ACI 506.2-95
Specification for Shotcrete (ACI 506.2-95) Reported by ACI Committee 506
Steven H. Gebler Chairman
Lars Balck, Jr. Secretary
Jon B. Ardahl
Bruce K. Langson
Ernest K. Schrader
Seymour A. Bortz Paul D. Carter
Albert Litvin Kristian Loevlie
Vern Schultheis Raymond J. Schutz
Gary L. Chynoweth
Dudley R. Morgan
Philip T. Seabrook
John R. Fichter
Dirk E. Nemegeer
W. L. Snow, Sr.
I. Leon Glassgold
H. Celik Ozyildirim
Curt E. Straub
Jill E. Glassgold
Harvey W. Parker
Lawrence J. Totten
Warren L. Harrison
Dale A. Pearcey
Gary L. Vondran
Charles H. Henager Merlyn Isaak
John E. Perry, Jr. Vankataswamy Ramakrishnan
R. Curtis White, Jr. J. Wickman Zimmerman
Richard A. Kaden
Thomas J. Reading
This specification contains the construction requirements for the application of shotcrete. Both wet-mix and dry-mix shotcrete are specified, and the minimum standards for testing, materials, and execution are provided.
2.2—Aggregate 2.3—Reinforcement 2.4—Water 2.5—Admixtures 2.6—Curing materials 2.7—Proportioning 2.8—Fiber reinforced shotcrete 2.9—Prebagged materials 2.10—Delivery, storage, and handling
Keywords: dry-mix shotcrete, fiber reinforced shotcrete, nozzleman, shooting, shotcrete, wet-mix shotcrete
CONTENTS Foreword, p. 506.2-2 Preface to specification checklist, p. 506.2-2 Mandatory requirements checklist, p. 506.2-2
Section 3—Execution, p. 506.2-7 3.1—Examination 3.2—Batching and mixing 3.3—Surface preparation 3.4—Joints 3.5—Alignment control 3.6—Application 3.7—Finishing 3.8—Curing 3.9—Hot weather shotcreting 3.10—Cold weather shotcreting 3.11—Protection 3.12—Tolerances
Optional requirements checklist, p. 506.2-2 Submittals checklist, p. 506.2-3 Section 1—General, p. 506.2-4 1.1—Scope 1.2—Definitions 1.3—Reference organizations 1.4—Reference standards 1.5—Submittals 1.6—Quality assurance 1.7—Shotcrete core grades 1.8—Evaluation of in-place shotcrete 1.9—Acceptance
Section 2—Materials, p. 506.2-7 2.1—Cement
ACI 506.2-95 supersedes ACI 506.2-90 and became effective October 1, 1995. Copyright © 1995, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.
506.2-1
506.2-2
ACI STANDARD
FOREWORD F1. This foreword is included for explanatory purposes only; it does not form a part of Standard Specification ACI 506.2. F2. Standard Specification ACI 506.2 is a reference standard which the Architect/Engineer may cite in the project specifications for any project, together with supplementary requirements for the specific project. F3. Each technical section of Standard Specification ACI 506.2 is written in the three-part section format of the Construction Specification Institute, as adapted by ACI and modified to ACI requirements. The language is generally imperative and terse. F4. Checklists do not form a part of Standard Specification ACI 506.2. Checklists are to assist the Architect/Engineer in properly choosing and specifying any necessary requirements for the project specifications.
PREFACE TO SPECIFICATIONS CHECKLIST P1. Standard Specification ACI 506.2 is intended to be used by reference or incorporation in its entirety in the Project Specifications. Individual sections, articles, or paragraphs shall not be copied into the Project Specifications, since taking them out of context may change their meaning. P2. If sections or parts of Standard Specification ACI 506.2 are edited into Project Specifications or any other document, they shall not be referred to as ACI Standards, since the Standard Specification has been altered.
P3. Building codes set minimum requirements necessary to protect the public. These Standard Specifications may stipulate requirements more restrictive than the minimum. Adjustments to the needs of a particular project shall be made by the Architect/Engineer by reviewing each of the items in the Specifications Checklist and then including the Architect/Engineer's decision on each item as a mandatory requirement in the Project Specifications. P4. These mandatory requirements designate the specific qualities, procedures, materials, and performance criteria for which alternatives are permitted or for which provisions were not made in the Standard Specifications. Exceptions to the Standard Specifications shall be made in the Project Specifications, if required. P5. A statement such as the following will serve to make Standard Specifications ACI 506.2 a part of the Project Specifications.
“Work on (Project Title) shall conform to all the requirements of ACI 506.2 Standard Specification for Shotcrete, published by the American Concrete Institute, Detroit, Michigan, except as modified by the requirements of these Contract Documents.” P6. The Standard Specifications Checklist identifies Architect/Engineer choices and alternatives. The checklists identify the sections, parts, and articles of the Standard Specifications and the action required by the Architect/Engineer. Architect/Engineer.
MANDATORY MANDATORY REQUIREMENTS CHECKLIST
Section/Part/Article 2.7—Proportioning 3.3—Surface preparation
3.12 3.12— —Tol Toleran erance ce
Notes to the Architect/Engineer Specify design strength of shotcrete. Specify if other properties or a particular mix proportion is required. Specify results. Sometimes special surface preparation is required to assure bond. A rough surface provides the best bond. Specifying a reveal is helpful. It may be difficult to measure bond strength. It also may be necessary to remove existing concrete or shotcrete to allow for proper reinforcement encasement. In some cases, bond to an existing surface may not be needed. If bond is not required, specify what result is required. Coating material used on shotcrete forms must be used with caution. Shooting against forms removes surface materials and mixes it with the shotcrete that may alter the shotcrete properties. Form coating materials may also interfere with the bond of subsequent layer of shotcrete. Specify if special surface preparation between layers of shotcrete is required. Preparation can be accomplished by scraping, brooming, high pressure water blasting or sand blasting. Speci peciffy to tolera leran nce base based d on on fu funct nction ion and and app appear earance ance.. Sho Shotc tcrrete ete is is typ typic ical allly no not hel held d to to the the same same tolera leran nce as cast cast--ininplace concrete. Sometimes no tolerances are specified, while sometimes shotcrete tolerances are increased by a factor of 2 times over the tolerances provided in ACI 117.
OPTIONAL REQUIREMENTS CHECKLIST
Section/Part/Article 1.4— 1.4—Re Refe fere renc ncee stan standa dard rdss
1.5— 1.5—Su Subm bmit itta talls
Notes to the Architect/Engineer The The foll follow owin ing g refe refere renc nces es are are pro provi vide ded d as gui guide des. s. The They y are are not not lega legall docu docume ment nts. s. The They y cann cannot ot be be refe refere renc nced ed in in the the shotcrete specification. The references, however, provide excellent information, and can prove helpful in the design, the construction, and the inspection of shotcrete work. ACI ACI 506. 506.4R 4R Evalua Evaluatio tion n of of In-P In-Plac lacee Shot Shotcre crete te ACI ACI 506.3R 506.3R Guide Guide to Cert Certifi ificat cation ion of of Shotcr Shotcrete ete Nozz Nozzlem leman an ACI 506R Guide to Shotcrete ACI 506.1R 506.1R State-ofState-of-thethe-Art Art Report Report on Fiber Reinforced Reinforced Shotcrete Shotcrete Spec Specif ify y if if ot other her sub submi mitt ttal alss ar are nee neede ded d su such as mix mix pro propo port rtio ions ns and and res resu ults lts of of pre preco cons nsttruct ructiion tests ests when hen sp speci ecified fied..
SPECIFICATION FOR SHOTCRETE
506.2-3
OPTIONAL REQUIREMENTS CHECKLIST, continued OPTIONAL REQUIREMENTS CHECKLIST
Section/Part/Article 1.6—Quality assurance
Notes to the Architect/Engineer Specify whether preconstruction testing is required. Specify compatibility for admixtures for wet-mix shotcrete. Specify type and frequency of additional tests if needed. Preconstruction testing is not always justified or practical. Examples are: noncritical applications or small jobs, temporary construction, when job conditions do not allow enough time, and when the contractor has recently completed similar acceptable work with similar materials, personnel, and equipment. The cost of testing should be weighed against potential benefits. If the contractor can show satisfactory results on previous jobs with the same materials, personnel and equipment, the engineer should give consideration to eliminating the requirement of preconstruction testing. Flexural strength in accordance with ASTM C 78 and toughness in accordance with ASTM C 1018 in addition to compression tests are usually required as prequalification of fiber reinforced shotcrete. When prequalification testing is required, a ratio of compressive to flexural strength is to be established for quality assurance purposes, then compressive
design strength would govern as acceptance. Specify the frequency of testing and acceptance criteria. Concrete design strength is based on cast concrete cylinders. Shotcrete design strength, however, is based on cores or sawed cubes taken from a sample panel. Core sample strength, however, is expected to be 0.85 of cast c ylinder strength (ACI 318 paragraph 5.6) since core samples are disturbed due to the coring or cutting process. Quality shotcrete is highly dependent on the contractor and the workmanship of the nozzleman. The nozzleman should demonstrate his ability and knowledge or have proven his ability through nozzleman testing. At the present time, Nozzleman Certification ACI 506.3R is a report (not a standard) and may not be referenced in the ACI Shotcrete Specification. The specifying authority, however, can specify nozzleman certification in accordance with 506.3R or other suitable requirement. Language, however, must be mandatory. 1.7—Sh 1.7—Shotc otcret retee core core grades grades Specif Specify y core core grad gradee of of shot shotcre crete te requ require ired. d. Grade Grade 1 cores cores are optimu optimum, m, howe however ver,, Grad Gradee 1 cores cores cann cannot ot be consis consisten tently tly shot. Grade 2 cores are used for most structural members. 1.8—Eval 1.8—Evaluatio uation n of in-place in-place shotcrete shotcrete Specify Specify acceptance/re acceptance/rejecti jection on criteria. criteria. 2.1—Cement Specify if if ot other ty type of of ce cement is is al allowa bl ble If If re require d, d, sp specify bl blended hy hydraulic ce ce me me nt nt in in ac ac co corda nc nce wi with AS ASTM C 595. Base se lection of cement type on sulfate exposure conditions or other conditions. 2.2— 2.2—A Aggre ggreg gate ate Speci pecify fy if oth other er grad gradiing, ng, ty type or or tes testts are are req require uired. d. Spec Speciify cri criteria eria for acce accept ptan ance ce.. Oth Other er grad gradiings ngs pr propos oposed ed by the contractor may be acceptable if the contractor can demonstrate satisfactory performance under similar conditions of use. 2.3— 2.3—Re Rein info forc rcem emen entt Spec Specif ify y typ type, e, size size,, con confi figu gura rati tion on,, min minim imum um cont conten ent, t, test testss req requi uire red, d, or requ requir ired ed test testin ing g fre frequ quen ency cy and and acce accept ptan ance ce criteria. 2.5— 2.5—A Admi dmixtu xtures res A co concre ncrette mi mix doe doesn sn't 't beco ecome sho shotcre tcrette unt untiil it it is is pl placed aced at a hig high h vel velo ocit city. Measu easuri ring ng air air con conte ten nt at at th the pu pump hopper, measures concrete air content not shotcrete air content. Shotcrete air content can be measured by taking samples from in-place material. If air content is to be tested, specify where the sample is to be taken. Wet-mix shotcrete exposed to moderate or severe freeze/thaw conditions should have air entrainment in the concrete prior to shooting. Six to seven percent (6 - 7 percent) air content in the concrete is required prior to shooting. Entrained air is lost during shotcreting. Obtaining greater than 4 percent entrained air in in-place wet-mix is difficult. If a greater percent is required, test practicality. Specifying air entrainment for dry-mix is not recommended. Specify limits and types of other acceptable admixtures. Specify dosage if important. Calcium chloride is not recommended in reinforced shotcrete structures. Tables in ACI 201 or ACI 318 provide limits. If specified, it shall conform to ASTM D 98. Specify if other admixtures are allowable. 2.8—Fibe r ACI 506.1R—“State-of-the-Art Report on Fiber Reinforc ed ed Shotcrete ” provides guidance for fiber shotc re rete. 3.3. 3.3.3— 3—Su Surf rfac acee pre prepa para rati tion on It is reco recomm mmen ende ded d tha thatt ste steel el surf surfac aces es shou should ld comp comply ly with with SSPC SSPC-S -SP6 P6 3.3. 3.3.3. 3.2. 2. 3.3.5—Forms High ve velocity ai air tr transporting th the sh shotcre te te mi mix, if if no not al allowed to to es escape, ma may cr cre at ate vo voids at at fo form co corners. 3.4.1—Joints Specify square joints for construction joints subject to compression loads. 3.5— 3.5—Al Alig ignm nmen entt cont contro roll For For lon long g span spanss (ove (overr 30 ft), ft), dev devic ices es tha thatt per permi mitt tigh tighte teni ning ng of of grou ground nd wir wires es,, such such as as spri spring ngss or turn turnbu buck ckle less can can be be used used.. 3.6. 3.6.1— 1—Ap Appl plic icat atio ion n Do not not pla place ce subs subseq eque uent nt lift liftss unt until il the the pre previ viou ouss lif liftt has has hard harden ened ed enou enough gh to supp suppor ortt the the new new sho shotc tcre rete te.. Ver Verti tica call wal walls ls should be gunned from the bottom up unless it can be demonstrated that another method will work successfully. 3.6.2—Encasement of reinforcement reinforcement Voids behind behind bars are not not easily evident evident by inspection. inspection. Limiting Limiting the maximum size reinforcement reinforcement bar to to a No. 5 bar increases the likelihood of complete encasement, especially with limited experienced crews. Encasing larger bars requires great care, along with high impact velocity and plasticity. Close inspection is also needed. See “Guide to Shotcrete,” 506R-85 Section 5.4.1.2. 3.7— 3.7—Fi Fin nish ishing ing Speci peciffy ty type of fini inish. sh. If If ot other her tha than n a gun fi finish nish is req requ uired ired,, spe speci cify fy finis inish h ty types pes suc such h as as ro rod, broom room,, woo wood d fl float oat, rub rubbe berr float, or steel trowel. Disturbance of the shotcrete surface by finishing may reduce the durability of the surface. Material to correct small flaws may be added if the material is fresh and properly proportioned. 3.8—Curing Caution must be exercised when using curing c om ompounds. Curing compounds can interfere with the bond of subsequent layers of shotcrete. If curing compounds are used and additional layers of shotcrete are to be applied, the curing material must be removed by either water blasting or sand blasting. Steam curing is acceptable provided the steam temperature is less than 150 F. 3.10—Cold weather ACI 306.1 standard specification should be reviewed.
SUBMITTALS CHECKLIST
Section/Part/Article 1.5—Submittals
Notes to the Architect/Engineer Proposed shotcrete mix. Test panel results if required.
506.2-4
ACI STANDARD
SECTION 1—GENERAL 1.1—Scope This Standard Specification describes the requirements for materials, proportioning, and application of shotcrete.
1.2—Definitions Accepted —Accepted —Accepted by or acceptable to the Architect/Engineer. Architect/Engineer —The —The architect, engineer, architectural firm, engineering firm or architectural and engineering firm issuing project drawings and specifications or administering the work under the Contract Documents. Contract Documents—Documents covering the required work and including the project drawings and project specifications. Contractor —The —The person, firm, or corporation that the owner enters into an agreement with for construction of the work. Core grade—Quality ranking of a shotcrete core. Dry-mix shotcrete —Shotcrete in which most of the water is added at the nozzle. Fiber-reinforced shotcrete (FRS) —Shotcrete mixed with discrete discontinuous fibers commonly made of steel, plastic, or alkali resistant (AR) glass. Finish coat —Final —Final thin coat of shotcrete preparatory to hand finishing. Flash coat —Thin —Thin shotcrete coat applied from a distance greater than normal for use as a final coat or for finishing. Ground wire—Wire used to establish line and grade for shotcrete work. Gun—Dry-mix shotcrete delivery equipment. Gun finish—Undisturbed final layer of shotcrete as applied from nozzle without hand finishing; also known as natural or nozzle finish. Nozzle—Attachment at end of delivery hose from where shotcrete is projected. Nozzleman—Worker on shotcrete crew who manipulates the nozzle, controls consistency of dry-mix shotcrete, and controls final disposition of the material. Overspray—Shotcrete material deposited away from the intended receiving surface by air blast. Owner —The —The corporation, association, partnership, individual, or public body or authority with whom the contractor enters into agreement and for whom the work is provided. —Shotcrete material that ricochets off the Rebound —Shotcrete receiving surface. Sand/rock pocket —A —A porous zone in the shotcrete containing aggregate with reduced mortar content. Shooting—Act of applying shotcrete. Shotcrete—Mortar or concrete pneumatically projected onto a surface at high velocity. Sloughing—Subsidence of shotcrete, due generally to excessive water in mixture or to vibration of continuous reinforcement or formwork. —Submitted to the Architect/Engineer for Submitted —Submitted review. Wet-mix shotcrete —Shotcrete in which plastic concrete with cement, aggregate, and water are first mixed together before introduction into the delivery hose.
—The entire construction or separately identifiable Work —The parts that are required to be furnished under the Contract Documents. Work is the result of performing services, furnishing labor, and providing and incorporating materials and equipment into the construction, all as required by the Contract Documents.
1.3—Reference organizations American Concrete Institute P.O. Box 9094 Farmington Hills, Mich. 48333-9094 ASTM International 100 Barr Harbor Dr. West Conshohocken, Pa. 19428-2959 Steel Structures Painting Council 4400 Fifth Avenue Pittsburgh, Pa. 15213
1.4—Reference standards The following Reference Standards are referred to in this specification and declared to be a part of this Standard Specification: 1.4.1 ACI 1.4.1 ACI Standards ACI 301-89 301-89 Specificat Specifications ions for Structura Structurall Concrete Concrete for Buildings, paragraph 5.7.1 and Chapter 9 1.4.2 ASTM 1.4.2 ASTM Standards A 185 Specif Specifica icatio tions ns for for Wire Wire Fabric Fabric,, Plain, Plain, Welded Welded Steel for Concrete Reinforcement A 615 Specif Specifica icatio tions ns for Bars, Bars, Defor Deformed med and and Plain, Plain, Billet-Steel, for Concrete Reinforcement A 820 Specif Specifica icatio tions ns for for Steel Steel Fiber Fiberss for Fiber Fiber Rein Rein-forced Concrete C 31 Prac Practi tice ce for for Mak Makin ing g and and Curi Curing ng Conc Concre rete te Test Test Specimens in the Field C 33 Spec Specif ific icat atio ion n for for Conc Concre rete te Aggr Aggreg egat ates es C 42 Test Test Meth Method odss for for Obt Obtai aini ning ng and and Test Testin ing g Dril Drille led d Cores and Sawed Beams of Concrete C 94 Spec Specif ific icat atio ion n for for Read Readyy-Mi Mixe xed d Conc Concre rete te C 109 109 Test Test Metho Method d for for Comp Compre ress ssiv ivee Stre Streng ngth th of Hydraulic Cement Mortars C 150 150 Spec Specif ific icat atio ion n for for Port Portla land nd Ceme Cement nt C 171 Specif Specifica icatio tion n for Sheet Sheet Mate Materia rials ls for Curi Curing ng Concrete C 309 Specif Specifica icatio tion n for Liquid Liquid Membrane Membrane-Fo -Formi rming ng Compounds for Curing Concrete C 330 Specif Specifica icatio tion n for Lightwe Lightweigh ightt Aggrega Aggregates tes for for Structural Concrete C 595 595 Specif Specifica icatio tion n for for Blende Blended d Hydr Hydraul aulic ic Cement Cementss C 618 Specif Specifica icatio tion n for for Fly Fly Ash Ash and and Raw Raw or Calcin Calcined ed Natural Pozzolan for use as a Mineral Admixture in Portland Cement Concrete C 642 Test Test Metho Method d for for Spec Specifi ificc Gravi Gravity, ty, Absorp Absorptio tion, n, and and Voids in Hardened Concrete C 685 Specif Specifica icatio tion n for Concre Concrete te made made by by Volume Volumetri tricc Batching and Continuous Mixing C 989 Specif Specifica icatio tion n for Ground Ground Granula Granulated ted BlastBlastFurnace Slag for use in Concrete and Mortars
SPECIFICATION FOR SHOTCRETE
C 1116
Specificat Specification ion for Fiber-Rein Fiber-Reinforce forced d Concrete Concrete and Shotcrete C 1140 1140 Standard Standard Practice Practice for Preparing Preparing and Testing Testing SpecSpecimens from Shotcrete Test Panels C 1141 Standard Standard Specifi Specificatio cation n for Admixt Admixtures ures for for ShotShotcrete 1.4.3 SSPC Standards SP6 SP6 Surf Surfac acee Prep Prepar arat atio ion n Spec Specif ific icat atio ion n No. No. 6, Comm Commer er-cial Blast Cleaning
506.2-5
1.6.2.2 Test specimens from in-place shotcrete in compliance with ASTM C 42. 1.6.2.3 Grade cores that include reinforcement in accordance with Section 1.7—Shotcrete core grades. 1.6.2.4 The mean compressive strength of a set of three cores shall equal or exceed 0.85 f c with no individual core less than 0.75 f c . The mean of a set of three cubes shall equal or exceed f c with no individual cube less than 0.88 f c . ′
′
′
′
1.7—Shotcrete core grades 1.5—Submittals Submit proposed mix characteristics including: • Prop Propor orti tion onss by weig weight htss or or volu volume mess • Strength • Wate Waterr-ce ceme ment ntit itio ious us mate materi rial alss rat ratio io • Aggr Aggreg egat atee sou sourc rcee and and grad gradin ing g • Cement ty type an and br brand • Wate Waterr sour source ce if othe otherr than than pota potabl blee • Proportions • Adm Admixtur xtures es data data she sheets ets • Test results Submit preconstruction test panel results when required.
1.6—Quality assurance 1.6.1 Preconstruction testing 1.6.1.1 Prepare preconstruction test panels for examination by Architect/Engineer prior to job shotcrete placement. Preparation and testing shall comply with ASTM C 1140. 1.6.1.2 Produce test panels for each proposed mix proportion, each anticipated shooting orientation, and each proposed nozzleman. Mixes shall meet requirements of Section 2.7—Proportioning. In half of the test panels provide reinforcement of the same size and spacing required for the work. Obtain six test specimens from each panel, three nonreinforced specimens and three with reinforcing steel. 1.6.1.3 Test the nonreinforced specimens for compliance with the specified physical properties in accordance with ASTM C 42. 1.6.1.4 Visually grade the reinforced specimens for compliance with specified core grade (Section 1.7—Shotcrete core grades). 1.6.1.5 Test admixtures for compatibility with cement in accordance with ASTM C 1141. 1.6.1.6 Unless otherwise specified, only nozzlemen with a test panel mean core grade less than or equal to 2.5 (Section 1.7) shall be allowed to place job shotcrete. When the prequalification test panel is rejected, a second panel may be shot. When the nozzleman's second mean core grade is greater than 2.5, the nozzleman shall not be permitted to shoot on the project. 1.6.2 Construction testing 1.6.2.1 Produce a material test panel for each mix and each work day or every 50 cubic yards placed, whichever is less. Test panel shall be kept moist and at 70 F ± 10 F until moved to test laboratory. Obtain test specimens either from job site material test panel or from in-place shotcrete. Test specimens from test panels in compliance with ASTM C 1140.
1.7.1 Grade 1: Shotcrete specimens are solid; there are no laminations, sandy areas or voids. Small air voids with a maximum diameter of 1/8 in. and maximum length of 1/4 in. are normal and acceptable. Sand pockets, or voids behind continuous reinforcing steel are unacceptable. The surface against the form or bond plane shall be sound, without a sandy texture or voids. 1.7.2 Grade 2: Shotcrete specimens shall have no more than two laminations or sandy areas with dimensions not to exceed 1/8 in. thick by 1 in. long. The height, width and depth of voids shall not exceed 3/8 in. Porous areas behind reinforcing steel shall not exceed 1/2 in. in any direction except along the length of the reinforcing steel. The surface against the form or bond plane shall be sound, without a sandy texture or voids. 1.7.3 Grade 3: Shotcrete specimens shall have no more than two laminations or sandy areas with dimensions exceeding 3/16 in. thick by 1-1/4 in. long, or one major void, sand pocket, or lamination containing loosely bonded sand not to exceed 5/8 in. thick and 1-1/4 in. in width. The surface against the form or bond plane may be sandy with voids containing overspray to a depth of 1/16 in. 1.7.4 Grade 4 core: The core shall meet in general the requirements of Grade 3 cores, but may have two major
Grade 1
506.2-6
ACI STANDARD
Grade 2
Grade 3
Grade 4
1.7.5 Grade 5 core: A core that does not meet the criteria of core grades 1 through 4, by being of poorer quality, shall be classified as Grade 5. 1.7.6 Determination of grade shall be by computing the mean of a minimum of three test specimens. 1.7.7 A mean grade of 2.5 or less is acceptable unless otherwise specified. Individual shotcrete cores with a grade greater than 3 are unacceptable. 1.7.8 The above core grades are based on cores with a surface area of 50 in. 2 For cores with greater or lesser area than 50 in.2, adjust allowable flaws relative to 50 in. 2
1.8—Evaluation of in-place shotcrete Remove and replace shotcrete that is delaminated, exhibits laminations, voids, or sand pockets exceeding the limits for the specified grade or shotcrete. Remove and replace shotcrete that does not comply with the specified material properties. Repair core holes in accordance with Chapter 9 of ACI 301. Do not fill core holes by shooting.
1.9—Acceptance
Grade 5
flaws such as described for Grade 3 or may have one flaw with a maximum dimension of 1 in. (25 mm) perpendicular to the face of the core with a maximum width of 1-1/2 in. The end of the core that w as shot against the form may be sandy and with voids containing overspray to a depth of 1/8 in.
1.9.1 Shotcrete work that meets applicable requirements will be accepted. 1.9.2 Shotcrete work that has previously failed to meet one or more requirements, but which has been repaired to bring it into compliance, will be accepted. 1.9.3 Shotcrete work that fails to meet one or more requirements and which cannot be brought into compliance may be accepted or rejected. Modifications may be required to assure that remaining work complies with the requirements.
SPECIFICATION FOR SHOTCRETE
SECTION 2—MATERIALS 2.1—Cement
Table 2.7—Total air content for frost-resistant concrete*
Portland cement: ASTM C 150. Type I
2.2—Aggregate Normal weight aggregate: ASTM C 33. Aggregate not meeting ASTM C 33 may be used provided preconstruction tests demonstrate the shotcrete can meet specified requirements. Lightweight aggregate: ASTM C 330
2.3—Reinforcement Deformed steel reinforcement: ASTM A 615 Welded wire fabric: ASTM A 185 Steel fibers: ASTM A 820 and C 1116 Glass fibers: ASTM C 1116 Synthetic fibers: ASTM C 1116
2.4—Water Clean and potable. Mixing water for shotcrete shall meet requirements of ASTM C 94. Water shall be free of elements that cause stains when used on architectural finishes.
2.5—Admixtures Water-reducing: ASTM C 1141 Retarding: ASTM C 1141 Accelerating: ASTM C 1141 Air-entraining: ASTM C 1141 Fly ash and natural pozzolans: ASTM C 618 Ground granulated blast-furnace slag: ASTM C 989 Silica fume: ASTM C 1240
2.6—Curing materials Curing materials that cause stains on architectural finishes shall not be used. Sheet materials: ASTM C 171 Curing compounds: ASTM C 309, apply twice the coverage (double the application rate) recommended by manufacturers.
2.7—Proportioning Select shotcrete proportions to produce the specified material properties. Shotcrete mix proportions using normal weight aggregate shall produce the following 28-day material property: f c : ASTMC 42; ASTM C1140 Air content: ASTM C 173 or C 231 ′
2.8—Fiber-reinforced 2.8—Fiber-reinforced shotcrete ASTM C 1116
2.9—Prebagged materials Are allowable with predampening.
2.10—Delivery, 2.10—Delivery, storage, and handling Deliver, store, and handle materials to prevent contamination, segregation, corrosion or damage. Store liquid admixtures in order to prevent evaporation and freezing.
506.2-7
Nominal maximum aggregate size†
Total Total air content, percent ‡
Less than 3/8 in.
7
Greater than 3/8 in.
6
*
Based on samples obtained from the concrete truck. See ASTM C 33 for tolerances for various nominal maximum size designations. ‡ A tolerance of 11 / 2 percent shall be allowed. †
SECTION 3—EXECUTION 3.1—Examination • Verify Verify that that surfaces surfaces are accept acceptable able and are are ready ready to receive work. • Verify Verify that forms forms are to to line and grade, grade, braced braced agains againstt vibration, and constructed to permit escape of air and rebound. • Verify Verify that placement placement and and clearanc clearancee around around reinforc reinforceement permits complete encasement. • Verify Verify that that surface surfacess to receive receive shotcr shotcrete ete have have been been properly prepared according to the Contract Documents.
3.2—Batching and mixing Weight batching shall comply with the accuracy specified in ASTM C 94. Volume batching shall comply with the accuracy specified in ASTM C 685. Volume batching shall be verified once a week by a weight batching check. Use batching and mixing equipment capable of proportioning and mixing the required materials. Shoot dry-mix shotcrete material within 45 min after batching or predampening. This requirement does not include dry, prebagged material unless prebagged material is predampened. Shoot wet-mix shotcrete material within 90 min after batching.
3.3—Surface preparation 3.3.1 Earth—Prepare surfaces to line and grade. Do not apply shotcrete to frozen surface. Dampen surface immediately prior to shooting. 3.3.2 Concrete, masonry, and shotcrete—When bonding is required, remove all deteriorated, loose unsound material or contaminants that may inhibit bonding. Chip areas to be repaired to remove offsets causing abrupt changes in thickness. Taper edges to eliminate square shoulders at the perimeter of a cavity. Surface shall be saturated surface dry immediately prior to shooting. —The surface shall be free 3.3.3 Structural/reinforcement —The of deleterious materials that inhibit bonding. For new construction, reinforcement laps shall be separated with a clearance of at least three times the diameter of largest aggregate. Reinforcement shall be secured to prevent movement. —Remove loose material, mud or other foreign 3.3.4 Rock 3.3.4 Rock —Remove material that will prevent bonding. Clean surface. Prewet surface immediately prior to shooting. 3.3.5 Forms—Use form-release coating material on removable forms. Secure forms to minimize the effects of
506.2-8
ACI STANDARD
vibration. Construct forms to allow escape of placement air and rebound.
Broom or roughen the surface of freshly placed shotcrete after shotcrete has reached initial set when subsequent layers are to be applied.
3.4—Joints 3.4.1 Construction joints —Taper construction joints at a 1 to 1 slope where joint is not subject to compression loads. Surface preparation of joints shall comply with Section 3.3.2. Continue reinforcement through construction joint. 3.4.2 Control joints —Place as shown on drawings. Discontinue reinforcement at control joints.
3.5—Alignment control Install taut ground wires or other means to establish thickness and plane of required surface. Install taut ground wires or other means at corners or offsets not established by forms.
3.6—Application 3.6.1 Placement techniques —Provide a platform that permits nozzleman unobstructed access to the receiving surface. Place shotcrete first in corners, recesses, and other areas where rebound or overspray cannot escape easily. Remove rebound and overspray from previously prepared surfaces prior to shotcrete placement. Place shotcrete with nozzle held approximately perpendicular to the receiving surface. In corners, direct nozzle at approximately 45 deg angle or bisect the corner angle. Apply shotcrete so sags or sloughing do not occur. Discontinue shooting or shield the nozzle stream if wind causes separation of ingredients during shooting. Do not reuse rebound or overspray. Remove laitance from shotcrete surfaces to receive additional shotcrete layers. Surface preparation after final set shall comply with Section 3.3.2. Do not apply shotcrete on surfaces with standing water or running water. Remove hardened overspray and rebound from adjacent surfaces, including exposed reinforcement. 3.6.2 Encasement of reinforcement —Place shotcrete to completely encase reinforcing steel. Encase reinforcement by shooting with sufficient velocity and plasticity so material flows around and behind the reinforcement. Front face of reinforcement shall remain clean during encasement. Place shotcrete to provide the cover over reinforcement required by ACI 301. Minimum slump of wet-mix shotcrete is 1 in.
3.7—Finishing Gun finish or as specified.
3.8—Curing Immediately after finishing, cure shotcrete continuously by maintaining in a moist condition for seven days or until specified strength is attained or until succeeding shotcrete layers are placed. Cure by one of the following methods: • Pond Pondin ing g or or con conti tinu nuou ouss spr sprin inkl klin ing g • Coveri Covering ng with with an an absor absorpti ptive ve mat mat or or sand sand that that is kept kept continuously wet • Cove Coveri ring ng with with impe imperv rvio ious us shee sheett mate materi rial al • Curing co compounds Natural curing shall be permitted if ambient relative humidity is maintained above 95 percent.
3.9—Hot weather shotcreting Do not place shotcrete when material temperature is above 90 F for wet mix; 100 F for dry mix. Lower temperature of reinforcement and receiving surfaces below 100 F prior to shooting.
3.10—Cold weather shotcreting Shooting may proceed when ambient temperature is 40 F and rising. 50 F for latex-modified shotcrete. Shooting shall discontinue when ambient temperature is 40 F and falling unless protective measures are taken to protect shotcrete. Shotcrete material temperature, when shot, shall not be less than 50 F or more than 90 F. Shotcrete shall not be placed against frozen surfaces. Applicable procedures used for cold weather concreting may be used for cold weather shotcreting.
3.11—Protection Protect surfaces not intended for shotcrete placement against deposit of rebound and overspray or impact from nozzle stream. Remove rebound and hardened overspray from final shotcrete surfaces and from areas not intended for shotcrete placement.
3.12—Tolerances Tolerances of shotcrete shall comply as specified.
ACI 506.2-95 was submitted to letter ballot of the committee and approved in accordance with ACI standardization procedures.
