Introduction to Shotcrete Applications Course No: C04-002

Credit: 4 PDH

Gilbert Gedeon, P.E.

Continuing Education and Development, Inc. 9 Greyridge Farm Court Stony Point, NY 10980 P: (877) 322-5800 F: (877) 322-4774 info@cedengineering.com

CECW-EG

Engineer Manual

1110-2-2005

Department of the ArmyU.S. Army Corps of Engineers

Washington, DC 20314-1000

EM 1110-2-2005

31 January 1993

Engineering and Design

STANDARD PRACTICE FOR SHOTCRETE

Distribution Restriction StatementApproved for public release; distribution is

unlimited.

EM 1110-2-200531 January 1993

US Army Corpsof Engineers

ENGINEERING AND DESIGN

Standard Practice for Shotcrete

ENGINEER MANUAL

DEPARTMENT OF THE ARMY EM 1110-2-2005US Army Corps of Engineers

CECW-EG Washington, DC 20314-1000

Engineer ManualNo. 1110-2-2005 31 January 1993

Engineering and DesignSTANDARD PRACTICE FOR SHOTCRETE

1. Purpose. This manual provides information and guidance on the selection, proportioning, andapplication of shotcrete as a construction material.

2. Applicability. This manual applies to all HQUSACE/OCE elements, major subordinate commands,districts, laboratories, and field operating activities (FOA) having civil works responsibilities.

3. Discussion. This manual describes general construction procedures using shotcrete. It includesboth the dry-mix process, in which most of the mixing water is added at the nozzle and the wet-mixprocess, in which all of the materials are mixed before entering the delivery hose. Additionalinformation on concrete properties and mixing proportioning are available in EM 1110-2-2000,"Standard Practice for Concrete."

FOR THE COMMANDER:

WILLIAM D. BROWNColonel, Corps of EngineersChief of Staff

This manual supersedes EM 1110-2-2005, dated 10 September 1982.

DEPARTMENT OF THE ARMY EM 1110-2-2005US Army Corps of Engineers

CECW-EG Washington, DC 20314-1000

Engineer ManualNo. 1110-2-2005 31 January 1993

Engineering and DesignSTANDARD PRACTICE FOR SHOTCRETE

Table of Contents

Subject Paragraph Page Subject Paragraph Page

Chapter 1IntroductionPurpose . . . . . . . . . . . . . . . . . . . . . 1-1 1-1Applicability . . . . . . . . . . . . . . . . . . 1-2 1-1References . . . . . . . . . . . . . . . . . . . 1-3 1-1Glossary . . . . . . . . . . . . . . . . . . . . . 1-4 1-1Background. . . . . . . . . . . . . . . . . . . 1-5 1-1Activities and Documentation. . . . . . 1-6 1-1Point of Contact . . . . . . . . . . . . . . . 1-7 1-2

Chapter 2Types of Shotcrete and ApplicationsWhy Shotcrete. . . . . . . . . . . . . . . . . 2-1 2-1Applications . . . . . . . . . . . . . . . . . . 2-2 2-1Shotcrete Processes. . . . . . . . . . . . . 2-3 2-2Fiber-Reinforced Shotcrete. . . . . . . . 2-4 2-4Silica-Fume Shotcrete. . . . . . . . . . . . 2-5 2-4Polymer-Modified Shotcrete. . . . . . . 2-6 2-4Accelerated Shotcrete. . . . . . . . . . . . 2-7 2-5

Chapter 3Materials, Proportioning,and PropertiesCementitious Materials. . . . . . . . . . . 3-1 3-1Aggregate. . . . . . . . . . . . . . . . . . . . 3-2 3-2Water . . . . . . . . . . . . . . . . . . . . . . . 3-3 3-2Chemical Admixtures. . . . . . . . . . . . 3-4 3-2Reinforcing Stee1 . . . . . . . . . . . . . . 3-5 3-3Fiber Reinforcement. . . . . . . . . . . . . 3-6 3-4Proportioning Shotcrete. . . . . . . . . . 3-7 3-4Properties of Shotcrete. . . . . . . . . . . 3-8 3-6

Chapter 4Equipment and CrewGeneral Equipment . . . . . . . . . . . . . 4-1 4-1Dry-Mix Process . . . . . . . . . . . . . . . 4-2 4-1Wet-Mix Process. . . . . . . . . . . . . . . 4-3 4-1Auxiliary Equipment . . . . . . . . . . . . 4-4 4-1Special Equipment. . . . . . . . . . . . . . 4-5 4-7Crew Composition. . . . . . . . . . . . . . 4-6 4-7

Chapter 5Preconstruction Testingand EvaluationGeneral. . . . . . . . . . . . . . . . . . . . . . 5-1 5-1Nozzleman Certification. . . . . . . . . . 5-2 5-1Mixture Proportioning Evaluation . . . 5-3 5-1Preconstruction Demonstration and

Testing . . . . . . . . . . . . . . . . . . . . . 5-4 5-1Alternate Considerations. . . . . . . . . . 5-5 5-6

Chapter 6PlacementPreparations . . . . . . . . . . . . . . . . . . 6-1 6-1Batching and Mixing . . . . . . . . . . . . 6-2 6-2Shotcrete Application

Techniques. . . . . . . . . . . . . . . . . . 6-3 6-3Rebound. . . . . . . . . . . . . . . . . . . . . 6-4 6-8Finishing . . . . . . . . . . . . . . . . . . . . 6-5 6-8Curing and Protection. . . . . . . . . . . . 6-6 6-9Repair of Surface Defects. . . . . . . . . 6-7 6-9

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Subject Paragraph Page

Chapter 7Quality ControlGeneral Considerations. . . . . . . . . . . 7-1 7-1Preproduction Phase. . . . . . . . . . . . . 7-2 7-1Production Phase. . . . . . . . . . . . . . . 7-3 7-2Corrective Actions. . . . . . . . . . . . . . 7-4 7-4

Chapter 8Quality AssuranceGeneral Considerations. . . . . . . . . . . 8-1 8-1Preproduction Phase. . . . . . . . . . . . . 8-2 8-1Production Phase. . . . . . . . . . . . . . . 8-3 8-1

Appendices

Appendix AReferences

Appendix BGlossary

Appendix CCorps of Engineers Projects

Appendix DMixture Proportioning SampleSubmittal

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Chapter 1Introduction

1-1. Purpose

This manual provides information and guidance on theselection, proportioning, and application of shotcrete. Itis intended for use by engineers and technical stafftasked with the planning, design, contract preparation,and construction management phases of a shotcreteproject. A quality assurance chapter is included whichdetails necessary technical activities during theconstruction phase. Subjects discussed include shotcreteand applications, materials, equipment and crew,preconstruction testing and evaluation, placement, qualitycontrol, and quality assurance. This manual does notprovide guidelines for structural analysis of shotcreteapplications. Refer to EM 1110-2-2000 for additionalgeneral guidance on concrete.

1-2. Applicability

This manual is applicable to all HQUSACE/OCEelements, major subordinate commands, districts,laboratories, and field operating activities (FOA) havingcivil works responsibilities.

1-3. References

Appendix A consists of a list of cited references thatappear in the body of the text as well as a selectedbibliography pertaining to the use of shotcrete. Thereader is encouraged to study applicable references tosupplement the guidance provided by this manual. Inparticular, the reader is encouraged to refer to AmericanConcrete Institute (ACI) Committee Report 506R-90,"Guide to Shotcrete" (paragraph A-1, ACI (1991d)), andother ACI 506 documents (paragraph A-1, ACI (1991e),paragraph A-2, ACI (1991c and 1991d)).

1-4. Glossary

Appendix B consists of definitions of terms commonlyused in shotcrete.

1-5. Background

a. Special equipment and techniques.Equipment forpneumatically applying a fine aggregate cement mixturewas first introduced in 1910. Since that time, manyimprovements have been made in the equipment and inthe specialized techniques required for application of

pneumatically applied mortar or concrete. The wideacceptance of shotcrete for slope and surface protection,swimming pool construction, tunnel lining, specialarchitectural features, and renovating existing structureshas resulted in the availability of a wide variety ofmanufactured pneumatic placement equipment.

b. Shotcrete denotes various mixtures.Shotcrete hasbeen referred to by such terms as Gunite, formerly atradename for pneumatically applied mortar or concrete,sprayed concrete, spraycrete, air-blown mortar andconcrete, gunned concrete, and others. In some areas"gunite" has been used to denote small-aggregateshotcrete and mortar mixtures, and "shotcrete" to denotelarge-aggregate mixtures. The preferred term today forall gunned material is shotcrete, regardless of theaggregate size.

c. Specialty shotcretes.While most shotcrete placedis the traditional dry-mix and wet-mix shotcrete, the useof specialty shotcretes has become common. Theaddition of accelerators, fibers, and silica fume canprovide shotcrete with significantly enhancedperformance.

d. Varied applications. Typical applications forCorps of Engineers (Corps) projects further discussed inChapter 2 include slope protection and stabilization,temporary excavation protection, tunnel support, andvarious structural and remedial applications. Appendix Cprovides a listing of some Corps projects that have usedshotcrete for various applications.

1-6. Activities and Documentation

Involvement in shotcrete activities ranges frompreliminary planning studies through the engineering anddesign phases, preparation of contract documents, toconstruction management. During these activities theengineer or other professional must performinvestigations, prepare documents, and review designrequirements. These activities often result in theproduction of the following documents:

- Shotcrete Investigation Report- Technical Specifications- Engineering Considerations and Instructions for

Field Personnel

a. Shotcrete investigation report.The informationlisted is to be included in a shotcrete investigation reportand prepared either as a separate report or part of adesign memorandum, as a preparatory step to the

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production of technical specifications. The formalizationof such a report depends on the size and complexity ofthe shotcrete project.

(1) Shotcrete quantity to be used and qualityrequired.

(2) Climatic and service conditions to which theshotcrete will be subjected.

(3) Types of shotcrete processes and deliveryequipment to be used.

(4) Types, kinds, and sources of cementitiousmaterials to be specified, including special requirements.

(5) Potential aggregate sources, quality, andconstituents.

(6) Grading of aggregate to be specified.

(7) Types and kinds of admixtures to be specified,including test requirements.

b. Technical specifications.Civil Works GuideSpecification CW 03361 provides a basis for preparationof a specification for shotcrete.

c. Engineering considerations and instruction forfield personnel. In accordance with EM 1110-2-2000,the designer should provide explanation of the intent ofthe shotcrete application, special precautions, criticalitems to monitor, and any other information that may bebeneficial to the field staff.

1-7. Point of Contact

Questions or discussion concerning this manual should bedirected through Headquarters, US Army Corps ofEngineers, ATTN: CECW-EG.

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Chapter 2Types of Shotcrete andApplications

2-1. Why Shotcrete

a. Importance of proper application. Properlyapplied shotcrete is a structurally sound and durableconstruction material which exhibits excellent bondingcharacteristics to existing concrete, rock, steel, and manyother materials. It can have high strength, lowabsorption, good resistance to weathering, and resistanceto some forms of chemical attack. Many of the physicalproperties of sound shotcrete are comparable or superiorto those of conventional concrete or mortar having thesame composition. Improperly applied shotcrete maycreate conditions much worse than the untreatedcondition.

b. Advantages of shotcrete.Shotcrete is used in lieuof conventional concrete, in most instances, for reasonsof cost or convenience. Shotcrete is advantageous insituations when formwork is cost prohibitive orimpractical and where forms can be reduced oreliminated, access to the work area is difficult, thinlayers or variable thicknesses are required, or normalcasting techniques cannot be employed. Additionalsavings are possible because shotcrete requires only asmall, portable plant for manufacture and placement.Shotcreting operations can often be accomplished inareas of limited access to make repairs to structures.

c. Strength of bonding. The excellent bonding ofshotcrete to other materials is often an important designconsideration. The force of the impact of thispneumatically propelled material on the surface causescompaction of the shotcrete paste matrix into the finesurface irregularities and results in good adhesion to thesurface. Within limits, the material is capable ofsupporting itself in vertical or overhead applications.

2-2. Applications

The selection of shotcrete for a particular applicationshould be based on knowledge, experience, and a carefulstudy of required and achievable material performance.The success of the shotcrete for that application iscontingent upon proper planning and supervision, plusthe skill and continuous attention provided by theshotcrete applicator. The following paragraphs discuss

the use of shotcrete in several of the more commonapplications. A number of shotcrete applications by theCorps of Engineers are listed in Appendix C.

a. Repair. Shotcrete can be used to repair thedamaged surface of concrete, wood, or steel structuresprovided there is access to the surface needing repair.The following examples indicate a few ways in whichshotcrete can be used in repairs:

(1) Bridges. Shotcrete repair can be used for bridgedeck rehabilitation, but it has generally beenuneconomical for major full-thickness repairs. It is veryuseful, however, for beam repairs of variable depths,caps, columns, abutments, wingwalls, and underdecksfrom the standpoint of technique and cost.

(2) Buildings. In building repairs, shotcrete iscommonly used for repair of fire and earthquake damageand deterioration, strengthening walls, and encasingstructural steel for fireproofing. The repair of structuralmembers such as beams, columns, and connections iscommon for structures damaged by an earthquake.

(3) Marine structures. Damage to marine structurescan result from deterioration of the concrete and of thereinforcement. Damaging conditions are corrosion of thesteel, freezing and thawing action, impact loading,structural distress, physical abrasion from the action ofwaves, sand, gravel, and floating ice, and chemical attackdue to sulfates. These problems can occur in mostmarine structures such as bridge decks, piles, pile caps,beams, piers, navigation locks, guide walls, dams,powerhouses, and discharge tunnels. In many cases,shotcrete can be used to repair the deteriorated surfacesof these structures.

(4) Spillway surfaces. Surfaces subject to high-velocity flows may be damaged by cavitation erosion orabrasion erosion. Shotcrete repairs are advantageousbecause of the relatively short outage necessary tocomplete the repairs.

b. Underground excavations.For the most part,shotcrete is used in underground excavations in rock; buton occasion, it has been successfully used in theadvancement of tunnels through altered, cohesionless, andloose soils. Typical underground shotcrete applicationsrange from supplementing or replacing conventionalsupport materials such as lagging and steel sets, sealingrock surfaces, channeling water flows, and installingtemporary support and permanent linings.

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c. Slope and surface protection.Shotcrete is oftenused for temporary protection of exposed rock surfacesthat will deteriorate when exposed to air. Shotcrete isalso used to permanently cover slopes or cuts that mayerode in time or otherwise deteriorate. Slope protectionshould be properly drained to prevent damage fromexcessive uplift pressure. Application of shotcrete to thesurface of landfills and other waste areas is beneficial toprevent surface water infiltration.

d. New structures.Shotcrete is not necessarily thefastest method of placing concrete on all jobs, but wherethin sections and large areas are involved, shotcreting canbe used effectively to save time. The followingparagraphs describe some of the applications involvedwith construction of new structures.

(1) Pools and tanks. Shotcrete has been usedextensively to construct concrete swimming pools. Morerecently, large aquariums have been constructed usingshotcrete.

(2) Shotcrete floors and walls. Shotcrete floors intanks and pools on well compacted subbase or onundisturbed earth have generally given excellent service.Vertical and overhead construction for walls, slabs,columns, and other structural members has beenfrequently shotcreted.

(3) Shotcrete domes. Construction techniques usinginflatable air-forming systems have made the constructionof shotcrete shells or domes practical. These largestructures have been used for residential housing,warehousing, bridge, and culvert applications.

2-3. Shotcrete Processes

Shotcrete can be applied by two distinct applicationtechniques, the dry-mix process and the wet-mix process.

a. Dry-mix shotcrete.The cementitious material andaggregate are thoroughly mixed and either bagged in adry condition, or mixed and delivered directly to the gun.The mixture is normally fed to a pneumatically operatedgun which delivers a continuous flow of material throughthe delivery hose to the nozzle. The interior of thenozzle is fitted with a water ring which uniformly injectswater into the mixture as it is being discharged from thenozzle and propelled against the receiving surface.

b. Wet-mix shotcrete.The cementitious material,aggregate, water, and admixtures are thoroughly mixed aswould be done for conventional concrete. The mixedmaterial is fed to the delivery equipment, such as aconcrete pump, which propels the mixture through thedelivery hose by positive displacement or by compressedair. Additional air is added at the nozzle to increase thenozzle discharge velocity.

c. Comparison of dry-mix and wet-mixprocesses.Shotcrete suitable for most requirements canbe produced by either the dry-mix or wet-mix process.However, differences in the equipment cost, maintenancerequirements, operational features, placementcharacteristics, and product quality may make one or theother more attractive for a particular application. Acomparative summary of the advantages anddisadvantages of the processes is given in Table 2-1.

(1) Bond strengths of new shotcrete to existingmaterials are generally higher with dry-mix shotcretethan with wet-mix shotcrete. Both shotcrete mixturesoften provide significantly higher bond strengths toexisting materials than does conventional concrete.

(2) Typically, dry-mix shotcrete is applied at a muchslower rate than wet-mix shotcrete. Dry-mix shotcrete isoften applied at a rate of 1 or 2 cubic yards per hourcompared to wet-mix shotcrete applied at a rate of up to7 or 8 cubic yards per hour. Depending on the appli-cation, the in-place production rate may be significantlylower because of obstacles, rebound, and other featureswhich may cause delays.

(3) Rebound is the shotcrete material that "bounces"off the shooting surface. Rebound for conventionaldry-mix shotcrete, in the best of conditions, can beexpected to be at least 20 percent of the total materialpassed through the nozzle. Wet-mix shotcrete reboundssomewhat less than dry-mix shotcrete.

(4) The use of air-entraining admixtures (AEA) inshotcrete is practical only in wet-mix shotcrete. Whenbatched properly, AEA forms an air-void system suitablefor providing frost resistance to wet-mix shotcrete. Theformation of an air-void system in dry-mix shotcrete isnot possible. However, dry-mix shotcrete, when properlyproportioned and applied, will have a compressivestrength exceeding approximately 7,000 pounds per

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Table 2·1 Comparison of Features of Dry·Mix and Wet-Mix Shotcrete Processes

Dry-Mix Process Wet-Mix Process

Mixing water instantaneously controlled at the nozzle by operator to meet variable Mixing water controlled at plant and measured at time of batching. field conditions.

Longer hose lengths possible, if necessary. Normal pumping distances necessary.

Umited to accelerators as the only practical admixture. Compatible with all ordinary admixtures. Special dispensers for addition of accelerators are necessary.

Use of air-entraining admixture not beneficial. Resistance to freezing and thawing Air entrainment possible. Acceptable resistance to freezing and thawing. is poor.

Intermittent use easily accommodated within prescribed time limits. Best suited for continuous application of shotcrete.

Exceptional strength performance possible. Lower strengths, similar to conventional concrete.

Lower production rates. Higher production rates.

Higher rebound. Lower rebound.

Equipment maintenance costs tend to be lower. Equipment maintenance costs tend to be higher.

Higher bond strengths. Lower bond strengths, yet often higher than conventional concrete.

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square inch (psi). It has performed well in moderateexposures to freezing and thawing.

2-4. Fiber-Reinforced Shotcrete

a. Unreinforced shotcrete, like unreinforcedconventional concrete, is a brittle material thatexperiences cracking and displacement when subjected totensile stresses or strains. The addition of fibers to theshotcrete mixture adds ductility to the material as well asenergy absorption capacity and impact resistance. Thecomposite material is capable of sustaining postcrackloadings and often displays increased ultimate strength,particularly tensile strength. Fibers used in shotcrete areavailable in three general forms: steel fibers, glassfibers, and other synthetic fibers. Natural fiber, a fourthform, is not commonly used in shotcrete and will not bediscussed.

b. The use of steel fibers has evolved rapidly sinceits inception in the late 1950’s. The present third-generation steel fibers are greatly superior to the earlierfibers. Early mixing and handling problems whichhampered uniform distribution of fibers in a mixture havebeen minimized by the manufacture of fibers with low-aspect ratios (ratio of length to diameter), surfacedeformations, and improved shape.

c. The use of glass-fiber-reinforced shotcrete (GFRS)is an adaptation of the technology of using chopped glassfibers and a resin binder. The equipment and process toapply glass-fiber shotcrete is not a conventional shotcreteoperation, but requires a special gun and delivery system.This process termed "spray-up" is used extensively in theconstruction of lightweight panels for building claddingand special architectural features and is usually applied ina plant production situation. A common onsiteapplication is the construction of simulated rockstructures for animal exhibits at zoos. The fibers aremade from a special zirconium alkali-resistant (AR) glassto resist deterioration in the highly alkaline portland-cement environment. Guidelines for the use of glass-fiber spray-up are provided by the Prestressed ConcreteInstitute (PCI) (1981).

d. Other synthetic fibers are composed of nylon,polypropylene, polyethylene, polyester, and rayon. Thepredominant fiber used for shotcrete has been ofpolypropylene produced in a collated fibrillated form.The primary benefit of synthetic fiber additions toshotcrete is to decrease width of shrinkage cracks in thematerial.

e. Typical applications for fiber-reinforced shotcreteare for tunnel linings, surface coatings on rock and soil,slopes, structures, embankments, or other structures thatmay be subject to high deformations or where crackcontrol is needed.

2-5. Silica-Fume Shotcrete

a. Silica fume is a very fine noncrystallinepozzolanic material composed mostly of silica. Silicafume is used in concrete and shotcrete to increasestrength, decrease permeability, and enhance cohesionand adhesion. Specific advantages of silica fume inshotcrete are the improved bond strength of shotcrete tosubstrate surfaces, the improved cohesion of theshotcrete, and the resulting ability to apply thicker layersof shotcrete in a single pass to vertical and overheadsurfaces. The material is more resistant to "washout,"where fresh shotcrete is subject to the action of flowingwater, and rebound is significantly reduced. Shotcretecontaining silica fume may have improved resistance toaggressive chemicals.

b. In general, silica-fume shotcrete producesunhardened and hardened material properties which,among other uses, make it suitable as a substitute forpolymer-modified shotcrete and accelerated shotcreteapplications. Use of silica-fume shotcrete should beconsidered for many applications that presently useconventional shotcrete because of its bond and strengthperformance.

c. Silica-fume shotcrete has been widely used intunnel construction often combined with fibers to controlshrinkage cracking. Because of inherent improvementsin permeability, silica-fume shotcrete has been used tocap landfills and other waste areas to be sealed fromsurface water infiltration. Performance in high-strengthapplications is more easily accomplished with silica-fumeshotcrete.

2-6. Polymer-Modified Shotcrete

a. Polymers are incorporated into shotcrete in twoways. In one method, the entire binder is composed of apolymer material. This is no longer a hydraulic-cementproduct but a polymer shotcrete. The more common useof polymers is the addition of a polymer emulsion to thehydraulic-cement mixture, as with a partial replacementof the mixing water, or as total replacement, whichdisperses throughout the mixture forming a continuouspolymer matrix. This is termed polymer-portland-cementshotcrete.

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b. The emulsified polymer for use in shotcrete hasusually been styrene butadiene. Acrylic polymer latexesand epoxy resins are less frequently used products forportland-cement systems. The advantage of polymer-modified systems are that the polymers improve flexuraland tensile strengths, improve bond, and reduceabsorption because of lower permeabilities.

2-7. Accelerated Shotcrete

a. Accelerating admixtures are used extensively inshotcrete. Highly effective accelerators have beendeveloped for rapid setting of shotcrete. Oftenconsidered "super-accelerators," these are commonly usedwith dry-mix shotcrete. With the increasing use of silicafume, the use of accelerators may decline somewhat. Inthe past, these accelerators were exclusively powderedmaterials added to dry-mix shotcrete materials. Now

both powdered and liquid admixtures are used in bothdry-mix and wet-mix shotcrete. The use of theseaccelerators with a wet-mix process requires that theaccelerator be added at the nozzle rather than batchedwith the other materials.

b. Applications include tunnel support and linings,seawalls, portions of dams, roof construction, slopeprotection, and water-retention structures such as canals,thick concrete sections applied vertically or overhead,rapid repairs, and leaks sealed with flashset shotcrete.Accelerated shotcrete is particularly beneficial in tunnelsupport because it allows rapid section buildup, earlystrength development, and seals water leakage. Forapplications in the splash zone of marine structures, anaccelerating admixture may be used to prevent freshlyplaced shotcrete from being washed away by theincoming tide or by wave action.

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Chapter 3Materials, Proportioning, andProperties

The materials, mixture proportions, and properties ofshotcrete are similar in many respects to conventionalconcrete. Much of the guidance of EM 1110-2-2000 forconventional concrete applies to shotcrete as well.

3-1. Cementitious Materials

a. Portland cement.

(1) Cement requirements for shotcrete are similar tothose for conventional concrete. Portland cement mustmeet the requirements of CRD-C 2011 (American Societyfor Testing and Materials (ASTM) C 150), Type I or II.Where the shotcrete will be exposed to soil or waterhigh in soluble sulfates, Type II or V should be used asdescribed in EM 1110-2-2000. Blended cement mustmeet the requirements of CRD-C 203 (ASTM C 595),Type IP or IS, and moderate sulfate resistance may bespecified by adding the suffix MS to the typedesignation. Where structural requirements require highearly strength, Type III meeting the requirements ofCRD-C 201 (ASTM C 150) cement should beconsidered.

(2) Low-alkali cement must be specified when theaggregates used are regarded as chemically reactive withthe alkalies in the cement (see EM 1110-2-2000).

(3) Air-entraining cement has been used with thewet-mix process and has achieved varied results, with theair content generally much lower than in conventionalconcrete. Generally, the use of air-entraining cement isnot recommended, since in-place air contents are affectedby external factors such as air pressure, hose lengths, andequipment type. AEA’s allow flexibility to compensatefor these factors.

b. Pozzolan. When added to a portland-cementmatrix, pozzolan reacts with the calcium hydroxide andwater to produce more calcium silicate gel.

1All CRD-C designations are toHandbook for Concreteand Cement, 1949, US Army Engineer WaterwaysExperiment Station. Parenthetical references are ASTMequivalents.

Consequently, shotcretes with pozzolan may exhibitimproved long-term strength performance and lowerpermeability. Pozzolan is sometimes added to wet-mixshotcrete to enhance workability, improve pumpability,increase resistance to sulfate attack, and reduce expansioncaused by the alkali-silica reaction. The use of fly ashfacilitates pumping shotcrete long distances. Portlandcement replacement with pozzolan should be carefullyconsidered, since early age strength development isdelayed. Pozzolans should conform to CRD-C 255(ASTM C 618). Natural pozzolans and fly ash are nottypically used with dry-mix shotcrete. However, silicafume is often used in dry-mix shotcrete and does notdelay strength development.

c. Silica fume.

(1) Silica fume is an extremely fine, amorphouspozzolanic material which is a waste product of thesilicon, ferrosilicon, or other silicon alloy production insubmerged-arc electric furnaces. The silica fumecondenses from the exhaust gases forming extremelyminute spherical particles. The material is over85 percent silica dioxide, is approximately 100 timesfiner than portland cement, and has a specific gravityranging from 2.1 to 2.6.

(2) Silica-fume additions create several favorableconditions in shotcrete. Because of the pozzolanic natureof silica fume, its addition results in improved strengthand durability. Because of the its extreme fineness, silicafume particles fill the microscopic voids between cementparticles further reducing permeability and increasing thedensity of the shotcrete. Shotcrete mixtures with silica-fume additions display increased adhesion and cohesion.

(3) Since silica fume is so fine, the material cannotbe effectively handled in its dry, natural form.Consequently, silica fume is commercially available inseveral processed forms. In one form, silica fume isdensified to 30 to 40 pounds per cubic foot (pcf) loosebulk density. Further modifications include the additionof powdered water-reducing admixtures (WRA) toproduce a formulated product. Silica fume is alsoavailable in a pelletized form. Significant mixing actionis necessary to completely break down and dissolve thepellets. Slurried silica fume is produced by mixingnearly equal weights of silica fume and water. Slurriesare also further modified to include water-reducingadmixtures.

(4) Silica-fume additions to wet-mix shotcrete mustbe made in conjunction with the addition of normal and

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high-range WRA’s. Silica-fume additions withoutWRA’s would necessitate large water additions tomaintain a suitable workability level. The additionalwater increases the water-cement ratio and negates thebenefits of the silica-fume addition. On the other hand,WRA’s are not recommended for silica-fume additions todry-mix shotcrete since the total mixture is in contactwith water for only the time when the mixture exits thenozzle and impacts the shooting surface. The use ofWRA’s into dry-mix shotcrete would cause thecompacted shotcrete to slough and sag on the surface asthe admixture takes effect.

(5) For wet-mix shotcrete, any of the packagingprocesses are applicable. If the silica fume is notprepackaged with a WRA, such an admixture must bebatched. Dry-mix shotcrete is best proportioned usingdry processed products of silica fume.

3-2. Aggregate

a. Aggregate should comply with the qualityrequirements of CRD-C 133 (ASTM C 33). Table 3-1shows acceptable grading limits. Grading No. 1 shouldbe used if a mortar mixture is desired. Gradings No. 2and 3 contain coarse aggregate; the latter is similar to aconventional 19.0-mm (3/4-inch) nominal maximum sizeaggregate, except for a reduction in the larger sizes tominimize rebound. Aggregate failing to comply withthese gradings may be used if preconstruction testsdemonstrate that it gives good results. However, auniform grading is essential. Coarse and fine aggregateshould be batched separately to avoid segregation.

b. Fine aggregate for finish or flash coats and certainother special applications may be finer than Grading

No. 1. Finer fine aggregates, however, generally produceshotcretes having greater drying shrinkage, while coarsersands result in more rebound.

c. Lightweight-aggregate shotcrete is most practicalfor the dry-mix process. Since moisture and aggregatecontact is initiated at the nozzle, the severe workabilityreductions common in conventional lightweight concreteproduction do not occur.

3-3. Water

a. Mixing water. Potable water should be used. Ifthis is not available, the proposed water source should betested according to CRD-C 400.

b. Curing water. No special requirements arenecessary for curing water applied to shotcrete (ASTM1978). Water for curing of architectural shotcreteshould be free from elements that will cause staining.

3-4. Chemical Admixtures

a. Use of admixtures.Because of shotcreteequipment limitations, the use of admixtures in shotcreteis not the same as in conventional concrete. Admixturesshould be tested in the field prior to use on large jobs toensure that the desired properties are achieved. Chemicaladmixtures used in shotcrete should comply with theappropriate requirements given in CRD-C 625 (ASTMC 1141). ACI 212.3R (paragraph A-1, ACI (1991a)),"Chemical Admixtures for Concrete," contains detailedinformation on general use in concrete.

b. Air-entraining admixture (AEA).The use ofAEA’s in shotcrete is practical only in wet-mix shotcrete.

Table 3-1Grading Limits for Aggregate

Percent by Mass Passing Individual Sieves

Sieve Size Grading No. 1 Grading No. 2 Grading No. 3

3/4-inch 1001/2-inch 100 80-953/8-inch 100 90-100 70-900.19 inch (No. 4) 95-100 70-85 50-700.093 inch (No. 8) 80-100 50-70 35-550.046 inch (No. 16) 50-85 35-55 20-400.024 inch (No. 30) 25-60 20-35 10-300.012 inch (No. 50) 10-30 8-20 5-170.006 inch (No. 100) 2-10 2-10 2-10

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Due to the loss of air during the gunning process of thewet-mix shotcrete, the AEA should be batched so that themeasured air contents in the plastic mix prior to pumpingare twice the desired hardened shotcrete air content. Themixing process required to form the air bubbles does notoccur in the dry-mix process, hence a suitable air-voidsystem is not generated using the admixture. Airentrainment has slightly reduced rebound.

c. Water-reducing and retarding admixtures.WRA’s meeting the requirements of CRD-C 87 (ASTMC 494) are readily adapted to the wet-mix process but arenot used in dry-mix shotcrete due to the ineffectivenessof the admixture when adding the admixture and water atthe nozzle. Retarding admixtures are seldom used inshotcrete, except for near horizontal surfaces wheresubsequent finishing of the shotcrete surface is required.

d. Accelerators.

(1) Accelerators are essential in some shotcreteapplications, such as tunnel support, where rapid sectionbuildup and rapid strength development are necessary.Early accelerators were powders consisting of solublealuminates, carbonates, and silicates. Modernaccelerators, both powdered and liquid, fall into a wideassortment of chemical makeups. Accelerators havedifferent effects depending on their chemistry, thechemistry of the cement, and the dosage rate of theadmixture. Some of the commercial accelerators containcalcium chloride. Many are caustic, particularly thepowdered materials, although not as caustic as in thepast.

(2) Tests should be made to establish thecompatibility of the particular accelerator with thecement proposed for use on the project and to determinethe amount of such accelerator required. Manyaccelerators reduce 28-day strengths by 25 to 40 percent,depending upon the compatibility of the accelerator andcement. Where the aggregate is reactive, the alkalicontent of the admixture added to that of the cementshould not exceed 0.6 percent by mass of the cement.

(3) Accelerators may reduce the frost resistance ofthe shotcrete. Some may be very caustic and thereforeare a safety hazard. For these reasons and because oftheir cost, accelerators should only be used wherenecessary and then only in the minimum quantitynecessary to achieve the desired results.

(4) Calcium chloride, an accelerator, should never beused in an amount greater than 2 percent by mass of the

cement, except where "flash set" is needed for stoppageof leaks. It should not be used in sulfate exposures, norwhere the shotcrete encases dissimilar metals (such asaluminum and steel) in contact with each other. Noadmixtures containing calcium chloride should be usedwhere the shotcrete is in contact with prestressing steel.

(5) Liquid accelerators are generally added at thenozzle for dry-mix or wet-mix shotcrete. Powderedaccelerators are generally used only for dry-mixshotcrete, added as a powder to the dry ingredients.Accelerators used in wet-mix shotcrete produce quickstiffening, then initial set. However, the final set usuallyoccurs much later than for dry-mix shotcrete. The timeof set can be varied widely with these materials,including initial set in less than 1 minute, and final set inless than 4 minutes. Some of these materials can also beused to create a "flash set" for special applications.

e. Polymers.The addition of certain latex emulsionsto a conventional portland-cement shotcrete has increasedboth tensile and flexural strength, improved bonding, anddecreased permeability. One common use of thesematerials has been in the repair of concrete structures inmarine environments and those subject to chemicalattack. A latex with favorable properties should beselected and the field personnel must be instructed in itsbehavior.

f. Bonding compounds.Bonding compounds aregenerally not recommended in shotcrete work, becausethe bond between shotcrete and properly preparedsubstrates is normally excellent. When improperly used,bonding compounds can act as bond breakers. Bondingagents should not be used in shotcrete work without aninvestigation into their effectiveness in each case.

3-5. Reinforcing Steel

a. Reinforcing bars for shotcrete should meet thesame specifications as for conventional concrete. Becauseof the placement method, the use of bars larger thanNo. 5 or heavy concentrations of steel are not practical.Large bars make it difficult to achieve adequate build-upof good quality shotcrete behind the bar and heavyconcentrations of steel interfere with the placement ofshotcrete. In general, bar spacings of 6 to 12 inches arerecommended for shotcrete reinforcement.

b. It is often advantageous to specify as welded wirefabric, reinforcement either uncoated, galvanized, orepoxy coated. Flat stock should usually be specified inlieu of rolled fabric. Because of the rolled configuration,

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rolled welded wire fabric is difficult to place at specifiedlocations. Wire spacing should be as wide as possible toallow shotcrete to be built up behind. Spacing of6 inches is recommended, however wire spacing as lowas 2 inches has been used with 4 inches being moretypical.

c. In repair work, a thin shotcrete coating may notrequire reinforcement. When reinforcement is exposedin the old concrete, but not severely corroded, it may bethe only reinforcement necessary. In other cases,additional reinforcement (bars or wire mesh) may berequired to replace corroded steel to control temperaturecracking, if not to satisfy structural considerations.

3-6. Fiber Reinforcement

a. Steel fiber reinforcement.Steel fibers have beenused in shotcrete to increase its ductility, toughness,impact resistance, and reduce crack propagation. Thefibers are commercially available in lengths ranging from1/2 to 3 inches. Typical fiber lengths for shotcrete rangefrom 3/4 to 1-1/2 inches and are used in the amount of1 to 2 percent by volume of the shotcrete. The fibershave little effect on compressive strength and produceonly modest increases in flexural strength. However,they provide continued and, at times, improved loadcarrying capacity after the member has cracked.

b. Steel fiber source.Steel fibers are manufacturedin several ways. Wire fibers are produced from drawnwire that has been subsequently cut or chopped. Flatsteel fibers are cut or slit from sheet of steel or byflattening wire. The melt-extraction process is used to"cast" fibers by extracting fibers from a pool of moltensteel. Consequently, fibers are round, flat, or irregular inshape. Additional anchorage is provided by deformationsalong the fiber length or at the ends. Deformations canbe natural irregularities, crimps, corrugations, hooks,bulbs, and others. Collated fibers and fibers withnoncircular cross sections reduce the handling andbatching problems common with straight, round fibers.

c. Polypropylene-fiber reinforcement.Collatedfibrillated-polypropylene (CFP) fibers are used inshotcrete. Fiber lengths of 1/2 to 2-1/2 inches have beenthe most common in use. The common application hasbeen 1 to 2 pounds of polypropylene fibers per cubicyard of shotcrete. The primary benefit is to controlthermal and drying shrinkage cracking. More recently,polypropylene doses of up to 10 pounds per cubic yardhave been used successfully yielding shotcrete toughnessperformance approaching that of some steel fiber

shotcrete (Morgan et al. 1989). The hazard fromrebound is much less when polypropylene is used. Themost common specified length for polypropylene is1-1/2 inches, although longer lengths are no problem.

d. Glass fiber source. Glass fibers are made fromhigh zirconia alkali-resistant glass designated AR glass.Glass fibers, used for fiberglass reinforcement, aredesignated E glass and should not be used in a portland-cement matrix. While glass fibers may be as small as0.0002 inch, they are usually bonded together intoelements having a diameter of 0.0005 to 0.05 inch.Glass fiber lengths are typically 1 to 2 inches, but a widerange of lengths is possible.

e. Applicable technology. ACI 506.1R, "State-of-the-Art Report on Fiber Reinforced Shotcrete" (ACI1991e), is a comprehensive document covering the fullrange of fiber shotcrete technology.

3-7. Proportioning of Shotcrete

a. Considerations.In general, conventional concretetechnology may be applied to shotcrete proportioning.Prior to mixture proportioning, the following should beconsidered:

(1) Type of dry-mix or wet-mix shotcreteappropriate for the work.

(2) The specific job constraints on the shotcretework.

(3) The type of specification.

(a) Performance versus prescription.

(b) Contractor versus Government mixtureproportioning.

A mixture proportioning sample submitted is presented inAppendix D.

b. Mixture proportioning trial batching.

(1) Since shotcrete performance is highly dependenton application procedures, trial batching and testing is acritical operation in verifying mixture performance. Thebatching and mixing of wet-mix shotcrete is practicallyidentical to conventional concrete; only the fabrication ofspecimens is different. However, dry-mix is a distinctprocess. It is normal procedure to obtain trial mixtureproportions for shotcrete from the contractor. Along with

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the proportions, test panels and cores of the shotcrete arehighly recommended, as discussed in Chapter 5.

(2) Test panels are particularly important for dry-mixshotcrete because laboratory mixtures cannot duplicateas-shot dry-mix shotcrete. Typically, a performancespecification of 12-hour, 7-day and/or 28-daycompressive strengths will be specified, along with agrading for the aggregate. Both the wet- and dry-mixmethods will yield a higher as-shot cement content andlower coarse aggregate content, due to rebound of theaggregate.

c. Chlorides. The total chloride ion (Cl-) from allsources including mixing water, cement, admixture, andaggregate should not exceed 0.06 percent by mass ofcement for prestressed members. For other reinforcedshotcrete applications, this limit is increased to0.10 percent in a moist environment exposed to chlorideand 0.15 percent in a moist environment not exposed tochloride.

d. Nominal maximum size aggregate (NMSA).Theselection of NMSA depends on several factors. Themajor factors are the allowable shrinkage performance,size of the placement, and the rigidity of the substrate.The amount of rebound, inherent in the shotcrete process,depends on the ability of the substrate and the placedshotcrete to cushion subsequently placed shotcrete.Shotcrete for thin linings on rock or concrete experienceshigh rebound. Thicker sections and sections on soilstructures experience lower rebound. For placements ofthin layers on hard surfaces, coarse aggregate should beminimized or eliminated in the mixture to minimizerebound.

e. Wet-mix proportioning.Mixture proportioningprocedures for the formulation of conventional concretefor pumping applications are applicable for wet-mixshotcrete. The nominal maximum aggregate size isusually 3/4 inch or smaller. The batched cement contentwill typically range from 500 to 700 pounds per cubicyard. Rich mixtures are common for shotcrete,especially if vertical or overhead shotcrete placement isrequired. The limiting factor for cement content in amixture is often governed by the amount of cementnecessary for the shotcrete to adhere to a wall or ceiling,not the specified compressive strength. It is not unusualfor shotcrete used in vertical and overhead placement tohave 28-day strengths in excess of 4,500 psi, due only tothe amount of cement necessary to make the shotcreteadhere.

(1) Workability. The slump for wet-mix shotcreteshould be near the minimum that the pump will handle.A 3-inch slump should normally be considered themaximum slump to be used. Excess slump will yieldlower-strength shotcrete which will tend to slough off ofvertical and overhead surfaces.

(2) Entrained air. If air entrainment is to be used,an air content ranging from 8 to 12 percent prior topumping is typical. The in-place shotcrete will haveabout one-half of the entrained air that was recorded atthe pump.

(3) Admixtures. Additional admixtures generallybehave the same in wet-mix shotcrete as they do inconventional concrete. Any admixture should be testedin the mixture proportioning studies and on the testpanels prior to usage.

f. Dry-mix proportioning. There is no establishedmethod of proportioning dry-mix shotcrete. Since it isnot practical to perform laboratory trial mixtures fordry-mix shotcrete, field testing of dry-mix proportions ishighly advisable, especially if no field data exist for agiven dry-mix. The in-place aggregate grading will befiner than the batched grading due to rebound, especiallyif larger aggregate sizes are used. As with wet-mixshotcrete, the in-place cement factor will be higher also.

(1) Compressive strength. ACI 506 (paragraph A-1,ACI (1991d)), reports typical data on strength versuscement content of dry-mix shotcrete as shown inTable 3-2.

Table 3-2Strength Versus Cement Content, Dry-Mix Shotcrete,Typical Data

28-day Compressive Strength Cement Contentpsi lb

3,000 500-6504,000 550-7005,000 650-850

(2) Workability. The workability of the shotcrete iscontrolled by the nozzleman at the placement. Wateradjustments may be made instantaneously at theplacement by adjustment of the water valve.

(3) Entrained air. Air-entraining admixtures havelittle effect on dry-mix shotcrete since there is no mixingof admixture water and aggregate until impact on the

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shooting surface. Some contractors prefer to add an air-entraining admixture to a mix to improve workability.

(4) Admixtures. Accelerators are typically the onlyadmixtures that are used in dry-mix shotcrete. Theseshould be tested to determine that they are compatiblewith the cement being used and produce the requiredaccelerated times of setting.

(5) Cement content. Cement contents are similar tothose used in wet-mix shotcrete. Batch weights forcement of 500 to 700 pounds per cubic yard are typical,with 28-day compressive strengths of more than4,500 psi common for the mixtures used for vertical andoverhead placement.

(6) Water-cement ratio. The batched water-cementratio for coarse aggregate dry-mix shotcrete typicallyvaries between 0.30 to 0.40.

g. Fiber-shotcrete proportioning.

(1) Steel fiber lengths for shotcrete are typically1 inch but often range from 3/4 inch to 1-1/2 inches.The fiber should be at least 1/4 inch longer than thediameter of the maximum aggregate size. Shorter fibersare more easily pumped through the system, althoughmore are required for equivalent performance. Fiberbatch quantities are dependent on required shotcreteproperties. Typical fiber proportions range from 0.5 to2.0 percent by volume of shotcrete. Deformed fibersand fibers with end anchorage provisions produceshotcrete with properties equivalent to straight fibers atmuch lower fiber loadings. Since fibers tend to reboundat a greater rate than does aggregate, the fiber batchquantity should be adjusted accordingly.

(2) Proportioning mixtures using glass fibers isdiscussed by the PCI (1981). Proportioning mixturesusing polypropylene fibers is discussed by Morganet al. (1989).

h. Silica-fume shotcrete proportioning.Silica fumeis added to a shotcrete mixture as a cement replacementor in addition to cement. Batch quantities range from7 to 15 percent by mass of cement. Strengthenhancement and decreased permeability is apparent atthe lower dosages. Reductions in rebound and increasesin cohesiveness for thick applications do not occur untilsilica-fume dosages exceed approximately 14 percent.Further mixture adjustments to wet-mix shotcrete may benecessary to attain the required workability level.

i. Polymer-modified shotcrete. Polymer emulsionsare typically 50 percent solids and 50 percent water. Theliquid portion of the emulsion replaces the equivalentvolume of water, and the solid portion replaces the samevolume of combined solids. Additional adjustments toattain desired workability levels may be required.

3-8. Properties of Shotcrete

As is the case with conventional concrete, shotcreteproperties vary dramatically depending on water-cementratio, aggregate quality, size, and type, admixtures used,type of cement used, and construction practices. Theproper use of admixtures, fibers, silica fume, andpolymers can improve certain properties. Depending onthe needs of the particular application, properties of theshotcrete materials and mixtures should be tested prior tofinal application.

a. Strength. In terms of compressive and flexuralstrength, shotcrete can produce strength generallyequivalent to conventional concrete. Compressivestrengths of up to 12,000 psi have been reported fromdrilled cores from test panels, and 10,000 psi is oftenquoted in the literature as a typical high strength. Thepracticality of strengths over 5,000 psi should beestablished by laboratory or field testing prior to finaluse. The ratio between compressive and flexural strengthappears to be the same as for conventional concrete.Relationships between water-cement ratio and strengthalso appear to follow normal patterns, with higherstrength associated with lower water-cement ratios. Earlystrength of shotcrete can be very high, reaching 1,000 psiin 5 hours and 3,000 psi in 24 hours.

b. Bond strength. Although few data on bondstrength appear to exist, bond strength with othermaterials is reported to be generally higher than can beachieved with conventional concrete. ACI 506R(paragraph A-1, ACI (1991d)) and Mahar, Parker, andWuellner (1975) provide some data on bond strengths ofshotcrete to various substrates.

c. Shrinkage. Drying shrinkage is most influencedby the water content of the mixture. Typical values ofunrestrained shrinkage range from 600 to1,000 millionths. Shrinkage is reduced in coarse-aggregate shotcrete and increased in shotcrete withoutcoarse aggregate or shotcrete subject to high rebound.Shotcrete containing silica fume has a tendency to exhibitmore shrinkage before setting than shotcrete withoutsilica fume. Procedures similar to those outlined by

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Holland (1987) to prevent plastic shrinkage crackingshould be implemented.

d. Resistance to freezing and thawing.Wet-mixshotcrete frost resistance is ensured by entraining aproper air-void system. Typically, an air content of 8 to12 percent in the mixture results in in-place shotcretehaving a proper air-void system. Although manydry-mix applications have performed well when subjectedto mild freezing and thawing, dry-mix shotcrete is moresubject to problems from freezing and thawing thanwet-mix shotcrete. This is due to the difficulty inentraining air and creating an adequate air-void system indry-mix shotcrete.

e. Density and permeabilityof shotcrete can beexcellent, provided good practices are followed in thefield.

f. Toughness. The addition of fibers to shotcretecan result in a product displaying significant loadcarrying capability after the occurrence of the first crack.The relationship of post-crack load capacity to loadcapacity at first crack is defined as toughness. The type,size, shape, and amount of fiber determines the extent ofthis performance. The use of the toughness index byload-deflection testing, CRD-C 65 (ASTM C 1018),provides a rational means of specifying and comparingperformance. However, recent concerns have developedover the specifics of applying this testing procedure(Gopalaratnam et al. 1991). The reader is advised toconsider the cited references and contact CECW-EG forfurther guidance.

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Chapter 4Equipment and Crew

4-1. General Equipment

There are two basic types of shotcrete deliveryequipment known as guns: dry-mix guns and wet-mixguns. Although either type may be used for mostshotcrete work, each has its limitations. It is importantto select equipment which is capable of placing the jobmixture and maintaining an adequate production rate.

4-2. Dry-Mix Process

Cement and damp aggregate are thoroughly mixed, orpremixed, and prebagged cement and aggregate are fedthrough a premoisturizer. The cement-aggregate mixtureis then fed into the gun. The mixture is introduced intothe delivery hose via a metering device such as a feedwheel. Compressed air is added at the gun and themixture is carried through the delivery hose to thenozzle. The nozzle is fitted inside with a perforatedwater ring through which water and admixtures areintroduced under pressure and intimately mixed with theother ingredients as they go through the nozzle. Theconcrete is propelled from the nozzle at high velocityonto the receiving surface.

a. Description of guns. Dry-mix guns are dividedinto two classifications, the double chamber gun and thecontinuous feed gun, each of which is capable ofdelivering mixtures in a wide range of consistencies.

(1) Double chamber. The first gun developed wasthe double chamber or pot type, introduced in the early1900’s, shown in Figure 4-1. Although the materialenters the upper chamber in batches, the valvearrangement is such that the discharge from the lowerchamber is continuous. Until recent years, this gun hadbeen used only for mortar mixtures and the productionrate was low, but larger, high-production units which willhandle coarse aggregate up to about 3/4 inch are nowavailable.

(2) Continuous feed. The continuous-feed gun wasintroduced about 1960 and is shown in Figure 4-2. Mostof these guns will handle mortar or concrete mixtureswith aggregate up to about 3/4-inch and will produceshotcrete at production rates up to 2 cubic yards perhour.

b. Plant layout. A typical plant layout for a dry-mixshotcreting operation, including air and water supplies,gun, delivery hose, and nozzle, is shown in Figure 4-3.

4-3. Wet-Mix Process

Cement, aggregates, and admixtures (except accelerators)are thoroughly mixed. The mixture is fed into the gunand propelled through the delivery hose to the nozzle bycompressed air or pneumatic or mechanical pumping.Air is injected at the nozzle to disperse the stream ofconcrete and generate the velocity for shotcreteplacement.

a. Description of guns.

(1) Pneumatic-feed. In the pneumatic-feedequipment shown in Figure 4-4, the premixed mortar orconcrete is conveyed from the gun through the deliveryhose to the nozzle by slugs of compressed air. At thenozzle additional air may be added if needed to increasethe velocity and improve the gunning pattern. Thisequipment can handle mixtures of a consistency suitablefor general shotcrete construction, using mixturescontaining up to 3/4-inch aggregate. Guns with a dualmixing chamber and a two-way valve allow mixing ofmaterials and a continuous flow operation.

(2) Positive displacement. In the positivedisplacement equipment shown in Figure 4-5, theconcrete is pumped or otherwise forced through thedelivery hose without the use of compressed air. Air isinjected at the nozzle to disperse the stream of concreteand impart the velocity necessary for shotcreteplacement. Positive displacement delivery equipmentrequires a wetter mixture than pneumatic-feed equipment,and the velocity of the shotcrete being applied is lower.It is difficult to apply shotcrete to vertical and overheadsurfaces by this method unless a suitable accelerator isused. This equipment can also satisfactorily shootmaterial containing 3/4-inch aggregate.

b. Plant layout. A typical plant layout for each ofthe wet-mix processes is given in Figures 4-6 and 4-7.

4-4. Auxiliary Equipment

a. Batching and mixing equipment.Most shotcreteis batched and mixed in the field using portable mixingequipment or delivered in mixer trucks from a localready-mixed concrete plant. Mixing equipment for

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Figure 4-1. Cross section of typical double-chamber dry-mix gun (Crom 1966; copyrightpermission granted by ACI)

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Figure 4-2. Cross section of typical continuous-feed dry-mix gun (Mahar, Parker, and Wuellner 1975)

Figure 4-3. Typical plant layout for dry-mix shotcreting (Crom 1966; copyrightpermission granted by ACI)

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Figure 4-4. Cross section of pneumatic-feed shotcrete gun (Hoffmeyer 1966;copyright permission granted by ACI)

Figure 4-5. Schematic of positive displacement pump (Fredricks, Saunders, and Broadfoot1966; copyright permission granted by ACI)

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Figure 4-6. Typical plant layout for wet-mix pneumatic-feed equipment

Figure 4-7. Typical plant layout for wet-mix positive displacement equipment

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shotcrete is of the batch or the continuous type. Whereready-mixed concrete is used, it should conform toCRD-C 31 (ASTM C 94). Equipment for the batch typeshould conform to CRD-C 31 (ASTM C 94). In thecontinuous type, individual ingredients are fed to a mixerscrew by means of variable speed augers, belt-feedsystems, or a combination of both. This equipmentshould conform with CRD-C 98 (ASTM C 685). Ahopper is sometimes used in high production units ofboth these types to collect and feed the mixture asrequired. Water-metering systems are also available toredampen the mixture. Batching and mixing equipmentmust be capable of maintaining an adequate andcontinuous flow of homogeneous material. Batching bymass is preferred and will normally be required. Watermay be batched by mass or volume. For small jobs,approval may be given to batching by a volumetriccontainer, provided periodic weight checks are made.Since many shotcrete jobs have a low production rateand are in isolated locations, mixing is often done by asmall drum mixer at the jobsite.

b. Admixture dispensers.Admixtures may be addedwhen needed during mixing or at the nozzle, dependingon their properties and the type of shotcrete process (dryor wet).

(1) In the dry-mix process, dry (powder) admixturesare usually introduced into the mixture during batching.If a continuous feed gun is being used, they may also beadded directly into the gun hopper by a special dispenser,usually an auger-type dry dispenser driven by andcalibrated to the gear train of the shotcrete machine. Thedispenser should be capable of metering a precisequantity of admixture, usually 1 to 4 percent by mass ofthe cement, into the mixture, and must be capable ofaccurately varying the ratio of accelerator to cement.

(2) In the dry-mix process, liquid admixtures mustbe introduced at the nozzle through the mixing water.The admixture may be premixed with water and pumpedto the nozzle or added directly to the mixing water at thenozzle.

(3) In the wet-mix process, dry or liquid admixturesmay be added to the mixture when batching provided thepumping properties are not adversely altered. As anexample, an accelerator would create problems if addedduring batching, while a high-range water reducingadmixture (HRWR) might have beneficial effects. Inwet-mix applications, only liquid admixtures may beadded to the air supply at the nozzle. They are

proportioned to the delivery rate of the mixture throughthe material hose.

c. Air compressor. A properly operating aircompressor of ample capacity is essential to asatisfactory shotcreting operation. The compressorshould maintain a supply of clean, dry, oil-free airadequate for maintaining sufficient nozzle velocity for allparts of the work while simultaneously operating allair-driven equipment and a blowpipe for cleaning awayrebound.

(1) Table 4-1 gives recommendations for compressorcapacity, diameter of delivery hose, and maximumproduction rate for the dry-mix process. The operatingair pressure is the pressure driving the material from thedelivery equipment into the hose and is measured by agage near the material outlet of the gun. The air pressureshould be steady (nonpulsating). A compressor ofadequate capacity will ensure that the operating airpressure is sufficient.

(2) The values shown in Table 4-1 are based on ahose length of 150 feet, with the nozzle not more than25 feet above the delivery equipment. Operatingpressures should generally not be less than 40 psi, when100 feet or less of shotcrete hose is used. Operatingpressures are generally increased about 5 psi for eachadditional 50 feet of hose and about 5 psi for each25 feet that the nozzle is raised above the gun.

(3) Air requirements for the wet-mix process havenot been thoroughly studied. In general, however, thevalues for the pneumatic-feed type are a little lower thanthose shown, but back pressures are higher. Positivedisplacement equipment requires at least 105 ft3/min. at100 psi at the air ring for proper operation.

(4) Certain moisture conditions will cause anincrease of water vapor in the compressed air streamwhich will adversely affect the shotcrete operation. Amoisture trap or filter should always be installed in thesupply line from the compressor.

d. Water supply for dry-mix equipment.Watersupply booster pumps should be capable of supplying atleast a 10-gallon/minute flow at 60 psi at the nozzle forstandard nozzles. The water pressure must be constantand must be 15 to 30 psi or more greater than theoperating air pressure.

e. Aggregate premoisturizer.It is common practicein large volume dry-mix shotcrete projects to prebag all

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the shotcrete materials together in a dry condition at thesite. It is advantageous to premoisturize this material to3-6 percent, by dry mass, prior to entering the shotcretegun. A premoisturizer is a piece of equipment stagedjust before the shotcrete gun that uniformly distributesand mixes water to a continuous feed of dry materials.

4-5. Special Equipment

a. Steel fiber-reinforced shotcrete.It is critical thatfibers be uniformly distributed throughout the mixture.Proper batching procedures and equipment can preventthe possible problems of fibers tangling together intofiber balls. For small projects, no special equipment isnecessary. Fibers can be manually added to the mixtureat an appropriate rate to prevent balling of fibers. Largerdry-mix shotcrete projects use prebagged material,including predistributed fibers. Specialized fiber feederequipment, consisting of a drum and screen mechanismthat uniformly screens the individual fibers into theshotcrete mixture, is available for continuous productionof shotcrete. As with other continuous-feed systems,calibration of the system is mandatory to achieve properproportions.

b. Silica-fume shotcrete.No special equipment isnecessary for batching and mixing silica-fume shotcrete.Densified or slurried packaging eases manual batchingmethods common for low production-rate projects.Higher production-rate projects use bin systems similar toflash-feed systems, liquid pumping systems similar toliquid admixture systems, or prebagged materials.

c. Nozzles.A dry-mix nozzle typically consists of atip, water ring, control valve, and nozzle body arrangedin a wide variety of nozzle tips, nozzle sizes, andconfigurations. Figure 4-8 shows a section of a dry-mix

nozzle. A wet-mix nozzle usually consists of a rubbernozzle tip, an air injection ring, a control valve, andnozzle body. Figure 4-9 shows an example of a wet-mixnozzle section. Some investigations have shownimproved mixing action and less rebound for dry-mixshotcrete when a special prewetting nozzle is used andthe water ring is placed in the hose 1 to 8 feet before ofthe nozzle. This has been particularly effective for silica-fume shotcrete.

d. Remote-controlled nozzles.During recent years,the use of remote-controlled nozzles has becomeincreasingly popular, particularly for underground work.These machines are truck-mounted and include aboom-mounted nozzle, a gun, and an air compressor.The remote controls allow the nozzleman to rotate thenozzle in an 18-inch-diameter circle to allow properapplication technique. The nozzleman can also swing thenozzle around 360 degrees and maneuver it closer to orfarther from the surface being shot. Significant economyis realized because of higher placement rates and reducedcrew size. Because of the remote location of theoperator, some safety benefits can be realized fromavoiding rebound of aggregates and fibers.

4-6. Crew Composition

a. The quality of shotcrete depends largely on theskill of the application crew. The shotcrete crew mayconsist of four to eight individuals, depending on the sizeof the operation and the type and setup of equipment. Atypical crew may include the foreman, nozzleman,delivery equipment operator, and nozzleman’s helpers.Additional personnel such as a delivery equipmentoperator helper and operator for haulage of materials mayalso be necessary. By far, the most important member ofthe crew is the nozzleman.

Table 4-1Compressed Air Required for Dry-Mix Guns

Compressor Capacityat 100 psift3/min

Inside Diameter ofDelivery Hoseinches

Maximum ProductionRateyd3/hr

365 1 4

425 1-1/4 6

500 1-1/2 9

700 1-3/4 10

900 2 12

1,000 2-1/2 15

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Figure 4-8. Typical dry-mix nozzle (paragraph A-2, ACI 1991c; copyright permission granted by ACI)

Figure 4-9. Typical wet-mix nozzle (paragraph A-2, ACI 1991c; copyright permission granted by ACI)

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b. The success of the shotcrete crew depends largelyon the ability of the nozzleman since he controls thesurface preparation, the material delivery rate, theimpingement of the shotcrete particles on the surface, thethickness, and, in the dry-mix process, the water-cementratio. The nozzleman should have served anapprenticeship on similar applications and should becertified, as discussed in Chapter 5, for his ability tosatisfactorily perform his duties and to gun shotcrete ofthe required quality. During production he will performthe following duties:

(1) Ensure that all surfaces to be shot are clean andfree of laitance or loose material, using air andair-and-water blast from the nozzle as required.

(2) Ensure that the operating air pressure is uniformand provides proper nozzle velocity for good compaction.

(3) Regulate the water content so that the mixturewill be plastic enough to give good compaction and alow percentage of rebound, but stiff enough not to sag.(In the dry-mix process the nozzleman actually controlsthe mixing water, while in the wet-mix process he directschanges in consistency as required.)

(4) Hold the nozzle at the proper distance and asnearly normal to the surface as the type of work willpermit to secure maximum compaction with minimumrebound.

(5) Follow a sequence that will fill corners withsound shotcrete and encase reinforcement without voids

behind the steel, using the maximum practicable layerthickness.

(6) Determine necessary operating procedures forplacement in close quarters, at extended distances, oraround unusual obstructions where placement velocitiesand mixture consistency must be adjusted.

(7) Direct the crew to start and stop the flow ofmaterial and stop the work when material is not arrivinguniformly at the nozzle.

(8) Ensure that sand lenses, slough pockets, orlaminations are cut out for replacement.

(9) Bring the shotcrete to finished lines in a neatand workmanlike manner.

(10) Assume responsibility for safety in the areawhere shotcrete is applied. He must be aware of otherpeople in his immediate vicinity and take care not todirect the shotcrete stream irresponsibly. He shouldalways maintain a firm grip on the nozzle and plan hismovements so that he does not lose control of thematerial hose.

c. The nozzleman’s apprentice or helper operates anair blowpipe at least 3/4 inch in diameter to assist thenozzleman in keeping all rebound and other loose orporous material out of the new construction (except inclasses of work where the trapped rebound can readily beremoved by the nozzleman). He also assists thenozzleman in moving hoses and in other assignments asrequired.

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Chapter 5Preconstruction Testing and Evaluation

5-1. General

Regardless of the size of the project, some form ofpreconstruction testing and evaluation must be done toassure that competent personnel, equipment, andmaterials are provided. Prior to application of shotcrete,the quality assurance team must assess the suitability ofthe shotcrete nozzleman, the materials and mixtureproportions, the equipment, crew, and applicationprocess. These are confirmed by submittal orperformance of:

a. Nozzleman Certification.

b. Mixture Proportioning Testing and/or Data.

c. Preconstruction Demonstration and Testing.

5-2. Nozzleman Certification

a. The success of any shotcrete application isdependent, in large part, on the skills and abilities of thenozzleman. It is imperative that only qualifiedindividuals perform this work. Unlike some other workprocesses, the application of shotcrete cannot tolerateinexperience or marginal workmanship.

b. The ACI has an ongoing Nozzleman CertificationProgram. Specifications should require that allnozzlemen hold such certification. Certification requiresthe successful completion of a two-part writtenexamination on general shotcrete knowledge and specificapplication knowledge. A shotcrete demonstration, theconstruction of test panels which are subsequentlyevaluated for strength, uniformity, and other applicableproperties, is also required.

c. Final approval of ACI certified nozzlemen mustbe contingent on successful demonstration of abilities byapplying shotcrete to preconstruction test panels.

5-3. Mixture Proportioning Evaluation

Unlike the evaluation of conventional concrete mixtures,shotcrete testing is difficult to perform in a laboratoryenvironment. The equipment and technique are integralfactors in the performance of the mixture. The mixtureproportioning study should therefore be conducted under

field conditions insofar as practicable. Mixtureproportions are submitted in one of two ways, trialbatching or historical data submission.

a. Trial batching. Mixture proportions or materials,which have had no previous use, are accompanied bydata verifying material properties, mixture proportions,field conditions, test data, and performance. This work isperformed specifically for the project on which it will beused. This process requires significant lead time, oftenin excess of 45 days, to attain the required 28-daystrength results. More extensive testing will add moretime to this process. This is not a laboratory exercise buta full-scale production of test panels with actualequipment, personnel, and materials. Test panels shouldbe fabricated as described in paragraph 5-4:Preconstruction Demonstration and Testing.

b. Historical data. Often, materials and mixtureproportions that will meet the requirements for thecurrent project are available from use on previousprojects. If past documentation and performance isacceptable, no further testing is necessary. Submissionof the historical mixture proportions will suffice. Thisprocess greatly reduces the lead time required of thecontractor. A historical data submittal includes allmaterial data, mixture proportions, field conditions, andtest reports or data summaries.

5-4. Preconstruction Demonstration and Testing

a. Acceptable equipment and personnel.Prior toplacement of any shotcrete for payment, the contractorshould demonstrate the acceptable performance ofequipment and personnel. This is done by the fabricationof a series of test panels for each nozzleman. These testpanels may also serve for approval of the materials andmixture proportions.

b. Test panels.Fabrication of test panels mounted ina framework is the typical way to evaluate the shotcreteprocess (Figures 5-1 and 5-2). A separate panel shouldbe fabricated for each nozzleman, for each shootingposition to be encountered in the structure; e.g., slab,vertical, or overhead. Where the field shotcrete willcontain reinforcement, this should be duplicated in atleast part of the panels to show whether sound shotcreteis obtained behind reinforcing bars or wire fabric. Eachpanel should be large enough to obtain all the testspecimens needed and also large enough to indicate whatquality and uniformity may be expected in the structure:not less than 30 inches square for mortar mixtures and

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not less than 36 inches square for concrete mixtures.The thickness should equal that of the structure butshould measure no less than 3 inches.

c. Specimen testing.

(1) At least five cubes or cores (Figure 5-3) shouldbe extracted from the interior (at least 4 inches from theedge) of each panel for testing. Cores should have aminimum diameter of 3 inches and a length-to-diameterratio (L/D) of at least one, if possible. Core strengthsshould be corrected for L/D as described in CRD-C 27(ASTM C 42). Cube strengths may be reported asdetermined, or converted to cylinder (L/D = 2) strengthsby multiplying by the factor 0.85.

(2) Panels should be cored or sawn no sooner thanafter 7 days of standard curing. The specimens shouldbe tested in compression at 28 days to evaluate themixture performance. It is not necessary to test at such alate age to evaluate the process. Depending on theexpected strengths, testing at 7 or 14 days is adequate todetermine the suitability of the nozzlemen and process.

(3) Beams for toughness evaluation and flexuralstrength testing can be sawn from the test panels.Typical beam dimensions are 4 by 4 by 16 inches.

Beams must be sawn from the interior of the panel andnot closer than 4 inches from any edge. Beams must betested in the same orientation as shotcrete on thestructure. For example, shotcrete for thin linings resultsin a fiber orientation parallel to the finished surface.Beams sawn from test panels should be tested with theshot surface normal to the load application.

d. Visual examination.Visual examination of sawnsurfaces is the best method of determining the uniformityof the shotcrete. Panels should be sawn into quadrantsafter 7 days of standard curing. The cut surfaces of thespecimens should be carefully examined, and additionalsurfaces should be exposed by sawing the panel whenthis is considered necessary to check the soundness anduniformity of the material. Figure 5-4 shows someproblem conditions that may be encountered. All cut andbroken surfaces should be dense and substantially freefrom laminations and sand pockets.

e. Accelerated testing.Often it is advantageous tocorrelate accelerated strength development of theshotcrete mixtures with the standard laboratory strengthdevelopment. This correlation will allow determinationof mixture performance at ages of 3 to 5 days. Specialequipment and extensive laboratory evaluations arenecessary prior to construction for this testing procedure.

Figure 5-1. Test panel support system (Mahar, Parker, and Wuellner 1975)

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Figure 5-2. Test panel frame system

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Figure 5-3. Cored and quartered test panels

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Figure 5-4. Shotcrete problems obvious from a visual inspection

5-5

- VOIDS OR ·sAND LENSES• CREATED DURING LA YER/NG PROCESS

- DELAMINATED FLASH COAT ON FINISHED SURFACE OF SHOTCRETE

VOIDS BEHIND REINFORCING STEEL

EM 1110-2-200531 Jan 93

f. Load deflection testing.Fiber shotcreteperformance should be specified by use of toughnessindex values as determined by CRD-C 65 (ASTMC 1018). The test procedure should be done using thespecified equipment, preferably a deflection controltesting machine of sufficient stiffness to not bias theresults. Toughness index values, termed I5, I10, and I20,should be selected to be compatible with project serviceconditions. Designers should avoid specifying minimumlimits for the I5 index and instead specify limits for theI10 or I20 indexes.

g. Other tests.Tests for absorption, dryingshrinkage, resistance to freezing and thawing, and otherproperties may also be made if desired, using appropriatespecimens cored or sawed from the panels.

5-5. Alternate Considerations

a. Typically, preconstruction testing and evaluationmust precede the actual work by more than 30 days to

allow time for nozzleman certification at the start andending with strength testing at 28 days. This protractedstart-up period may add significant costs to a small repaircontract and may delay the start of actual construction.

b. In the case where previous acceptable mixtureproportions information is available for the proposedmaterials and proportions, it may be advantageous toeliminate the later-age testing of the shotcrete mixture.Some contracting organizations have found it costeffective to evaluate the nozzleman and equipment at asite convenient to the contractor, often in conjunctionwith the contractor’s ongoing work, to eliminate the earlymobilization and extended standby time of equipment andpersonnel.

c. The designer must always consider the criticalityof the shotcrete placement and the qualifications of thenozzleman when considering whether or not to waivesome of the preconstruction requirements.

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Chapter 6Placement

Shotcreting can be a hazardous operation, especially ifthe work must be conducted in a relatively confined area.The critical hazards include control of the material

(shooting), rebound, plugged nozzle, hose or couplingbreaks, caustic materials, and dusting. All shotcreteoperations must be performed in accordance withEM 385-1-1.

6-1. Preparations

a. Unformed sections.

(1) Earth surfaces. Where shotcrete is to be placedagainst earth surfaces, as in canal linings, the surfacesshould first be thoroughly compacted and trimmed to lineand grade. Shotcrete should not be placed on anysurface which is frozen, spongy, or where there is freewater. The surface should be kept damp for severalhours before shotcrete is placed.

(2) Rock surfaces. Where shotcrete is to be placedagainst rock, all loose material, debris, dirt, or otherforeign matter must be removed to allow good bondbetween the rock and the shotcrete. This may not bepossible or advisable in hazardous undergroundapplications.

(3) Concrete and masonry surfaces. Where shotcreteis to be used for repairing deteriorated concrete, it isessential that all unsound material first be removed.Chipping should continue until there are no offsets in thecavity which would cause an abrupt change in thethickness of the repair. The perimeter of the repair areamay be sawcut or chipped with a slight taper to thecenter of the area. Feather edging should be avoided.After it has been determined that the surface (whetherconcrete, masonry, or steel) to which shotcrete is to bebonded is sound, it should be prepared by drysandblasting, wet sandblasting, grinding, or high-pressurewater jetting. Just prior to receiving shotcrete, all suchsurfaces should be thoroughly cleaned. Porous surfacesshould be kept damp, but not wet, before placingshotcrete.

b. Formed surfaces.Forms should be made ofplywood sheathing, expanded metal lath, or other suitablematerial, true to line and dimension. They should be

adequately braced to ensure against excessive vibrationand constructed to permit the escape of rebound and airduring the gunning operation, particularly in the case ofthick structural members. Columns should be formedonly on two adjacent sides wherever possible.Satisfactory results may be obtained where three sidesare formed, provided the width is at least 1.5 times thedepth. Pilasters may be formed on two adjacent oropposite sides. The soffit and one side of beams shouldbe formed, and shores should be set below the soffit insuch a manner that no deflection will occur under theload to be imposed. Short, removable bulkheads may beused at intersections. The forms should be oiled ordampened and should be clean just prior to gunning.

c. Work area access.Safe, adequate scaffoldingshould be provided so that the nozzleman can hold thenozzle at the optimum angle and distance from thesurface for all parts of the work. The scaffolding shouldalso provide easy access to the shotcrete surface forscreeding and finishing operations.

d. Reinforcing steel repair.

(1) Concrete around the reinforcing should beremoved until clean, uncorroded steel is reached.Concrete behind reinforcing steel should be removed to adepth to allow proper placement from a nozzle angles notmore than 45 degrees to the surface. This depth is oftenmore than 1.5 times the bar diameter but not less than 1inch. Reinforcing that is corroded so badly that itsusable cross section is reduced must be replaced.

(2) Defective bars are removed by cutting out thedefective length and replacing with a new section ofreinforcing bar. New bars must be lapped appropriately.Alternate attaching schemes such as butt welding,mechanical splices and other means should be consideredcarefully.

(3) Anchoring new bars in the existing, soundconcrete is done by drilling holes and anchoring the endswith an epoxy grout. The anchorage must be designed tofully develop the load capacity of the bar andaccommodate edge conditions near the bar.

(4) Stirrups should be treated the same as bars. Thedesign and placement of the steel should be accomplishedto minimize interference with the shotcrete placement.All anchors and bars should be arranged in the repair sothat proper cover with shotcrete is provided.

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e. New reinforcement.

(1) Reinforcing in shotcrete is designed likeconventional concrete. Wire fabric may be used innonstructural or light structural applications to control thedevelopment and depth of shrinkage and temperaturecracking.

(2) Wire fabric can control debonding ordelamination of the shotcrete if either condition mayexist. Small bar reinforcement may be added to fabric toresist movement of the fabric during shotcreting, and toreduce the number of required fabric layers. Barreinforcement is seldom used in sections thinner than1-1/2 inches. Wire fabric may be used in sections as thinas 3/4 inch. Steel fibers may be used in lieu of wirefabric. Wire spacing should be a minimum of 2 incheson center. Fabric should be tied similarly to barreinforcement for shotcrete. Fabric sheets should belapped one and one-half spaces in all directions. Whenseveral layers of wire fabric are required, the first layeris covered with shotcrete prior to placing the next layer,with ties extending from the first layer to the next. Atleast one layer of fabric is used for each 3 inches ofshotcrete.

(3) Bar reinforcement must be sized and positionedto minimize interference with shotcreting. Generally, barsizes smaller than No. 5 should be used. Larger sizesmay be used, but great care must be taken when encasingthem with shotcrete. If possible, lapped bars should beseparated by at least three bar diameters. One layer ofreinforcement is generally sufficient for sections 8 inchesor less in thickness. Thicker sections require severallayers of bars, with the outer layer spaced to allow easyaccess to the inner layers. Bars should be rigidly tiedwith 16-gauge wire to prevent vibration of the bars thatcould cause sagging of the shotcrete or poor bond. Tiewires should be bent flat in the plane of the mesh. Largeknots of wire might become voids in shotcrete. Anchorsto support reinforcement are spaced each way at amaximum of 36 inches for floor applications, 24 inchesfor vertical and inclined applications, and 18 inches foroverhead applications. Horizontal reinforcement shouldnot be placed less than 12 inches from the ground orfloor slab, especially if loose soil or sand forms thehorizontal surface. At this height, it is difficult to shootfrom the underside of the reinforcement. There is also astrong tendency for the material stream to pick up sand,soil, or rebound from the ground, thereby creating severesand pockets.

f. Anchorage. Anchorage of shotcrete followspractice for conventional concrete.

g. Alignment control.A variety of alignment controldevices are required to establish the limits of shotcreteplacement, including ground wires, guide strips, depthgauges, depth probes, or forms. Ground wires areusually 18 or 20-gauge, high-strength steel wires attachedto a turnbuckle or spring to provide tension. Wires maybe used to establish corners of the shotcrete work, andmay be spaced at 2- to 3-foot intervals for screed guidesfor flat areas. Guide strips are wood lath attached tocrosspieces at 2- to 3-foot intervals, used similarly towires. Depth gauges, small metal or plastic devicesattached to the surface to which shotcrete is beingapplied, indicate the resulting thickness of the shotcrete.They may be left in place, and slightly covered, if theirpresence is not damaging. Depth probes are stiff steelwire rods premarked with the thickness of shotcrete,which are inserted into the shotcrete to check thickness.

6-2. Batching and Mixing

a. Equipment. Batching and mixing equipment mustbe capable of maintaining an adequate and continuousflow of uniform material. Aggregate particles should bewell coated with cement paste. Batching by mass ispreferred and should normally be required. Water maybe batched by mass or volume. For small jobs, approvalmay be given to batching by a volumetric container,provided periodic checks of mass are made, or batchingby volumetric mobile-mixing equipment.

b. Jobsite mixing.Since many shotcrete jobs have alow production rate and are in isolated locations, mixingis often done by a small drum mixer at the jobsite. Insuch cases, the mixing time should not be less than1 minute. Where other mixers are proposed, satisfactoryevidence should be presented to show they are capable ofthorough mixing. The mixer should be capable ofdischarging all batched material without any carry-overfrom one match to the next. It should be inspected andcleaned thoroughly at least twice a day, more often ifnecessary, to prevent accumulations of batched materialand minimize unplanned shutdowns.

c. Dry-mix process.

(1) The moisture content of the fine aggregateshould be such that the aggregate-cement mixture willflow through the delivery hose at a uniform rate. It

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should not be wet enough to cause slugs in the line, butdamp enough for good adhesion between the cement andaggregate and to prevent a buildup of electrostaticcharges. The optimum moisture content will dependupon the delivery equipment being used, but it isgenerally within the range of 3 to 6 percent, by dry mass,for the fine aggregate fraction. The aggregate should bedampened or dried as required to bring the moisture to asatisfactory level. Fluctuations in moisture contentshould be avoided. The nozzleman must control themixing water so that the surface of the shotcrete has aslight gloss. Too much water can cause sagging,sloughing, puddling, or drop out, especially in overheadwork. Insufficient water is indicated by a dry, dark,sandy surface appearance. This condition increasesrebound, creates sand pockets, makes finishing difficult,and can result in weak, laminated shotcrete.

(2) The preferred method of dry-mix batching forlarge shotcrete projects is to batch materials onsite on aconcurrent continuous basis. This is best done usingprebagged materials and premoisturizing equipment.However, for smaller projects it is common to batchaggregates, cement, and special materials at aconventional concrete batch plant and to mix in a transitmixer. This damp material is discharged from the transitmixer into the shotcrete gun. It is critical that the totalelapsed time from batching to shooting not exceed45 minutes during hot weather and not more than90 minutes during cool weather. For low production rateoperations these time limits result in batching only smallvolumes of dry-mix material, often 1 to 3 cubic yards.

(3) Where the cement-aggregate mixture is furnishedto the dry-mix shotcrete equipment by truck mixer in thedry state already proportioned, CRD-C 31 (ASTM C 94)applies. Where the ingredients are delivered in dry formand proportioned and mixed at the site, conventionalbatching plant operations conforming to CRD-C 31(ASTM C 94) or volumetric batching and mixing plantoperations conforming to CRD-C 98 (ASTM C 685)should be used.

(4) For mixtures containing silica fume, prebaggingof all materials should be strongly considered. Shotcrete,exceeding the time limits stated in paragraph 6-2, willtend to form balls of cement and silica fume as themixture continues to roll in the mixer drum. Theshotcrete product will exhibit higher rebound, lowerstrengths, and lower cohesion and adhesion.

d. Wet-mix process.

(1) Batching and mixing operations should generallyfollow the guidelines given in ACI 304. Where ready-mixed concrete is used, it should conform to CRD-C 31(ASTM C 94). Some pneumatic-feed guns have twochambers to permit continuous gunning. Concrete ismixed in one chamber while it is being withdrawn fromthe other. Continuous batching and mixing meeting therequirements of CRD-C 98 (ASTM C 685) may also beused. Delivery of concrete at the desired consistency anduniformity from batch to batch is essential to a goodshotcreting operation, especially in vertical and overheadapplications.

(2) Batching and mixing operations for wet-mixshotcrete are the same as batching of conventionalconcrete. Batch plants range from small single-scalemanual plants to large automated plants. Mixing is donein transit mixers or in a central mixer at the plant. Theaddition of special materials such as fibers, silica fume,polymers, and others is done as would be done forconventional concrete.

e. Admixture dispensers.For either the dry-mix orwet-mix process, admixture dispensers should receivespecial attention to ensure that the material is dispensedwithin ±3 percent of the required batch quantity and isuniformly dispersed through the mixture.

6-3. Shotcrete Application Techniques

a. Techniques and procedures. The nozzlingtechniques and procedures used in applying shotcretegreatly affect the quality of the shotcrete and the amountand composition of rebound. Rebound material maybecome entrapped in succeeding shotcrete if poornozzling techniques are followed. The entrapment ofrebound results in a decrease in the ultimate strength anddurability of the shotcrete.

b. Nozzle angle.Plane surfaces should generally beshotcreted with the nozzle held at 90 degrees to thesurface. When this principle is not followed, excessiverebound and decreased compaction usually result. Twoexceptions to this practice occur when gunning aninterior corner or when encasing reinforcing steel.Interior corners should be gunned by directing the nozzlein the plane bisecting the angle of intersection of the twosurfaces (Figure 6-1) which reduces the amount of

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rebound entrapped in the corner. Areas with reinforcingsteel should be gunned at a slight angle from each side.When gunning horizontal work, the nozzle should beheld at a slight angle from vertical so that rebound isblown onto completed work for ease of removal.

c. Nozzle distance.The optimum distance betweenthe shotcrete nozzle and the surface is generally about3 feet. Rebound increases when the nozzle is held at adistance greater than 3 feet and compaction and strengthof the shotcrete are reduced. Rebound can also increaseif the nozzle is held closer than 3 feet and no reductionin pressure and delivery rate is made. At reduceddistances, the nozzleman is more exposed to reboundingparticles.

d. Nozzle motion. A steady circular or ellipticalmovement of the nozzle across the surface is the propergunning technique (Figure 6-2). The nozzle should notbe directed toward one spot for extended periods sincethis causes increased rebound and difficulty in controllingthe thickness of the layer. When the nozzle is notconsistently moved, areas of well-compacted material areformed adjacent to areas that are poorly compacted.

(1) Overspray results when shotcrete material iscarried by the airstream but not deposited at the point ofapplication. The material has a reduced cement contentand is not consolidated by high-velocity impact resultingin a zone of undesirable low-strength material. A sandpocket results if the overspray is encased by shotcrete.Overspray can he avoided by following proper nozzlingtechniques.

(2) Horizontal and vertical corners should be filledfirst to eliminate the common collection areas foroverspray. The center of the surface being shotcretedmay then be brought to the required thickness.

e. Encasing reinforcement. Encasement ofreinforcing steel with shotcrete must be done carefully toprevent pockets of uncemented aggregates from formingbehind the bars (Figure 6-3).

(1) To prevent formation of these sand or rockpockets, the nozzle should be held close to thereinforcing bar and at a slight angle from theperpendicular to force material around and behind thebar. The front of the bar should remain clean and free ofbuildup until the entire bar is encased. A blowpipeshould be used during the gunning operation to removeaccumulation on the front of the bars and entrapped

rebound from behind the bars (Figure 6-4). Theshotcrete mixture should be slightly wetter than normal,although not so wet that there will be sloughing behindthe bars. Where bars are closely spaced, more than onebar may be shot from each location.

(2) Proper installation of reinforcing bars and meshcan reduce encasement problems and the potential formajor sand pocket voids. All obstacles to the flow of theshotcrete material stream should be kept to a minimumsize. For example, a No. 4 bar can be readily encasedby a skilled nozzleman, while a No. 8 bar would be verydifficult to properly encase.

f. Progression of work.

(1) The bondable material to which shotcrete is tobe applied should be clean and free of bond-breakingsubstances such as dirt, grease, oil, curing agents, paints,or deteriorated material. Once the surface is properlycleaned and prepared for shotcrete, a shooting techniquemust be used which does not foul or dirty the cleansurface.

(2) A thin initial coat of shotcrete should be rapidlyapplied to the selected work surface before starting thelayering of shotcrete. This initial coat protects preparedsurfaces from contamination with overspray or rebound.The work area should be of such size that the surface canbe maintained "wet" with fresh shotcrete so that initialset does not occur until after shooting of the area iscompleted. Therefore, the work area size is dependentupon sun exposure, ambient temperature, wind velocity,admixtures in the shotcrete, accessibility of the worksurface, equipment being used, and the nozzleman’sability.

(3) Once the initial bonding or wet coat is applied tothe entire work area, a second pass over the area mayproceed at a slower rate. This pass allows the formationof a thicker buildup of material over the first bondinglayer. Corners should be filled first to prevent theaccumulation of overspray and rebound, followed byapplication onto the flat areas.

(4) When the limited work area has been completed,rebound and overspray should be removed fromadjoining areas with air before the shotcrete takes initialset. This cleaning effort may be expedited by thefinisher and other laborers with trowels, shovels, brooms,and other available equipment.

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Figure 6-1. Shotcreting interior corners (Mahar, Parker, and Wuellner 1975)

Figure 6-2. Shotcrete nozzle motion (after Ryan 1973)

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Figure 6-3. Correct and incorrect methods of encasing reinforcing bar with shotcrete (paragraph A-1, ACI1991d; copyright permission granted by ACI)

6-6

CORRECT

NOZZLE CLOSE

l·'k,S: :;:~ *q 1. SHOTCRETE FORCED BEHIND BAR

BY HIGH VELOCITY.

::t: Q tq: ~ ~ 2. BACK OF BAR FULLY. ENCASED. ~

.3. FACE OF BAR STILL FREE OF

SHOT CRETE BUILDUP.

to, • . .~.

y.: ..... : .. . ·. .. . • .... ..... ·. .. .. . . . •. " . ·"'· .. · ....

. .. ·; .. . · ... · ... ..

.; ."' . .. :_·: .. ... -.·.· ~-

4.PERFECT ENCASEMENT ALMOST COMPLETED.

~ ::t: Q .......

~ 9: Cl

INCORRECT NOZZLE TOO FAR

AWAY

@ },;<=A~df~

1. SOFT IMPACT CAUSES SHOTCRETE BUILDUP ON FRONT Of" BAR.

2. HEAVY BUILD-UP ON BAR.

.3. SANDY, POROUS MATERIAL

BEHIND BAR

4. SHRINKAGE CRACK DEVELOPS

LATER AT WEAKENED SECTION.

EM 1110-2-200531 Jan 93

(5) When gunning vertical work, shotcrete should beapplied from the bottom up. For thick walls, "shelf" or"bench" gunning may be used, where, instead of gunningdirectly against the vertical surface, a thick layer ofshotcrete is built up from the bottom, maintaining a45-degree slope.

g. Protection. Shotcrete cannot normally be appliedduring periods of rain, snow, or high wind. Rain maywash out the cement leaving a sandy surface, or it maysaturate the shotcrete and cause sloughing or sagging.Strong winds will separate the material between thenozzle and the point of deposit, reducing strength. Ifproper shields cannot be erected to reduce the effects ofthe wind, the shotcreting should be discontinued.Because shotcrete rebound, overspray, and dust candamage adjacent surfaces, protection for these surfacesmay be needed. Means of protection include plastic orcloth covers, masking materials, temporary coatings, orplywood or other wood. If protection is not feasible,then adjacent surfaces should be cleaned before thecontaminant hardens.

h. Construction joints. Construction joints arenormally tapered about one-half of the shotcretethickness or a maximum of 1 inch thick to an edge, overa width of 10 to 20 inches. Square joints can be cut by atrowel at initial set. Ordinarily, square joints should beavoided in shotcrete construction because they form atrap for overspray and rebound. However, if the jointwill be subjected to compressive stress, square or buttjoints may be required. Steps must be taken to avoid orremove trapped rebound at the joint. The entire jointshould be thoroughly cleaned and wetted prior to theapplication of additional shotcrete.

i. Contraction joints. These joints may be requiredin some applications, such as canal linings, to controlshrinkage cracking of the shotcrete. The joints may becreated by prepositioning strips of plastic or metal, andleaving them in place, or by sawcutting the newlyhardened shotcrete. Contraction joints are not generallyincorporated in such work as tunnel linings or slopeprotection.

Figure 6-4. Use of a blowpipe in removing rebound for proper encasement ofreinforcing bars (after Ryan 1973)

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j. Waterstop. Due to the difficulty of placingshotcrete around waterstops, use of waterstops inshotcrete applications should be avoided.

k. Multiple layers. When a layer of shotcrete is tobe covered by a succeeding layer, it should first beallowed to develop its initial set. Then all loose materialand rebound should be removed by brooming, scraping,or other means. Surface deposits which take a final setshould be removed by sandblasting and the surfacecleaned with an air-water jet.

l. Time limitations. The time from the batching ofshotcrete to final placement should not exceed45 minutes during warm weather, when ambienttemperatures exceed 80 °F. When ambient temperaturesare below 80 °F, the time may be extended to amaximum time of 90 minutes. These requirements applyto both wet-mix and dry-mix shotcrete. These timelimits may need to be shortened to accommodateadditions of polymers, silica fume, or other additives.

6-4. Rebound

a. Rebound is aggregate and cement paste thatbounce off the surface during the application of shotcretebecause of collision with the hard surface, thereinforcement, or the aggregate particles themselves. Theamount of rebound varies with the position of the work,air pressure, cement content, water content, maximumsize and grading of aggregate, amount of reinforcement,and thickness of layer. The percent of rebound fromconventional cement-aggregate shotcrete by three generaltypes of work surfaces is shown in Table 6-1.

Table 6-1Rebound from Conventional Cement-Aggregate Shotcrete

Percent of Rebound, by Mass

Work Surfaces Dry-mix Wet-mix

Floors or slabs 5-15 0-5

Sloping and verticalwalls 5-25 5-10

Overhead work 25-50 10-20

b. Rebound will be less for small-aggregate mixturesand more for large-aggregate mixtures. Rebound ofsilica-fume shotcrete mixes may be as much as50 percent less than other mixtures because of the highlycohesive nature of silica fume.

c. Initially, the percentage of rebound is large butbecomes less after a cushion of fresh shotcrete has beenbuilt up. While rebound contains some cement paste, itconsists mostly of the coarser aggregate particles.Consequently, the cement content of the in-placeshotcrete is higher because of aggregate loss fromrebound. This increases the strength of the shotcrete andalso increases the tendency toward shrinkage andsubsequent shrinkage cracking. Rebound should not beworked back into the construction by the nozzleman. Ifit does not fall clear of the work, it must be removed.Trapped rebound, if not removed, creates sandy, porousareas and laminations in the cross section which are agreat detriment to shotcrete quality. Rebound should notbe salvaged and included in later batches because of thedanger of contamination. Also, the cement content, stateof hydration, and the grading of the aggregate in reboundare all variable and unpredictable.

d. Measurement of rebound from test panels shouldbe considered before beginning the shotcrete operation.Rebound can be collected in traps placed on the groundin front of the panel. The percentage of rebound isdetermined by dividing the mass of the rebound materialby the mass of the shotcrete delivered through the nozzleand multiplied by 100.

e. Shotcrete operations pose the threat of injury fromhigh velocity particles of rock, cement, and dust strikingeyes and other exposed areas of the body. Reboundedparticles constitute the same type of hazard as thematerials in the shotcrete stream, but to a lesser degreesince impact on the surface usually reduces theirvelocities. Suitable headgear must be worn in thevicinity of the nozzling operation. The nozzleman is lesslikely to be injured than a workman who stands close tothe nozzle but at right angles to the material stream. Useof protective clothing and safety equipment will helpprevent serious injury from rebound.

6-5. Finishing

a. The natural gun finish is preferred from thestandpoints of both structural soundness and durability.Further finishing may disturb the section, harming thebond between the shotcrete and reinforcement or betweenthe shotcrete and the underlying material, and creatingcracks in the shotcrete. Additional finishing may also bedifficult to accomplish, especially for the drier mixtures.However, the natural gun finish is unacceptable for somestructures because of its roughness. Where greatersmoothness or better appearance is required, specialfinishes, as listed, must be applied.

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b. After the surface has taken its initial set(crumbling slightly when cut), excess material outside theforms and ground wires may be sliced off using asharp-edged cutting screed. Upward cutting motionshave a tendency to pull the material apart. The groundwires should then be removed, and the irregularitiesfloated. The finish may be left in this condition, or itmay be broomed.

c. If a still finer finish or better appearance isdesired, a flash coat may be used. This is a thin surfacecoating containing finer sand than normal and laid onwith an application nozzle held well back from the work.It should be applied to the shotcrete surface as soon aspossible after the screeding.

d. If desired, the as-gunned finish or flash coat maybe followed by surface finishing using one or more ofthe following tools:

(1) Wood float, giving a granular texture.

(2) Rubber float, giving a coarse texture and finish.

(3) Steel trowel, giving a very smooth finish.

6-6. Curing and Protection

a. Proper curing of shotcrete is extremely importantto ensure proper hydration, matrix and bond strengthdevelopment, and to prevent cracking due to dryingshrinkage. Note that the rate of bond strengthdevelopment is significantly slower than compressive ortensile strength development. The curing procedures ofACI Standard 308 (paragraph A-1, ACI (1991c)) shouldbe followed. The thin sections commonly used inshotcrete construction are particularly susceptible todrying shrinkage. Surfaces should be kept continuouslymoist for at least 7 days. After this time interval, the

shotcrete has gained sufficient tensile strength to resistshrinkage strains, and the permeability near its exposedsurface is low enough to minimize loss of water from theinterior of the section. Membrane curing is permissibleonly when drying conditions are not severe, where noadditional shotcrete or paint is to be applied, and where itis esthetically acceptable. Coverage rates of roughshotcrete surfaces should be twice what is used onconventional concrete surfaces.

b. Silica-fume shotcrete must always be continuouslymoist cured to assure proper strength gain and surfacedurability. It is common to specify the use of fognozzles to maintain a moist condition on all newsurfaces. While less convenient, sprinklers and soakerhoses can provide adequate curing so long as it can beassured that all the surface area is maintained in a moistcondition.

6-7. Repair of Surface Defects in New Shotcrete

a. Surface defects must be repaired as soon aspossible after initial placement of the shotcrete. Allshotcrete which lacks uniformity, which exhibitssegregation, honeycombing, or lamination, or whichcontains any dry patches, slugs, voids, or sand pocketsmust be removed and replaced with fresh shotcrete.

b. Core holes are not to be repaired with shotcrete.Instead, they should be filled with a dry-pack mortar.

c. Where surface crazing, shrinkage cracks, or lowstrengths occur, additional analysis is required todetermine the effect upon the structure. In some cases,no remedial action may be required; in others a surfacetreatment with a polymer may be satisfactory. In caseswhere the performance of the structure is significantlydegraded, the affected shotcrete areas must be removedand replaced with sound shotcrete.

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Chapter 7Quality Control

7-1. General Considerations

Shotcrete is a unique concrete material with manyunusual applications that require careful attention todetails. It is essential that quality control procedures beestablished to assure that the final product functions asdesigned and that it has the desired life expectancy. Thecontract specifications should clearly call out theContractor’s responsibilities for verifying that theproposed materials, equipment, methods, etc. will meetthe requirements of the contract specifications. Requiredsubmittals and test reports should be clearly stated in thespecifications. ER 1180-1-6 should be followed inregard to the format and details of a contractor qualitycontrol (QC) program. The following discussions pertainto technical aspects of shotcrete and should be consideredwhen preparing contractor QC specification requirementsand when reviewing the Contractor’s QC plan.

7-2. Preproduction Phase

Prior to start of production of shotcrete for anypermanent work, the following submittals and test reportsshould be furnished and the following testing performedby the Contractor to verify that his materials, methods,equipment, and procedures meet the contractrequirements.

a. Submittals.

(1) Cementitious materials. Manufacturer’s certifiedtest results should be furnished to verify that the cementand pozzolan meet the contract requirements.Appropriate test results should be furnished to verify thatsilica fume meets the contract requirements.

(2) Aggregates. Test data should be furnished toverify that the fine and coarse aggregates meet thequality and grading requirements of the contract.

(3) Admixtures and curing compound. Amanufacturer’s certificate of compliance should befurnished to verify that the air-entraining admixture,retarding admixture, water-reducing admixture,accelerating admixture, and curing compound meet thecontract requirements.

(4) Fibers and reinforcement. A manufacturer’scertificate should be furnished to verify that the proposedfibers and reinforcement meet the requirements of thespecifications.

(5) Mixture proportions. Test data should befurnished to verify that the Contractor’s proposed mixtureproportions will produce shotcrete that meets the qualityrequirements of the specifications. Test specimensshould contain the materials proposed for the project andshould be obtained from test panels shot with theequipment and by a nozzleman that will be used for thepermanent work.

(6) Accelerator compatibility test. When anaccelerator is proposed to be used in the shotcrete, testdata per CRD-C 625 (ASTM C 1141) should befurnished to verify that the combination of cement andaccelerator meet the contract requirements for initial andfinal set times.

(7) Nozzleman certification. ACI certifies shotcretenozzlemen. If required by the specifications, a currentcertification for each nozzleman who will be placingshotcrete in permanent work should be submitted.

(8) Equipment. If determined to be necessary by thedesigner and so stated in the contract, the equipment andlayout of the proposed plant for producing, conveying,and placing the shotcrete should be furnished to verifyconformance with the requirements of the specifications.

(9) Curing and protection. The method of providingthe required curing and protection of the in-placeshotcrete should be submitted. Hot weather and coldweather protection plans should be submitted.

b. Test panel fabrication, testing, and evaluation.Test panels must be scheduled to be shot early in aproject to allow sufficient time for evaluation of thepanels prior to start of production of shotcrete for thepermanent work. Test panel sizes and configurations aredetailed in Chapter 5. Test panels are necessary forevaluation of the proposed shotcrete mixture and toevaluate the qualifications of the proposed nozzleman.Specimens should be sawn or cored from the test panelto verify the contract requirement for strength. Thespecimens and the test panel should be visually examinedfor signs of laminations, sand streaks, aggregate pockets,reinforcing steel not completely surrounded by shotcrete,

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and any other indications of either mixture proportionproblems or nozzleman workmanship.

7-3. Production Phase

An ongoing program of testing should be performed bythe Contractor to verify that the materials, methods, andin-place shotcrete meet the requirements of the contractdocuments. The specifications should clearly state theminimum types of tests that are required, the minimumfrequency of performing each test, a procedure forreporting the results of the tests, and a procedure forcorrecting any deficiencies (Table 7-1).

a. Materials.

(1) Cementitious materials. Manufacturer’s certifiedtest results for the cement, pozzolan, and appropriate testdata for silica fume should be furnished at the intervalspecified and whenever a change in the appearance orperformance of the material is suspected.

(2) Aggregates.

(a) Quality. Test data should be furnished to verifythat the quality of the aggregates meets the requirementsof the specifications. Test data should be submitted atestablished intervals and whenever a change in theappearance or performance of the material is suspected.

(b) Grading. The grading of each aggregate groupshould be verified by testing according to CRD-C 103(ASTM C 136) at established intervals and whenever achange in the appearance or performance of the materialis suspected. Changes in the grading of an aggregatewill cause a change in the water requirements of themixture with attendant changes in the strength andplacing characteristics of the shotcrete.

(c) Moisture content. The moisture content of eachaggregate group must be known to calculate the amountof free water to be added to each batch of shotcrete. Themoisture contents should be established prior to start ofeach shift and whenever a change is made in stockpilesources.

(3) Admix tu res and cu r ing compound .Manufacturers’ certificates of compliance for the air-entraining admixture, retarding admixture, water-reducingadmixture, accelerating admixture, and curing compoundshould be furnished at an established interval andwhenever a change in the appearance or performance ofthe material is suspected.

b. Surface preparation.The Contractor’s ability toprepare surfaces according to the requirements of thespecifications should be verified during each shift. Noshotcrete should be placed until surface preparations arecompleted. Bonding of the shotcrete layer to theunderlying stratum is essential for proper performanceand longevity.

c. Shotcrete.

(1) Strength. The strength of the shotcrete shouldbe verified at established intervals. The method ofobtaining samples, the method of testing, the frequencyof testing, and the required strength should be clearlystated in the contract specifications.

(a) Test panels. A test panel should be shot at leastonce a shift. The panel should be shot by a nozzlemanwho is placing shotcrete in permanent work shotcrete.The panel should be at least 18 by 18 by 3 inches. Thetest panel should be cured at the project site inaccordance with the contract requirements until it hasattained sufficient strength to allow movement to thetesting laboratory. Curing should continue in the testlaboratory until specimens are obtained from the panel.Cores or beams should be taken from the panel inaccordance with the provisions of CRD-C 27 (ASTMC 42). Cores are used to verify the compressive strengthof nonfiber reinforced shotcrete, and beams are used toverify the flexural strength of fiber-reinforced shotcrete.

(b) In-place samples. At established intervals andwhenever deemed necessary by the Contracting Officer,cores or beams should be obtained from the in-placeshotcrete to verify the strength. The samples should becured and tested in a manner similar to that of test panelsamples.

(2) Mixture proportions. The mixture proportions ofthe shotcrete should be checked regularly to verify thatthe original proportions are being maintained. This isgenerally accomplished by verifying that the batchweights, especially the cementitious materials and waterweights, are as required.

(3) Air content. Wet-mix shotcrete is generallyrequired to have a specified air content as determined byCRD-C 41 (ASTM C 231). The air content should bedetermined at regular intervals and at locations asspecified. The air content specified in the contractdocuments is higher than required for durableconventional concrete and allows for about 50 percent of

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7-3

Table 7·1 Quality Control Testing Requirements

Cementious Materials

Aggregate Quality Quality Grading Particle Shape Moisture Content

Unhardened Properties Air Content Slump Mix Proportions Rebound Thickness

Property/Activity

Hardened Properties Fabricate Test Panels Drill In-situ Cores Compression Stength Flexural Strength Toughness Surtace Roughness Delaminations

Mill Test

Test Procedure

CRD-C 133 (ASTM C 33) CRD-C 133 (ASTM C 33) CRD-C 119 (ASTM D 4791) CRD-C 113 (ASTM C 566)

CRD-C 41 (ASTM C 231) CRD-C 5 (ASTM C 143)

per specs per specs

per specs CRD-C 27 (ASTM C 42) CRD-C 14 (ASTM C 42/C 39) CRD-C 16 (ASTM C 42/C 78) CRD-C 65 (ASTM C 1018) per specs per specs

Frequency

per 400 tons of cement

Initial Per shift Initial Daily

Per batch Per batch Per shift Daily Per 50 tt2

Per shift 3 per 2,500 tt2 3 per 2,500 tt2 2 per 5,000 tt2 3 per 5,000 tt2 2 per 1,000 tt2 1 per 25 tt2

Comment

Increase if necessary

Wet-mix only Wet-mix only

Probe shotcrete or check gauge wires

Fiber-reinforced shotcrete only

* Table values are only a guide. Testing frequency must be based on an evaluation of testing costs, criticality of pertormance, and the nature of the application.

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the air to be lost during the delivery and shooting of theshotcrete. The specification must detail how air contentis to be determined. If sampled at the pump, the test isperformed as detailed in CRD-C 41 (ASTM C 231).

(4) In-place thickness. Gauge wires or studs shouldbe set prior to placing shotcrete to facilitate placing ofthe required thickness. It is best to verify thickness bymeasuring the offset of the gauge wires since laterprobing of the in-place shotcrete may be very difficult.The in-place thickness of the shotcrete may be verifiedby probing the fresh shotcrete with a sharp tool. Thinareas should be corrected by immediate application ofadditional material. Cores of hardened shotcrete may bedirected to be taken by the Contracting Officer to verifyareas of suspect thickness.

(5) Rebound testing. It is advantageous toperiodically determine the amount of shotcrete that isrebounding from the placement surfaces. This can bedone by designating a placement area and collecting allthe rebound material after the placement is complete.The percent of rebound can be calculated by determiningthe volume of material shot and the volume of materialcollected.

(6) Curing and protection. The contractor shouldverify that the required curing and protection of theshotcrete is being furnished. Proper curing is importantdue to the generally low water content of shotcrete. Anypremature drying could impair the hydration process.Proper protection during hot or cold weather is essentialto proper hydration of shotcrete.

(7) Nondestructive testing. The uniformity andquality of in-place shotcrete may be assessed by

nondestructive testing devices such as impact hammers orprobes (CRD-C 22 (ASTM C 805) and CRD-C 59(ASTM C 803)), ultrasonic equipment (CRD-C 51(ASTM C 597)), and pull out devices (CRD-C 78(ASTM C 900)). The use of such devices should be atthe direction of the Contracting Officer and should beused to identify areas of suspect quality and relativestrength, not for actual strength determination.

(8) Delamination testing. Where appropriate,complete shotcrete coatings should be checked forcomplete bond to the substrate and bond between eachshotcrete layer. This can be done using a small hammeron the surface. The contract should require that alldelaminated areas be removed and shotcrete reapplied.

(9) Surface tolerances. Some applications mayrequire that exacting surface variation tolerances be met.Verifying that a surface meets a tolerance is best doneusing the specified length straight-edge and measuringthe gap below the edge. The specification should beclear that this method will be the verification method.

(10) Visual inspection. The quality of the shotcreteshould be thoroughly evaluated by visual inspection.Surfaces should be inspected for uniformity, voids at thesurfaces, varying finish conditions, dry conditions,seepage of water, cracking, and damaged sections.

7-4. Corrective Actions

When a submittal or test report indicates that a materialor product fails to meet the contract requirements, thecorrective actions specified in the contract documentsshould be initiated immediately.

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Chapter 8Quality Assurance

8-1. General Considerations

a. Quality Assurance (QA) activities on a shotcreteproject should be directed to obtaining compliance withthe contract requirements. The quality of the materialsused in the production of the shotcrete and of thein-place shotcrete are established during the design stageof the project and should have been clearly stated in thecontract documents.

b. A memorandum entit led "EngineeringConsiderations and Instructions for Field Personnel"should be prepared by the designer in accordance withEM 1110-2-2000. This memorandum outlines thedesigner’s intent and highlights the areas of specialconcern during construction. If any doubts exist byconstruction personnel as to the required quality, theyshould be resolved with the designer as early in theproject as possible.

c. Qualified QA personnel with previous experienceon shotcrete projects should be assigned to the project.ER 1180-1-6 should be followed in preparing a QA Plan.The following discussions pertain to technical aspects ofshotcrete and should be incorporated into the plan.

8-2. Preproduction Phase

a. Submittals.Prior to start of production ofshotcrete for any permanent work, the required material,equipment, and procedural submittals should be reviewedby the appropriate Corps of Engineers representatives toverify compliance with the contract requirements. Onlarger projects, government verification of cementitiousmaterials properties should be considered.

b. Mixture proportioning evaluation.Test panelsshot to verify the proposed mixture performance shouldbe visually examined by QA personnel to confirmuniformity of the shotcrete. Specimens should be takenfrom the test panels to verify that the specified strengthis being attained. The specimens may be taken by eitherQC or QA personnel, but strength testing should beperformed by a Corps of Engineers division laboratory orthe project laboratory.

c. Nozzleman certification.All nozzlemen shall beACI certified. Test panels shot to evaluate a

nozzleman’s qualifications should be thoroughlyexamined by a QA representative experienced inshotcrete work. Some panels should contain reinforcingor embedded items that will be included in the permanentwork. Panels should be sawn into strips to allowexamination of the interior portions of the panels. Panelsshould be homogeneous without lenses or pockets ofaggregate and all reinforcing and embedded items shouldbe completely encased in dense shotcrete. The quality ofdry-mix shotcrete is particularly dependent on the skill ofthe nozzleman, because his ability to control the amountof water being added to the mixture and to shoot testpanels to quality is essential.

d. Shotcrete demonstration.The same test panelevaluation to certify the nozzleman serves to approve theproduction and placement process.

8-3. Production Phase

An ongoing program of QA inspections and testing willbe required to verify continued conformance with thecontract requirements. Consistent materials, mixtureproportions, and production methods are necessary foruniform in-place shotcrete.

a. Submittals.

(1) Manufacturer’s certificate. Manufacturer’scertified test results for the cementitious materials,admixtures, curing materials, reinforcement, and fibersshould be reviewed to verify continued conformance withthe contract requirements. Any changes in theappearance or performance of any of these materialsshould require additional verification by the supplier ortesting by the QC laboratory.

(2) Test reports. Data from test reports must bereviewed to determine contract compliance and, moreimportantly, product performance. Consistent andvigilant review of data is the best method to spot trendsin material quality that may later become a problem.

b. Testing. Depending on the size and criticality ofthe project, QA testing of materials and shotcrete may berequired to verify compliance with contract requirements.These tests are in addition to QC tests. They will alsoserve to verify the ability of the QC laboratory toproduce valid test data.

c. Visual Inspection. The quality of the shotcreteshould be thoroughly evaluated by visual inspection.Surfaces should be inspected for uniformity, voids at the

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surfaces, varying finish conditions, dry conditions,seepage of water, cracking, and damaged sections.

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Appendix AReferences

A-1. Required Publications

1ER 1180-1-6Construction Quality Management

1EM 385-1-1Safety and Health Requirements Manual

1EM 1110-2-2000Standard Practice for Concrete

1CW-03361Shotcrete

2US Army Engineer Waterways Experiment Station1949US Army Engineer Waterways Experiment Station.1949. Handbook for Concrete and Cement,withquarterly supplements (all CRD-C designations),US Army Engineer Waterways Experiment Station,Vicksburg, MS.

3American Concrete Institute 1991aAmerican Concrete Institute. 1991a. "ChemicalAdmixtures for Concrete," ACI Report No. 212.3R-89,ACI Manual of Concrete Practice,Part 2, Detroit, MI.

3American Concrete Institute 1991bAmerican Concrete Institute. 1991b. "Guide forMeasuring, Mixing, Transporting, and Placing Concrete,"ACI Report 304R-89,ACI Manual of Concrete Practice,Part 2, Detroit, MI.

1Reference published by Department of the Army andavailable through USACE Command InformationManagement Office sources.2All Corps of Engineers publications are available oninterlibrary loan from the Research Library, US ArmyEngineer Waterways Experiment Station, ATTN:CEWES-IM-MI-R, 3909 Halls Ferry Road, Vicksburg,MS 39180-6199.3Reference available through American ConcreteInstitute, PO Box 19150, Detroit, MI 48219.4Reference available through American Society forTesting and Materials, 1916 Race Street, Philadelphia,PA 19103.

3American Concrete Institute 1991cAmerican Concrete Institute. 1991c. "Standard Practicefor Curing Concrete," ACI Report No. 308R-86,ACI Manual of Concrete Practice,Part 2, Detroit, MI.

3American Concrete Institute 1991dAmerican Concrete Institute. 1991d. "Guide toShotcrete," ACI Report No. 506R-90,ACI Manual ofConcrete Practice,Part 5, Detroit, MI.

3American Concrete Institute 1991eAmerican Concrete Institute. 1991e. "State-of-the-ArtReport on Fiber Reinforced Shotcrete," ACI ReportNo. 506.1R-84, (Reapproved 1989),ACI Manual ofConcrete Practice,Part 5, Detroit, MI.

American Society for Testing and Materials

4ASTM C 33 (CRD-C 133)Standard Specification for Concrete Aggregates

4ASTM C 42 (CRD-C 27)Standard Test Method for Obtaining and Testing DrilledCores and Sawed Beams of Concrete

4ASTM C 94 (CRD-C 31)Standard Specification for Ready-Mixed Concrete

4ASTM C 136 (CRD-C 103)Standard Method for Sieve Analysis of Fine and CoarseAggregates

4ASTM C 150 (CRD-C 201)Standard Specification for Portland Cement

4ASTM C 231 (CRD-C 41)Standard Test Method for Air Content of Freshly MixedConcrete by the Pressure Method

4ASTM C 494 (CRD-C 87)Standard Specification for Chemical Admixtures forConcrete

4ASTM C 597 (CRD-C 51)Standard Test Method for Pulse Velocity ThroughConcrete

4ASTM C 618 (CRD-C 255)Standard Specification for Fly Ash and Raw or CalcinedNatural Pozzolan for Use as a Mineral Admixture inPortland Cement Concrete

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4ASTM C 685 (CRD-C 98)Standard Specification for Concrete Made by VolumetricBatching and Continuous Mixing

4ASTM C 803 (CRD-C 59)Standard Test Method for Penetration Resistance ofHardened Concrete

4ASTM C 805 (CRD-C 22)Standard Test Method for Rebound Number of HardenedConcrete

4ASTM C 900 (CRD-C 78)Standard Test Method for Pullout Strength of HardenedConcrete

4ASTM C 1018 (CRD-C 65)Standard Test Method for Flexural Toughness and First-Crack Strength of Fiber-Reinforced Concrete (UsingBeam With Third-Point Loading)

4ASTM C 1141 (CRD-C 625)Standard Specification for Admixture for Shotcrete

A-2. Related Publications

3American Concrete Institute 1974American Concrete Institute. 1974. "Use of Shotcretefor Underground Structural Support," Publication SP-45,Detroit, MI.

3American Concrete Institute 1980American Concrete Institute. 1980. "Performance ofConcrete in Marine Environment," Publication SP-65,Detroit, MI.

3American Concrete Institute 1981aAmerican Concrete Institute. 1981a. "ShotcreteApplications," Concrete International: Design andConstruction,Vol 3, No. 1, pp 23-109, Detroit, MI.

3American Concrete Institute 1981bAmerican Concrete Institute. 1981b. "Application andUse of Shotcrete," Compilation No. 6, Detroit, MI.

3American Concrete Institute 1991aAmerican Concrete Institute. 1991a. "Specifications forStructural Concrete for Buildings," ACI ReportNo. 301R-89,ACI Manual of Concrete Practice,Part 3,Detroit, MI.

3American Concrete Institute 1991bAmerican Concrete Institute. 1991b. "StandardSpecification for Bonding Plastic Concrete to HardenedConcrete with a Multi-Component Epoxy Adhesive,"ACI Report No. 503.2-79 (Revised 1986),ACI Manual ofConcrete Practice,Part 5, Detroit, MI.

3American Concrete Institute 1991cAmerican Concrete Institute. 1991c. "Specification forMaterials, Proportioning, and Application of Shotcrete,"ACI Report No. 506.2-90 (Revisions), Copyright 1972,1982, ACI Manual of Concrete Practice,Part 5, Detroit,MI.

3American Concrete Institute 1991dAmerican Concrete Institute. 1991d. "Guide toCertification of Shotcrete Nozzlemen," ACI ReportNo. 506.3-82,ACI Manual of Concrete Practice,Part 5,Detroit, MI.

4American Society for Testing and Materials 1978American Society for Testing and Materials. 1978."Significance of Tests and Properties of Concrete andConcrete-Making Materials," ASTM STP 169B,Philadelphia, PA.

4American Society for Testing and Materials 1992American Society for Testing and Materials. 1992."Standard Specification for Epoxy-Resin-Basin BondingSystems for Concrete, "Designation C-881-90,1992Annual Book of ASTM Standards,Philadelphia, PA; alsopublished as CRD-C 595,Handbook for Concrete andCement(with quarterly supplements), US Army EngineerWaterways Experiment Station, Vicksburg, MS.

2Brekke, Einstein, and Mason 1976Brekke, T. L., Einstein, H. H., and Mason, R. E. 1976(Jun). "State-of-the-Art Review of Shotcrete," ContractReport S-76-4, US Army Engineer WaterwaysExperiment Station, Vicksburg, MS.

3Crom 1966Crom, T. R. 1966. "Dry-Mix Shotcrete Practice,"Shotcreting, SP-14, pp 15-32, American ConcreteInstitute, Detroit, MI.

3Crom 1981Crom, T. R. 1981 (Jan). "Dry-Mix Shotcrete Nozzling,"Concrete International: Design and Construction,Vol 3,No. 1, pp 80-93, American Concrete Institute, Detroit,MI.

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3Fredricks, Saunders, and Broadfoot 1966Fredricks, J. C., Saunders, N. R., and Broadfoot, J. T.1966. "Recent Developments in Positive DisplacementShotcrete Equipment,"Shotcreting, SP-14, pp 75-83,American Concrete Institute, Detroit, MI.

3Gopalara tnam, Shah, Batson, Cr iswel l ,Ramakrisknan, and Wecharatana 1991Gopalaratnam, V. S., Shah, S. P., Batson, G. B.,Criswell, M. E., Ramakrishnan, V., and Wecharatana, M.1991 (Jul-Aug). "Fracture Toughness of FiberReinforced Concrete,"ACI Materials Journal, pp 339-353, American Concrete Institute, Detroit, MI.

3Hoffmeyer 1966Hoffmeyer, T. A. 1966. "Wet-Mix Shotcrete Practice,"Shotcreting, SP-14, pp 59-74, American ConcreteInstitute, Detroit, MI.

Holland 1987Holland, T. C. 1987 (Mar). "Working with Silica FumeConcrete," Concrete Construction,Vol 32, No. 3,Addison, IL.

5Krantz 1984Krantz, Gary W. 1984. "Selected Pneumatic Gunites forUse in Underground Mining: A ComparativeEngineering Analysis," Bureau of Mines InformationCircular/1984, 64 pp, United States Department ofInterior, Washington, DC.

4Luther 1989Luther, Mark D. 1989. "Microsilica (Silica Fume)Concrete Durability in Severe Environments,"Proceedings of the Structural Congress 1989, AmericanSociety of Civil Engineers, New York, NY, pp 95-105.

5Mahar, Parker, and Wuellner 1975Mahar, J. W., Parker, H. W., and Wuellner, W. W. 1975(Aug). "Shotcrete Practice in UndergroundConstruction," Report No. FRA-OR&D 75-90,US Department of Transportation, Washington, DC.

5Reference available from National Technical InformationService, Springfield, VA 22151.6Reference available from 11 Grosvenor Crescent,London, SWIX, 7EE, England.

2McDonald 1991McDonald, James E. 1991 (Mar). "Properties of SilicaFume Concrete," Technical Report REMR-CS-32,US Army Engineer Waterways Experiment Station,Vicksburg, MS.

3Morgan 1988Morgan, D. R. 1988 (Jan). "Dry-Mix Silica FumeShotcrete in Western Canada,"Concrete International:Design and Construction,Vol 10, No. 1, pp 24-32,American Concrete Institute, Detroit, MI.

5Morgan, McAskill, Richardson, and Zellers 1989Morgan, D. R., McAskill, N., Richardson, B. W., andZellers, R. C. 1989. "A Comparative Evaluation ofPlain, Polypropylene Fiber, Steel Fiber and Wire MeshReinforced Shotcretes," Transportation Research Record,No. 1226, Concrete and Concrete Construction,Transportation Research Board, National ResearchCouncil, Washington DC, pp 78-87.

Prestressed Concrete Institute 1981Prestressed Concrete Institute. 1981 (Jan-Feb)."Recommended Practice for Glass Fiber ReinforcedConcrete Panels,"Journal of Prestressed ConcreteInstitute,Vol 26, No. 1, pp 25-93.

3Reading 1981Reading, T. J. 1981 (Jan). "Durability of Shotcrete,"Concrete International: Design and Construction,Vol 3,No. 1, pp 27-33, American Concrete Institute, Detroit,MI.

3Rutenbeck 1974Rutenbeck, Todd. 1974. "New Developments inIn-Place Testing of Shotcrete,"Use of Shotcrete forUnderground Structural Support,SP-45, pp 246-262,American Concrete Institute, Detroit, MI.

6Ryan 1973Ryan, T. F. 1973. Gunite - A Handbook for Engineers,Cement and Concrete Association, London, England.

2Tynes and McCleese 1974Tynes, W. O., and McCleese, W. F. 1974 (Jul)."Investigation of Shotcrete," Technical Report C-74-5,US Army Engineer Waterways Experiment Station,Vicksburg, MS.

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Appendix BGlossary of Terms

AcceleratorA substance which, when added to concrete, mortar, orgrout, increases the rate of hydration of a hydrauliccement; shortens the time of setting; or increases the rateof hardening or strength development, or both.

AdmixtureA material other than water, aggregate, hydraulic cement,or fiber reinforcement used as an ingredient of concreteor mortar and added to the concrete immediately beforeor during its mixing.

Air RingPerforated manifold in the nozzle of wet-mix shotcreteequipment through which high-pressure air is introducedinto the material flow.

Aspect RatioA term used to describe the geometry of an individualfiber; it is the ratio of the length of a fiber to theequivalent diameter; the equivalent diameter is thatcircular area that is equal in area to the cross-sectionalarea of the fiber.

Bench GunningWhen building up thick sections of vertical work,shotcrete is applied against the advancing top surface ofthe shotcrete rather than directly against the verticalsurface, the top surface of the shotcrete is maintained ata 45-degree slope. (Also known as shelf gunning.)

BlowpipeAir jet operated by the nozzleman’s helper in shotcretegunning to keep rebound or other loose material out ofthe work.

Build UpGunning of shotcrete in successive layers to form athicker mass.

BulkingIncrease in the bulk volume of a quantity of sand in amoist condition over the volume of the same quantity dryor completely inundated.

Cutting ScreedSharp-edged tool used to trim shotcrete to a finishedoutline.

Delivery HoseHose through which shotcrete passes; also known as amaterial or conveying hose.

Dry-Mix ShotcretePneumatically conveyed shotcrete in which most of themixing water is added at the nozzle. (See alsoPneumatic Feed.)

Feed WheelMaterial distributor or regulator in certain types ofshotcrete equipment.

Finish CoatFinal thin coat of shotcrete applied preparatory to handfinishing.

Flash CoatA light coat of shotcrete used to cover minor blemisheson a concrete surface applied from a distance greaterthan normal.

Ground WireSmall-gauge high-strength steel wire used to establishline and grade as in shotcrete work; also called alignmentwire or screed wire.

Gun(1) Shotcrete material delivery equipment used toreceive materials and deliver them to the nozzle; theequipment often consists of double chambers underpressure (equipment with a single-pressure chamber isused to some extent). (2) A pressure cylinder used topneumatically propel freshly mixed concrete.

Gun FinishUndisturbed final layer of shotcrete as applied from thenozzle, without hand finishing.

Gunite (former trademark)A method of applying dry-mix shotcrete; term sometimesused for dry-mix shotcrete.

GunmanWorkman on a shotcreting crew who operates thedelivery equipment.

GunningThe act of applying shotcrete; ejection of material fromthe nozzle and impingement on the surface to be gunned.(Sometimes called shooting.)

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EM 1110-2-200531 Jan 93

Gunning PatternConical outline of the material discharge stream inshotcrete operation.

Hamm TipA flared shotcrete nozzle having a larger diameter atmidpoint than either inlet or outlet; also called apremixing tip.

NozzleA metal or rubber tip attached to the discharge end of aheavy, thick-wall rubber hose from which a continuousstream of shotcrete is ejected onto the placement.

Nozzle VelocityThe rate at which shotcrete is ejected from the nozzle,usually stated in feet per second or meters per second.

NozzlemanThe operator who manipulates the nozzle and controlsplacement of the shotcrete; in the case of dry-mixshotcrete, the nozzleman also controls the water contentof the shotcrete.

Pneumatic FeedShotcrete delivery equipment in which material isconveyed by a pressurized air stream.

Positive Displacement Concrete PumpWet-mix shotcrete delivery equipment in which thematerial is pushed through the material hose in a solidmass by a piston, auger, or other displacement typeequipment.

ReboundAggregate and cement or wet shotcrete which bouncesaway from a surface against which shotcrete is beingprojected.

Sand LensesA general term for areas in the shotcrete that are eithervoids or pockets of aggregate that have segregated fromthe cement, sand lenses are oriented in planes parallel to

the layering of the shotcrete, analogous to rock pocketsor honeycomb in conventional concrete.

Sand PocketA zone in concrete or mortar containing sand withoutcement.

Shelf GunningWhen building up thick sections of vertical work,shotcrete is applied against the advancing top surface ofthe shotcrete rather than directly against the verticalsurface; the top surface of the shotcrete is maintained ata 45-degree slope. (Same as bench gunning.)

Shooting(See gunning.)

ShotcreteMortar or concrete pneumatically projected at highvelocity onto a surface; also known as air-blown mortar,pneumatically applied mortar or concrete, sprayed mortar,or gunned concrete. (See also Dry-Mix Shotcrete,Pneumatic Feed, Positive Displacement Concrete Pump,and Wet-Mix Shotcrete.)

SloughingSubsidence of shotcrete, plaster, or the like, due generallyto excessive water in the mixture; also called sagging.

Water RingA device in the nozzle body of dry-mix shotcreteequipment through which water is added to the materials.

Wet-Mix ShotcreteShotcrete wherein all ingredients, including mixing water,are mixed before introduction into the delivery hose; itmay be pneumatically conveyed or moved bydisplacement. (See also Pneumatic Feed and PositiveDisplacement Concrete Pump.)

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EM 1110-2-200531 Jan 93

Appendix CShotcrete ApplicationsCorps of Engineers Projects

C-1

EM

1110-2-200531

Jan93

C-2

Applications

Tunnel Lining

Tunnel Lining

Spillway Ogee

Canal Lining

Navigation Lock Coating

Navigation Lock Rehabilitation

Tunnel Lining

Rock Slope Prot

Tunnel Lining

Rock Slope Prot

Tunnel Lining

Sloped Channel

Repair/Overlay

Dry-Mix

Type of Shotcrete

Dry-Mix w/Silica Fume

Wet-Mix

Wet-Mix and Wet-Mix with Steel Fibers

Wet-Mix with Glass Fibers and Polymer

Wet-Mix

Wet-Mix with Steel Fibers

Dry-Mix with Accelerator

Dry-Mix with Accelerator

Dry-Mix

Dry-Mix

Wet-Mix

Project Location District

Little Goose Dam Snake River, WA Walla Walla

Lower Monumental Dam Snake River, WA Walla Walla

Willow Creek Dam Heppner, OR Walla Walla

Mill Creek Lake Walla Walla, WA Walla Walla

Lower Monumental Dam Snake River, WA Walla Walla

Emsworth, Dashields Pittsburgh, PA Pittsburgh, PA Monongahela Lock No.3

Harlan Diversion Project Harlan, KY Nashville

New Melones Dam Stanislans River, CA Sacramento

New Melones Dam Stanislans River, CA Sacramento

Little Dell Dam Del Creek, Utah Sacramento

Little Dell Dam Del Creek, Utah Sacramento

Los Angeles River Channel Los Angeles River, CA Los Angeles

EM 1110-2-200531 Jan 93

Appendix DMixture Proportioning Sample Submittal

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EM 1110-2-200531 Jan 93

D-2

HARCON INCORPORATED P.O.BOX 2661 POCATELLO, ID, 83206-2661

SHOTCRETE MIX DESIGN (BY VOLUME) Mix I 1

------------------------------------------------------------------------------Project f DACW 68-9~-C-0002

LOWER MONUMENTAL PERMANENT JUVENILE FISH BYPASS FACILITIES

Shotcrete Producer: Connell Sand & Gravel, Inc., Connell, Wa. Shotcre~ Uses: Gallery Lining

W/C ratio <= 0.40, Entrained air = NA Cement from: South Dakot~ Cement

c.A.= 3/8" x #4 w/ ASTM C 33 combined gradation per 3B-6.3 Bulk S.G.: SSD = 2.81 Absorption= 2.2X Source = Connell Sand & Gravel

F.A.= Concrete Sand w/ ASTM C 33 combined gradation per 3B-6.3 Source = Connell Sand & Gravel Bulk S.G.: SSD = 2.706 Absorption= 3.2X F.M. =

COMPUTATION of 1 CY TRIAL MIX Ingredients Batch Weights

WATER @ W/C = 0.36 256 CEMENT T I-II LA 705 C.A. (3/8"x#4) 640 0.21 F.A. 2450 0.79 SILICA FUME 56 o.oa VOLUME

Revised 5/22/91 S.G. SSD

1.000 3.150 2.590 2.625 2.200

Volume

4.095 3.587 3.960

14.957 0.408

---------27.006

3.01

91-02---38-2.1----1

EM 1110-2-200531 Jan 93

TILBURY CEMENT COMPANY

DATE-06-04-91Connell Sand & Gravel

Sieve Size Percent Passing Specification

3/8" 100 100

#4 98 95-100

8 77 80-100

16 70 50-85

30 42 25-60

50 15 10-30

100 5 2-10

200 2

F M 2.83

Screen Size Percent PassingASTM

Specification

3/8" 100 85-100

#4 13 10-30

#8 4 0-10

#16 0 0-5

Screen Size80% Sand 20% 3/8"

Percent Passing Specification

1/2" 100 100

3/8" 100 90-100

#4 81 75-85

8 62 50-75

16 55 35-55

30 34 20-35

50 12 8-20

100 4 2-10

TESTED BY

D-3

EM 1110-2-200531 Jan 93

D-4

INTERMOUNTAIN MATERIALS TESTING, INC. 7446 Lemhi St., Boise, Idaho 83709 (208) 376-8203 1718 West A St., Pasco, Washington 99301 (509) 547-1121

Materials Engineering and Testing • REPORt TO:

PRO.JECTs

F~usett Mine Services P. 0. I'tox 9f·8 Osbourn, ID 83849

Lower Monument~! D~m

~mple ldentifico~~tion

Construction Inspection • DATEs FILE HUMllERJ SHEET I INVOICE I

Project. Consultation

6-e6-91 91-!53 2 of 6 T910i!79

On Mo~~y e9, 1991, your personnel deliver•d to our lo11boro11tory shot cr•t• cores. It was reported that the test po11nels were shot on Hay ee, 1991, by your opero~~tor, Rainville. The po~~n•ls were reportedly shot o11t horizontAl position, using mix H1 <7.~ bAg mix with 8~ silicA flume),

At yoc.cr r•qc.c•st:, w• p•rform.,d co111pr•••.tv• str•11gth t•sts in .u:cordo~~nc• with ASTM C4e. The test results Are AS follbws.

I••t Results Do~~te L•nath Compressive

Lo11b Humber Tested Age DiAmet•r Stre11gth PSI 911833 6-0:5-91 14 iL.ru! 4100

~.7!5

9·11834 6-0:5-91 14 4,88 4130 e.7:s

911838 6-19-91 e8 ~ 6770 e. ns

911839 6-19-91 ee 4.87:5 6180 e.7:5

EM 1110-2-200531 Jan 93

D-5

INTERMOUNTAIN MATERIALS TESTING, INC. 7448 Lemhi St., Boise, Idaho 83709 (208) 378-8203 1718 West A St., Pasco, Washington 99301 (1509) 1547-1121

Materials Engineering and Testing • REPORT TO: F~usett Mine Servi~es

P.O. 1\ox 9E.B Osbourn, ID 83849

PROJ'ECT: Lower Monument~l .D~m

S "'"' C!l e I den ti f1 ~., ti on

Construction Inspection • .DATE I FILE NUM~Eih SHEET• INVOICEs

Project Consultation

E.-eE.-91 91-:53 4 of 6

T910e79

On l'la1Y 29, 1991, your personnel delivered to our lo~~boro~~tory shot: crete cores. It w.,s reported th~t the test p.,nels wer• shot on M~y ee, 1991, by your oper.,t:or, E.,sl•y. The po~~n•ls were reportedly shot: .,t horizontal posit:Jon, using mix »1 <7.~ bo~~g mix with 8% sili~., flume).

At your request:, we performed ~ompressive strength t:est:s in "'~~ordo\n~• wit:h ASTN C42. The t:est: results Are As follows.

rest Results D111te Length Co111pressive

L.,b NunJber T•sted Ag• J>i.,lll•t:•r Str•ngth PSI 9118:54 E.-17-91 eE. 4.37:5 :5910

.:!.7:5

9118:5:5 6-17-91 i!6 4.E.2:S :S8E.O 2.7:5

9118:SE. 6-19-91 es ~ 6480 2.7:5

9118:57 6-19-91 28 ~ 6700 e.7:s

EM 1110-2-200531 Jan 93

D-6

INTERMOUNTAIN MATERIALS TESTING, INC. 7446 Lemhi St., Boise, Idaho 83709 (208) 376-8203 1718 West A St., Pasco, Waahlnaton 99301 (509) 547·1121

Materials Engineering and Testing • REPORT TO: F~usett Mine Services

P. 0. flo.~ 968 Osbourn, ID 83849

PRO.JECTs

S~mple IdentificAtion

Construction Inspection • DATE• FILE NUMI'ER1 SHEET• INVOICE I

Project Consultation

6-e6-91 91-::!3 6 or 6 T910e79

On MAy e9, 1991, your personnel delivered to our lAboratory shot crete cores. It was reported th~t the test pAnels were shot on HAy ee, 1991, by your operAtor, Cunningham. The panels were reportedly shot •b horizont~l position, using mix U1 <7.5 bag mix with 8~ silica flume>.

At your request, we performed compressive strength tests in accord~nce with ASTH C4e. The test results are as follows.

Iest B!!~l!l ts DAte bJmqth Compressive

L~b Number Tested Age Dianieter Strength PSI 911871 6-17-91 26 ~ ::S9eo

?• ?:S

911872 6-17-91 e6 6.1e::s ::!860 e.75

911873 6-19-91 ee 3.&75 6130 e.7::s

911874 6-19-91 ee 4.625 61eo e.75

Reviewed by

EM 1110-2-200531 Jan 93

D-7

To:

SOUTH DAKOTA CEMENT

Connell Sand & Gravel Inc.

P.O. Box 156

Connell, Vy. 99326

Rea D.A.CW68-9t-c-ooo2

Franklil\ Co. Lover Monumental

Permaaan~ Juvenile Fish

Bypass Facility

CERTIFICATION OF COMPLIANCEs

Thfs is to certffy that all Dakota Type t-It LA Portland Cement shipped to you meets or exceeijs the quality standards set forth by the American Society for Testing and Materials (ASTM C- 150- B9).

Questions concerning these specifications may be directed to this­office at the above number.

~~ Signature Quality Control Manager

30 January. 1991 Date

RECEIVED CONSTRUCTION DIV. WALLA W!nf:Af-DIST.

Slo=------t-P~_..;.----~·=~~-6_F_E_B_t_~_1 _____________ _

·91-02---3A-002----1

EM 1110-2-200531 Jan 93

D-8

OF COHPL~l~A~NC~b------~------------------------~ OTAH CEMENT

LBS. CAl~ I LBS. TV, SOUTH DAKOTA

CAR tt &N 441440 BN 4412:54

195700 ----- ----197000

CEMENT

DESTINATION ••••••• PASCO, WA

-----------------------------------------------------------------------~ TYPE: 1-Il LA BIN tt LADtt S191S

A.S.T.M. C-lS0-99 S~ECIFICATJDN LIMtT

DACOTAH C£11ENT

=••••••••••••••====s••••••••••••••••••••n••••••••••••••••••••••••••••••• CHEMICAL. TYPE I TYPE U ANALYSIS

------------------------------------------------------------------------Silicon dioxide. min. ~ (Si02) Aluminum ouida. ma», X CA120J) Farric oxide. max. X <F•203J Maonasium OKida. maK, X <HQO) Sulfur t1•1o:dda. m•:<. :~ CS03)

When CC3A) i& 9~ or less Less on 1on1ticn. max, X ln•olubla r•sidua, m~u, X Tric~lcium aluminate. mau, X <CZA) Alkalies. ma.x. X (.Jf) Cas Na eQ.) •~•u•••••••a•••a•a•••~••••••••••••••

F·HVSICAl.

-------------------------------------IHaine F1nenesos. CM2/K~) 1 min Autoclave axoanuion, max, X Gillmore initial set t1ma, m1n. Gillmore final sat time. ma~. Vlcat svttinQ t1ma.min,not lass than

maK,nct mer• th•n 3 Day Comorasslva Stran9th 1 p ••• l. 7 Dav Ccm~rassiva Strength, p.s.i. ~B Day CcmcreG~iva Streng~h, p.s.t. Air content of mcrtar.voium•, maK, ~ False set final canatratlon, min, (4)

6.00

a45 hs1S lSOO 2900 4000 12.0

!0

95 -0.02

2&SO 10100 4 • :so

145 2:10 ,,. 1 ~ 1500 Z185 2SOO 4753 4000 6920 12.0 S.7

so ---------------------------------------------~--------------------------(.Jf) Oction~l Recuirement• Thi~ will cer•tify that the above described shiDmant ct DACOTAH cement moats curr•nt ASTM C150-S9 and AASHTO MSS •pacifications. All teetino comcliea with the reoutremants by A.S.T.M. fo~ Portl~nd Cement. WE ARE NOT RESPONSIBLE FOR ANY ADDITIVES NOT STATED IN THE CERTIFICATE OF COMPLIANCE. . DATE Or- REPORT •••• (11/22/91 CHEI1I8T.. Cout•t f•attarson'"

C3S •••••• C4AI= •••••

48.16 10. 11

91-02---3A-002----2

EM 1110-2-200531 Jan 93

D-9

Mtl&tfr Builders Technologies

I IIIII ••••••

Master Builders, Inc. 1:1100 etw;rln !ou.~r• Clewland. Oftlo CC12a·~ PhoN 1111131•1100 '1altllN0-301

~ 12, 1991

certificate ot Qual.ity Mcstar auil.ders Paw sllica f\lme Mineru ~ ~ ~ scu:ce)

P.e: o:nps. ot ~ineenl Projects

m WH:K rr JoP.Y ~=

state ot Ohio ) a O:liJnty ~ takQ )

Before ma, a Notaey Public, in ard for the atortliatd stata and Q:~Unt:;r, pcaona.lly a~ Brien E. caine, tmo tefnil c1Ul.Y awom, deposu ard AYSJ

'!hat ha !a Manaqer, Chsmistry Laboratory for Mastar 81flder8, :tng,, Cl.cvel.an:i, Cbior ani

'Ihs.t Raw Silica Puma Mineral hbnixt:urG (West ~ SCQ:ca) iJI Muter BUilders dry ~ctad silica tumll mineral adrdJd:Ura tor ~in; the p~ies of hat't!enod concrete, ~ially ~ and ~.uityJ an:1

'lhat Raw Silica .nmwa Minclral. ~ (wcct oout SOUZ'oll) ..ca tha tolle»~ing Mastar EW.lders quality UIR.2J:anl» ~ cri~·iaa

s~te of Ohio M,y O:zrm\ission Expires Febxuary 7, 1996

(~rded 1n Lake ~ty)

Oca. !5325

8!5.0 l.S 3.0 cs.o

10.0* Not 'l'e.st8cl Not. '1'estC