematically investigated variables one at a time and used high-speed photography to observe the shotcrete airstream (Parker et al. 1975). The photography showed that many of the steel fibers were in the outer portion of the airstream, and that many of them were blown away radially from near the point of intended impact shortly before or after they hit. Some fibers were blown up into the air and floated down. It was obvious that the fibers were mostly blown away by the remnant air currents and that the effect was not one of fibers simply bouncing off the surface. When lower air pressure or less air was used, the amount and velocity of the remnant air currents was less, and the rebound of fiber was correspondingly less. Reducing air pressure or air volume, however, resulted in reduced in-place compaction. Banthia et al. (1992, 1994) present data on the effect of five steel fiber geometries on rebound and other shotcrete characteristics. They show ranges of fiber rebound for dryprocess of 35 to 78%, and wet-process of 12 to 18%. Very little is documented in the literature with respect to rebound of macrosynthetic fibers. The use of monofilament macrosynthetic fibers in wet-mix shotcrete applications has grown significantly worldwide since their introduction in the late 1990s. Unlike the stiffer steel fibers, which have to be used at relatively short lengths of approximately 1.2 in. (30 mm) to reduce line blockage, the more flexible macrosynthetic fibers can generally be used in well-proportioned wet-mix shotcrete mixtures at lengths ranging from 2 to 3 in. (50 to 75 mm) without significantly reducing the pumpability and shootability of the mixture. Due to excess fiber rebound and problems getting fibers through some dry-mix equipment, however, success in using macrosynthetic in drymix shotcrete is limited. Dufour et al. (2006) identified key parameters that affect the performance of monofilament macrosynthetic fiber in dry-mix shotcrete. Modifications were made to the geometrical characteristics of a specific fiber type to eliminate the problems observed and enable the production of high-quality macrosynthetic dry-mix FRS. It was shown that the rebound of both steel and macrosynthetic fibers at dosages of 75 and 11.6 lb/yd3 (45 and 6.9 kg/m3), respectively, was comparable with a mixture that contained silica fume when shot at the wettest stable plastic consistency. While the rebound of shotcrete for both mixtures containing steel and macrosynthetic fibers was 19.8 and 17.9%, respectively, of the total mass of shotcrete, it was

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determined that the fiber rebound of the total mass of fiber shot was 31.1 and 31.5%, respectively. 7.5.3 Conditions that reduce rebound —Parker et al. (1975) concluded that the rebound process differed during establishment of an initial critical thickness (Phase 1) and subsequent shooting onto fresh shotcrete (Phase 2). During Phase 1, anything that promotes adherence of material on the substrate should reduce rebound. This includes the following mixture conditions: a high cement content; more fines in the mixture (fly ash or very fine sand); smaller maximum size aggregate; proper wetness of aggregates so that particles are well-coated with cement; and a finer gradation. After initial critical thickness is established, Phase 2 rebound is reduced by any condition or set of conditions that makes the shotcrete on the substrate softer or more plastic, at least until it tends to drop off. Thus, for maximum reduction of Phase 2 rebound, shotcreting as wet as possible (that is, the wettest stable consistency) is one of the most beneficial and easiest conditions to control. A large number of measures can be used to reduce rebound of steel FRS in the dry process. The most effective of these measures (which also applies to nonfibrous shotcrete) seems to be reduction of the air pressure, air velocity, or amount of air at the nozzle; use of more fines and smaller aggregate; use of shorter, thicker fibers; predampening to get the correct moisture content; and shotcreting at the wettest stable consistency (Parker et al. 1975; Henager 1977).

7.6—Shrinkage crack control The 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 resistance to plastic shrinkage cracking due to excessive moisture loss 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 control crack widths at dosages as low as 0.25% by volume (Grzybowski and Shah 1990). When shotcrete is used in thin layers, and curing conditions may not be favorable, the use of fibers can mitigate potential cracking distress. One of the major problems with dry-process shotcrete is the high aggregate rebound. Further, large aggregate particles have a tendency to rebound as much as four times the rate of small particles (Amelin et al. 1997). This increases the cementitious content in the in-place shotcrete sometimes by as much as a factor of 2 (Amelin and Banthia 1998b). With very high cementitious contents and inadequate curing, early-age shrinkage cracking in dry-process shotcrete is a major concern. This is particularly true for high surfacevolume ratio placements such as repairs and lining elements where shotcrete is generally fully restrained, and large amounts of water may evaporate early on. Fiber reinforcement is one of the most effective ways of controlling plastic and drying shrinkage-induced cracking in dry-process shotcrete. Research results (Banthia and Campbell 1998) indicate that both steel and synthetic macrofibers are effective. Fibers not only delay the formation of cracks, but also reduce crack widths and total crack areas. The geometry

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impact tests were performed and comparisons were made with companion quasi-static tests. Both beams and plate specimens were tested. Results indicated that fiber reinforcement was highly effective in improving the fracture toughness under impact loading. Steel fibers were found to be the most effective, but the improvements depended on the geometry of the fiber. In the case of synthetic fibers, while polypropylene or polyvinyl alcohol macrofibers adequately improved the resistance of shotcrete to impact loads, pitch-based carbon microfibers were seen as relatively ineffective. Results further demonstrated that FRS is a highly strain-rate-sensitive material, and its fracture toughness under high rates of loading (such as those occurring under impact) is very different from its fracture toughness under quasi-static rates of loading. In some instances, FRS was seen to absorb less energy under impact loading than under quasi-static rates of loading.

7.8—Thermal explosive spalling Microfibers of polypropylene in shotcrete have demonstrated resistance to explosive spalling when subjected to hightemperature-rise fires, such as those fueled by hydrocarbons (Tatnall 2002). The fibers should have an equivalent diameter of less than 0.0013 in. (33 µm), and used in shotcrete tunnel linings at dosages of 1.6 to 3.4 lb/yd 3 (1 to 2 kg/m 3) for explosive spalling resistance (Tatnall 2002). Figure 7.1 shows shotcrete panels with and without microfibers subjected to fire testing. Fig. 7.1—Explosive spalling loss due to rapid temperaturerise heating from hydrocarbon fire.

of the fiber has a strong influence on its crack arrest capabilities. Excessive loss of fiber, however, may also occur through rebound in dry-process shotcrete, thereby diminishing the effectiveness of fiber reinforcement.

7.7—Impact resistance Shotcrete linings in rock stabilization and underground support construction in mines and tunnels are highly susceptible to impact loads caused by blasting or rock bursts. In deeper hard-rock mines, the high in-place and mininginduced stresses in the rock lead to rock bursts in the form of extensive, unstable rock fractures and rock-mass dilation that causes sudden ground movement in openings and drifts. Rock burst hazards increase as mines advance to greater depths, and high-quality ground support is required to minimize rock 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 impact resistance, failure may occur. Although nonmining shotcrete applications are possibly less vulnerable to impact loads, these may not be summarily ruled out. Fiber reinforcement of shotcrete is one of the most effective ways of increasing the impact resistance of shotcrete. In a large study at the University of British Columbia (Gupta et al. 2000; Banthia et al. 1999a,b,c,d), 10 different types of fibers were investigated for their effectiveness at enhancing the impact resistance of wet-process shotcrete. Instrumented

CHAPTER 8—DESIGN CONSIDERATIONS 8.1—General FRS has been used successfully for ground support for more than 25 years. Performance attributes are typically considered to be holding, retaining, and reinforcing. Although design with FRS and conventional shotcrete is basically the same, the material properties can be significantly different, thereby allowing considerable difference in shotcrete thickness and amount of reinforcement. Most available design data are for ground support, such as in tunnel linings. Simplistic and typically conservative analytical models have been developed from observation of shotcrete performance under service conditions and from large-scale testing 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 of them in other locales may not lead to adequate results because of changing geological and construction conditions. For more than 30 years, engineers have used rock mass classification systems such as rock mass rating (RMR) system and rock mass quality (Q) system to correlate shotcrete experience in differing ground conditions (Grimstad et al. 2002) These guidelines can be used to estimate shotcrete thickness, bid quantities, and support requirements during construction. Grant et al. (2001) presented a method to relate the empirically produced Barton chart (Grimstad and Barton 1993) to toughness values for SFRS based on a European test method. Papworth (2002) expanded the 2001 work to


include recommendations for FRS toughness values required based on ASTM C1550 tests using 1.6 in. (40 mm) central deflections for various values of rock quality, and deformations expected 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 reinforced shotcrete section to the moment capacity of an FRS section (Vandewalle 2005). In the conventionally reinforced section, the shotcrete is assumed cracked, and the welded wire reinforcement or reinforcing bars carry the entire tensile (flexural) load. The moment capacity may be calculated from Mo. CapConv. = φ AS f Y (d – a /2)

(8-1)

The moment capacity of an FRS section, which is assumed cracked, can be calculated from its residual strength as determined from the ASTM C1609/C1609M test results, and the section modulus of the FRS section, as follows 100

Mo. CapFRS = f 600 bt 2 /6

(8-2)

Setting the conventionally reinforced moment capacity equal to the FRS moment capacity, one can calculate the residual strength required, and, based on testing, determine the quantity of selected fibers required to provide the residual strength and, thus, the moment capacity required for comparable capacity of the FRS section (Vandewalle 1993). An example is illustrated in th e Appendix.

CHAPTER 9—SPECIFICATION AND QUALITY CONTROL CONSIDERATIONS 9.1—General Specifications for FRS should generally follow the recommendations found in ACI 506R and ACI 506.2 for shotcrete. Additional requirements should be added to specify the type or types (material) of fibers allowed, and either the performance criteria required or the type and quantity of fibers required. The user is cautioned that specification of a minimum dosage rate is not a guarantee of a minimum performance level. Specification of a performance level includes the synergistic effects of concrete flexural strength and fiber material, type, and dosage rate. Materials for FRS should meet the requirements of ASTM C1436. Materials for prepackaged, preblended, dry, combined shotcrete should meet the requirements of ASTM C1480/C1480M for Grade FR shotcrete.

9.2—Performance specifications If fibers are added to control plastic shrinkage cracking or to provide resistance to explosive spalling in fires, it is best to prescribe the type, size, and quantities of fibers required per cubic yard (cubic meter) of shotcrete. Macrofibers are normally used to increase the toughness and residual strength of the shotcrete in flexure, not the compressive strength nor the ultimate flexural strength (modulus of rupture). The specifier should establish criteria, in addition

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to the required compressive and flexural strengths, for the residual strength(s) required. Typically in specifications for ground support, 7-day flexural and residual strengths are required. For conditions where small deformations of the shotcrete are expected and minimum limits on crack width are required, the specifier should consider a residual strength 100 at small deflection, such as f 600 , which is the residual strength at 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 and crack widths are not as critical in the structure, then a residual strength should be specified at a larger beam deflection, such as 100 150 , which is the residual strength at a deflection of span/ 150, or 0.078 in. (2.0 mm). Typical residual strength values 100 specified for ground support FRS are f 600 ≥ 50% of the 100 modulus of rupture, and 150 ≥ 30% of the modulus of rupture. The 1.6 in. (40 mm) end-point deflection value in ASTM C1550 was chosen to evaluate crack widths primarily associated with mining applications. A smaller deflection, such as 0.27 to 0.39 in. (7 to 10 mm), should be used when specifying 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 the designer and specifier have knowledge of the performance of the specific fiber and dosage specified. If this type specification is used, guidance should be provided for utilization of alternative fibers and dosages.

CHAPTER 10—APPLICATIONS 10.1—General Applications of FRS include slope stabilization projects, mining and tunneling ground support, dam repairs and upgrades, bridge superstructure repairs, and sealing unstable ground. Examples of some applications follow.

10.2—Ground support 10.2.1 Tunneling—A recent example of both macrofiber and microfiber reinforced shotcrete is the renovation completed in 2005 of the 1880s Weehawken Tunnel in New Jersey for use on the Hudson-Bergen Light R ail rapid transit system. The old brick-lined railroad tunnel through the Palisades was enlarged to handle the transit line and install a station halfway through the 4154 ft (1266 m) long tunnel. The 42 ft (12.8 m) diameter shaft for the station elevators and the running tunnel used steel fiber-reinforced shotcrete for initial support. The transition section between the 27 ft (8.2 m) wide tunnel and the 65 ft (19.8 m) wide station used steel FRS with micropolypropylene fibers for explosive spalling protection in case of fires in t he final lining (Garrett 2004; Tatnall 2007). Figures 10.1 and 10.2 show FRS applied in the Weehawken tunnel and the nearby Exchange Place tunnels. 10.2.2 Mining—Rispin et al. (2005) reported on the use of steel fibers in shotcrete in deep hard-rock mining in Ontario, Canada, where the use of SFRS and rock bolts serve as the ground support system and facilitate the use of robotic application of the shotcrete that keeps miners from working under unsupported rock (Fig. 10.3). Owners of the Perseverance

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

Fig. 10.3—Shooting with robotic arm holding nozzle.

advantages for using FRS, including costs, aesthetics, and schedule. Journeaux (2004) detailed the rock-slope stabilization of the historic King’s Bluff and the Weehawken Tunnel Portal in New Jersey using prepackaged, tinted dry-process SFRS. 10.2.3.2 Soil nailing—Ballou and Niermann (2002) and Smith et al. (1993) described techniques for using SFRS for soil nailing projects in the U.S.

10.3—Rehabilitation and repair

Fig. 10.2—Exchange Place final lining steel fiber-reinforced shotcrete.

Mine in Western Australia used macrosynthetic fibers in shotcrete with and without rock bolts for ground control in very poor rock with high deformation; the macrosynthetic FRS demonstrated strain-hardening capabilities after cracking (Clements and Bernard 2004). O’Donnell (2000) described the usage development of SFRS as the primary support system for 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, quicker and safer remediation work, increased stability of drill hole collars, and verification that 84 lb/yd 3 (50 kg/m3) of a 1.25 in. (30 mm) deformed steel fiber was an adequate fiber content for the deformations experienced in this mine. 10.2.3 Slope stabilization 10.2.3.1 Rock and earth slopes—Keienburg (2006) described the use of SFRS for stabilizing an open pit mine in South Africa. Ballou (2004) described rock-slope stabilization projects in the western U.S., and outlined some of the

Examples of repairs to structures include the ongoing repairs to berth facing at the Port of Saint John, NB (Gilbride et al. 2002), where SFRS was used to rebuild deteriorated concrete berths at a port that experiences 33 ft (10 m) sea tides that cause many cycles of wetting and drying and freezing and thawing (Fig. 10.4). Experience at this port since 1982 with using steel fiber-reinforced concrete and shotcrete shows that the steel fibers do not corrode, even in this severe environment, except for the first few tenths of an inch (millimeters) after many years of service. Repairs to berths, wharves, and dolphins using microsynthetic fibers in the Caribbean are described by Hutter et al. (2007), and the repairs to the Pointe de la Prairie Lighthouse in Québec won the American Shotcrete Association Outstanding Repair and Rehabilitation Award (Giroux and Reny 2006). In 1994, a 4 in. (100 mm) thick bonded overlay of SFRS was used to stiffen the arches of the Littlerock Dam in Southern California in a seismic retrofit project. Forrest et al. (2004) outline many details of this project, including the design basis, preparation, quality control and assurance procedures, mixture proportions, and application procedures.

10.4—Architectural shotcrete Garshol (2000) described the use of steel FRS to build a 36 ft (11 m) tall troll at an amusement park in Norway. In 1999, a series of concrete lions on the Centre Street Bridge in Calgary, AB were rehabilitated using prepackaged microfiber-reinforced shotcrete (Kroman et al. 2002).


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C231

Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method

C293

Test Method for Flexural Strength of Concrete (Using Simple Beam with CenterPoint Loading)

C642

Test Method for Density, Absorption, and Voids in Hardened Concrete

C1116/C1116M Specification for Fiber-Reinforced Concrete C1140

Practice for Preparing and Testing Specimens from Shotcrete Test Panels

C1399 Fig. 10.4—Shooting berth faces on rising tide at Port of Saint John, NB, Canada.

Test Method for Obtaining Average Residual-Strength of Fiber-Reinforced Concrete

C1436

Specification for Materials for Shotcrete

10.5—Explosive spalling resistance

C1480/C1480M Specification for Packaged, Pre-Blended, Dry, Combined Materials for Use in Wet or Dry Shotcrete Application

Due to a number of extreme fires in highway and rail tunnels and the resulting damage to concrete and shotcrete linings, many new tunnels are using low dosages (1.6 to 5 lb/yd 3 [1 to 3 kg/m3]) of micropolypropylene fibers to resist explosive spalling of shotcrete. Examples include the Weehawken Tunnel 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 the Bindermichl tunnel Linz and the U2/U5 tunnel in Vienna, Austria (Winterberg and Dietze 2004).

CHAPTER 11—REFERENCES 11.1—Referenced standards and reports The standards and reports listed below were the latest editions at the time this document was prepared. Because these documents are revised frequently, the reader is advised to contact the proper sponsoring group if it is desired to refer to the latest version. American Concrete Institute 506R Guide to Shotcrete 506.2 Specifications for Shotcrete 544.1R Report on Fiber Reinforced Concrete 544.2R Measurement of Properties of Fiber Reinforced Concrete 544.3R Guide for Specifying, Proportioning, and Production of Fiber-Reinforced Concrete ASTM International C42/C42M Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete C78 Test Method for Flexural Strength of Concrete (Using Simple Beam with ThirdPoint Loading) C138/C138M Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete C143/C143M Test Method for Slump of HydraulicCement Concrete C173/C173M Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method

C1550

Test Method for Flexural Toughness of Fiber Reinforced Concrete (Using Centrally Loaded Round Panel)

C1583/C1583M Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pulloff Method) C1604/C1604M Test Method for Obtaining and Testing Drilled Cores of Shotcrete C1609/C1609M Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam with Third-Point Loading) Japan Concrete Institute

JCI-SF 5 Method of Test for Compressive Strength and Compressive Toughness of Fiber Reinforced Concrete JCI-SF 6 Method of Test for Shear Strength of Fiber Reinforced Concrete These publications may be obtained from these organizations: American Concrete Institute P.O. Box 9094 Farmington Hills, MI 48333-9094 www.concrete.org ASTM International 100 Barr Harbor Dr. West Conshohocken, PA 19428-2959 www.astm.org Japan Concrete Institute Mubanchi, Yotsuya 1-chrome, Shinjuku-ku Tokyo 160, Japan www.jsce.or.jp

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11.2—Cited references Amelin, H. S.; Banthia, N.; Morgan, D. R.; and Steeves, C., 1997, “Rebound in Dry-Mix Shotcrete,” Concrete International , V. 19, No. 9, Sept., pp. 54-60. Amelin, H. S., and Banthia, N., 1998a, “Steel Fiber Rebound in Shotcrete: Influence of Fiber Geometry,” Concrete International, V. 20, No. 9, Sept., pp. 74-79. Amelin, H. S., and Banthia, N., 1998b, “Mechanics of Aggregate Rebound in Shotcrete (Part 1),” Materials and Structures, RILEM, V. 31, Mar., pp. 91-98. Ballou, M., 2004, “Steep Slope Stabilization with FiberReinforced Shotcrete,” Shotcrete, V. 6, No. 4, Fall, pp. 12-14. Ballou, M., and Niermann, M., 2002, “Soil and Rock Slope Stabilization Using Fiber-Reinforced Shotcrete in North America,” Shotcrete, V. 4, No. 3, pp. 20-23. Banthia, N., and Campbell, K., 1998, “Restrained Shrinkage 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, “Impact Resistance 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, “Impact Resistance of Fiber Reinforced Wet-Mix Shotcrete, Part 2: Plate Tests,” Material s 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: Beam Tests,” 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: Plate Tests,” 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-Reinforced Wet-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 Requirements for 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 of Macro-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 MacroSynthetic Fibres in Dry-Mix Shotcrete,” Proceedings, Shotcrete for Underground Support X, D. R. Morgan and H. W. Parker, eds., Whistler, BC, Canada, Sept., pp. 194-205. EFNARC, 1996, “European Specification for Sprayed Concrete,” European Federation of Producers and Applicators of 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 of Littlerock Dam,” Shotcrete, V. 6, No. 1, Winter, pp. 20-26.

Garrett, R., 2004, “Construction Chemistry at Weehawken,” 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 Tidal Zones at the Port of Saint John,” Shotcrete, V. 4, No. 4, Fall, pp. 32-38. Giroux, P., and Reny, S., 2006, “2005 Outstanding Repair Project: 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 Engineering Developments in Shotcrete, Hobart, Tasmania, Australia, E. S. Bernard, ed., Apr., pp. 111-118. Grimstad, E., and Barton, N., 1993, “Updating of the QSystem for NMT,” Proceedings, International Symposium on Sprayed 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 in Designing Reinforced Ribs of Sprayed Concrete and Energy Absorption,” Proceedings, Fourth International Symposium on Sprayed Concrete—Modern Use of Wet-Mix Sprayed Concrete for Underground Support, Davos, Switzerland, Norwegian Concrete Association, Oslo, Sept., pp. 134-155. Grzybowski, M., and Shah, S. P., 1990, “Shrinkage Cracking in Fiber Reinforced Concrete,” ACI Materials Journal, V. 87, No. 2, Mar.-Apr., pp. 138-148. Gupta, P.; Banthia, N.; and Yan, C., 2000, “Fiber Reinforced Wet-Mix Shotcrete under Impact,” Journal of Materials in Civil 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 Steel Fibrous Shotcrete: A State-of-the-Art Report , Battelle-Northwest, Richland, WA, Sept., 60 pp. Hutter, J.; Dufour, J.-F.; and Fullam, N., 2007, “Shotcrete Repairs in Barbados—A Caribbean Experience,” Shotcrete, V. 9, No. 1, Winter, pp. 10-14. Journeaux, D., 2004. “Rock Stabilization of Two Historic ally Sensitive Rock Slopes Using Shotcrete,” Shotcrete, V. 6, No. 2, Spring, pp. 10-13. Kaden, R. A., 1977, “Fiber Reinforced Shotcrete: Ririe Dam and Little Goose (CPRR) Relocation,” Shotcrete for Ground Support , SP-54, American Concrete Institute/American Society of Civil Engineers, Farmington Hills, MI, pp. 66-88. Keienburg, M., 2006, “Slope Stabilization in an Open Pit Mine,” Shotcrete, V. 8, No. 3, Summer, pp. 28-30. Krantz, G. W., 1984, “Selected Pneumatic Gunites for Use in Underground Mining: A Comparative Engineering Analysis,” 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.


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 Fiber Matrix,” Canadian Journal of Civil Engineering , V. 33, No. 6, June, pp. 726-734. Mirsayah, A., and Banthia, N., 2002, “Shear Strength of Steel Fiber Reinforced Concrete,” ACI Ma terials Journal , V. 99, No. 5, Sept.-Oct., pp. 473-479. Morgan, D. R., and Heere, R., 2000, “Evolution of Fiber Reinforced Shotcrete,” Shotcrete, V. 2, No. 2, May, pp. 8-11. O’Donnell, J. D. P., 2000, “Shotcrete: A Key to Advances in Safety and Productivity in Mining,” Shotcrete, V. 2, No. 3, Aug., pp. 20-22. Padron, I. and Zollo, R. F., 1990, “Effect of Synthetic Fibers on Volume Stability and Cracking or Portland Cement Concrete and Mortar,” ACI Materials Journal, V. 87, No. 4, July-Aug., pp. 327-332. Papworth, F., 2002, “Design Guidelines for the Use of Fiber-Reinforced Shotcrete in Ground Support,” Shotcrete, V. 4, No. 2, Spring, pp. 16-21. Parker, H. W., 1974, “Current Field Research Program on Shotcrete,” Proceedings, Use of Shotcrete for Underground Support, SP-45, ASCE, pp. 330-350. Parker, H. W.; Fernandez, G.; and Loring, L. J., 1975, “Field-Oriented Investigation of Conventional and Experimental Shotcrete for Tunnels,” Report No. FRA-OR&D 76-06, Federal Railroad Administration, Washington, DC, Aug., 628 pp. Poad, M. E.; Serbousek, M. O.; and Goris, J. , 1975, “Engineering Properties of Fiber-Reinforced and PolymerImpregnated Shotcrete,” Report of Investigations No. 8001, U.S. Bureau of Mines, Washington, DC, 25 pp. Rispin, M.; Gause, C.; and Kurth, T., 2005, “Robotic Shotcrete Applications for Mining and Tunneling,” Shotcrete, V. 7, No. 3, Summer, pp. 4-9. Rose, D., 1981, “The Atlanta Research Chamber, Applied Research for Tunnels: Blasting Techniques Conventional Shotcrete Steel-Fiber-Reinforced Shotcrete Monographs on the State-of-the-Art of Tunneling,” Report No. UMTA-GA06-0007-81-1, U.S. Department of Transportation, Washington, DC, Mar., 535 pp. Ryan, T. F., 1975, “Steel Fibers in Gunite, An Appraisal,” Tunnels and Tunnelling (London), July, pp. 74-75. Sandell, B., 1977, “Steel Fiber Reinforced Shotcrete (Stalfiberarmerad Sprubeton),” Proceedings, Informations-Dagen 1977, Cement-Och Betonginstitutet, Stockholm, pp. 50-75. Smith, R. E.; Pearlman, S. L.; and Wolosick, J. R., 1993, “Soil Support Using Steel Fiber Reinforced Shotcrete: A Few Case Histories,” Proceedings, Shotcrete for Underground Support VI, Engineering Foundation Conference, Niagara-on-the-Lake, ON, Canada, May 2-6, 11 pp. Spirig, C., 2004, “Sprayed Concrete Systems in the Gotthard Base Tunnel,” Proceedings, Second International Conference on Engineering Developments in Shotcrete, Cairns, Queensland, Australia, E. S. Bernard, ed., Taylor and Francis Group, Oct., pp. 245-249.

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Talbot, C.; Talbot, C.; Pigeon, M.; Beaupré, D.; and Morgan, D. R., 1994, “Influence of Surface Preparation on Long-Term Bonding of Shotcrete,” ACI Materials Journal, V. 91, No. 6, Nov.-Dec., pp. 560-566. Tatnall, P. C., 2002, “Shotcrete in Fires: Effects of Fibers on Explosive Spalling,” Shotcrete, V. 4, No. 4, Fall, pp. 10-12. Tatnall, P. C., 2007, “U.S. Standards Update,” Shotcrete Corner, Shotcrete, V. 9, No. 2, Spring, pp. 36-38. TNO, 1996, “The Netherlands Organization for Applied Scientific Research,” TNO, Postbus 49, 2600 AA Delft, The Netherlands, www.nitg.tno.nl/eng. Vandewalle, M., 1993, “Steel Fibre Reinforced Shotcrete Design,” Proceedings , Shotcrete for Underground Support VI, Engineering Foundation Conference, Niagara-on-theLake, ON, Canada, May 2-6, pp. 99-109. Vandewalle, M., 2005, Tunnelling is an Art , N.V. Bekaert, S.A., Zwevegem, Belgium, 400 pp. Winterberg, R., and Dietze, R., 2004, “Efficient Passive Fire Protection Systems for High Performance Shotcrete,” Proceedings, Second International Conference on Engineering Developments in Shotcrete, Oct. 4, Cairns, Queensland, Australia, E. S. Bernard, ed., Taylor and Francis Group, pp. 275-290.

APPENDIX—EXAMPLE OF COMPARABLE MOMENT CAPACITY CALCULATION Chapter 8 discusses design considerations, and Section 8.3 provides a method and equations for comparing the moment capacity of a conventionally reinforced shotcrete section to that of an FRS section. An example of these calculations is presented 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 with one layer of 4 x 4 x W4.0/W4.0 WWR (102 x 102-MW26 x MW26). The welded wire reinforcement is assumed in the center of the shotcrete lining. The yield strength of the welded wire reinforcement, f Y , is 65,000 lbf/in.2 (448.3 MPa). What is the post-cracking residual flexural strength required for a comparable fiber-reinforced shotcrete section? Inch-pound units Using Eq. (8-1): b = unit width = 12 in. (1 ft) AS = area of c onventional reinforcing per unit width AS = 0.04 in. 2 × 12 in./4 in. = 0.12 in. 2 /ft f Y = 65,000 lbf/in. 2 f c′ = 5000 lbf/in. 2 a = AS f Y / 0.85 f c′ b 2

0.12 in. × 65,000 psi a = --------------------------------------------------------0.85 × 5000 psi × 12 in.

SI units b=1m

AS = 26 mm 2 × 1000 mm/102 mm = 254.9 mm2 /m f Y = 448.3 N/mm 2 f c′ = 34.5 N/mm2 2

2

254.9 mm × 448.3 N/mm a = --------------------------------------------------------------------------2 0.85 × 34.5 N/mm × 1000 mm

a = 0.153 in. t = section thickness = 4 in. d = t /2 = 4 in./2 = 2 in.

a = 3.897 mm t = 102 mm d = 102 mm/2 = 51 mm

Mo. CapConv = φ AS f Y (d – a /2) Mo. CapConv = 0.9 × 0.12 × 65,000 × (2 – 0.153/2) Mo. CapConv = 13,503 in.-lb/ft

= 0.9 × 254.9 × 448.3 × (51 – 3.897/2) = 5,044,677 N-mm = 5.045 kN-m

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Using Eq. (8-2): 100 Determine 600 , residual strength required: Mo. CapFRS =

100 600

× b × t 2 /6

100

f 600 = 6 × Mo. Cap/ b × t 2, where Mo. Cap. is that of the conventional reinforcing. 100

f 600 = 6 × 13,503 in.-lb/ft/ 12 in./ft × 4 2 in.2 = 422 lbf/in. 2

= 6 × 5.045 kN-mm × 1000 mm/m/ 1 m × 1022 mm2 = 2.91 N/mm2

Thus, a 4 in. (102 mm) thick FRS lining with a postcrack residual flexural strength of 422 psi (2.91 MPa) as determined 100 at 0.02 in. (0.5 mm) deflection ( 600 ) using ASTM C1609/ C1609M will provide comparable moment capacity to the conventionally reinforced lining.

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