506.2-95 Specification for Shotcrete

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
W. L. Snow, Sr.
John R. Fichter
Dirk E. Nemegeer
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
Richard A. Kaden
John E. Perry, Jr.
Vankataswamy Ramakrishnan
R. Curtis White, Jr.
J. Wickman Zimmerman
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.
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
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. 506.2-6
2.1—Cement
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
Section 3—Execution, p. 506.2-6
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
ACI 506.2-95 supercedes 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
3.9—Hot weather shotcreting
3.10—Cold water shotcreting
3.11—Protection
3.12—Tolerances
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.
Section/Part/Article
2.7—Proportioning
3.3—Surface preparation
3.12—Tolerance
Section/Part/Article
1.4—Reference standards
1.5—Submittals
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.
shall conform to all the
“Work on
(Project Title)
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.
MANDATORY REQUIREMENTS CHECKLIST
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.
Specify tolerance based on function and appearance. Shotcrete is typically not held to the same tolerance as cast-inplace concrete. Somtimes 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
Notes to the Architect/Engineer
The following references are provided as guides. They are not legal documents. They cannot be referenced in 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 506.4R
Evaluation of In-Place Shotcrete
ACI 506.3R
Guide to Certification of Shotcrete Nozzleman
ACI 506R
Guide to Shotcrete
ACI 506.1RState-of-the-Art Report on Fiber Reinforced Shotcrete
Specify if other submittals are needed such as mix proportions and results of preconstruction tests when specified.
SPECIFICATION FOR SHOTCRETE
506.2-3
OPTIONAL REQUIREMENTS CHECKLIST, continued
Section/Part/Article
Notes to the Architect/Engineer
1.6—Quality assurance
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 cylinder 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—Shotcrete core grades
Specify core grade of shotcrete required. Grade 1 cores are optimum, however, Grade 1 cores cannot be consistently
shot. Grade 2 cores are used for most structural members.
1.8—Evaluation of in-place shotcrete Specify acceptance/rejection criteria.
2.1—Cement
Specify if other type of cement is allowable If required, specify blended hydraulic cement in accordance with ASTM
C 595. Base selection of cement type on sulfate exposure conditions or other conditions.
2.2—Aggregate
Specify if other grading, type or tests are required. Specify criteria for acceptance. Other gradings proposed by the
contractor may be acceptable if the contractor can demonstrate satisfactory performance under similar conditions of
use.
2.3—Reinforcement
Specify type, size, configuration, minimum content, tests required, or required testing frequency and acceptance criteria.
2.5—Admixtures
A concrete mix doesn't become shotcrete until it is placed at a high velocity. Measuring air content at the 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—Fiber
ACI 506.1R—“State-of-the-Art Report on Fiber Reinforced Shotcrete” provides guidance for fiber shotcrete.
3.3.3—Surface preparation
It is recommended that steel surfaces should comply with SSPC-SP6 3.3.3.2.
3.3.5—Forms
High velocity air transporting the shotcrete mix, if not allowed to escape, may create voids at form corners.
3.4.1—Joints
Specify square joints for construction joints subject to compression loads.
3.5—Alignment control
For long spans (over 30 ft), devices that permit tightening of ground wires, such as springs or turnbuckles can be used.
3.6.1—Application
Do not place subsequent lifts until the previous lift has hardened enough to support the new shotcrete. Vertical walls
should be gunned from the bottom up unless it can be demonstrated that another method will work successfully.
3.6.2—Encasement of reinforcement Voids behind bars are not easily evident by inspection. Limiting the maximum size reinforcement bar 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—Finishing
Specify type of finish. If other than a gun finish is required, specify finish types such as rod, broom, wood float, rubber
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 compounds. 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 by or acceptable to the Architect/Engineer.
Architect/Engineer—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 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 thin coat of shotcrete preparatory to
hand finishing.
Flash coat—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 corporation, association, partnership, individual, or public body or authority with whom the contractor
enters into agreement and for whom the work is provided.
Rebound—Shotcrete material that ricochets off the receiving surface.
Sand/rock pocket—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—Submitted to the Architect/Engineer for review.
Wet-mix shotcrete—Shotcrete in which plastic concrete
with cement, aggregate, and water are first mixed together
before introduction into the delivery hose.
Work—The entire construction or separately identifiable
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
ACI
American Concrete Institute
P.O. Box 9094
Farmington Hills, Michigan 48333
ASTM
American Society for Testing and Materials
100 Bar Harbor Dr.
West Conshohocken, Pennsylvania 19428-2959
SSPC
Steel Structures Painting Council
4400 Fifth Avenue
Pittsburgh, Pennsylvania 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 Standards
ACI 301-89 Specifications for Structural Concrete for
Buildings, paragraph 5.7.1 and Chapter 9
1.4.2 ASTM Standards
A 185 Specifications for Wire Fabric, Plain, Welded
Steel for Concrete Reinforcement
A 615 Specifications for Bars, Deformed and Plain, Billet-Steel, for Concrete Reinforcement
A 820 Specifications for Steel Fibers for Fiber Reinforced Concrete
C 31
Practice for Making and Curing Concrete Test
Specimens in the Field
C 33
Specification for Concrete Aggregates
C 42
Test Methods for Obtaining and Testing Drilled
Cores and Sawed Beams of Concrete
C 94
Specification for Ready-Mixed Concrete
C 109 Test Method for Compressive Strength of Hydraulic Cement Mortars
C 150 Specification for Portland Cement
C 171 Specification for Sheet Materials for Curing Concrete
C 309 Specification for Liquid Membrane-Forming
Compounds for Curing Concrete
C 330 Specification for Lightweight Aggregates for
Structural Concrete
C 595 Specification for Blended Hydraulic Cements
C 618 Specification for Fly Ash and Raw or Calcined
Natural Pozzolan for use as a Mineral Admixture
in Portland Cement Concrete
SPECIFICATION FOR SHOTCRETE
506.2-5
C 642
Test Method for Specific Gravity, Absorption, and
Voids in Hardened Concrete
C 685
Specification for Concrete made by Volumetric
Batching and Continuous Mixing
C 989
Specification for Ground Granulated Blast-Furnace Slag for use in Concrete and Mortars
C 1116 Specification for Fiber-Reinforced Concrete and
Shotcrete
C 1140 Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels
C 1141 Standard Specification for Admixtures for Shotcrete
1.4.3 SSPC Standards
SP6
Surface Preparation Specification No. 6, Commercial Blast Cleaning
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.
1.6.2.2 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 fc′ with no individual core
less than 0.75 fc′. The mean of a set of three cubes shall equal
or exceed fc′ with no individual cube less than 0.88 fc′.
1.5—Submittals
Submit proposed mix characteristics including:
•
Proportions by weights or volumes
•
Strength
•
Water-cementitious materials ratio
•
Aggregate source and grading
•
Cement type and brand
•
Water source if other than potable
•
Proportions
•
Admixtures data sheets
•
Test results
Submit preconstruction test panel results when required.
1.7—Shotcrete core grades
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 ex-
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
Grade 1
506.2-6
Grade 2
ACI STANDARD
Grade 3
Grade 4
maximum dimension of 1 in. (25 mm) perpendicular to the
face of the core with a maximum width of 11/2 in. The end of
the core that was shot against the form may be sandy and
with voids containing overspray to a depth of 1/8 in.
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
Grade 5
ceeding 3/16 in. thick by 11/4 in. long, or one major void, sand
pocket, or lamination containing loosely bonded sand not to
exceed 5/8 in. thick and 11/4 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 flaws
such as described for Grade 3 or may have one flaw with a
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
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
SPECIFICATION FOR SHOTCRETE
to assure that remaining work complies with the requirements.
SECTION 2—MATERIALS
2.1—Cement
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:
fc′: ASTMC 42; ASTM C1140
Air content: ASTM C 173 or C 231
506.2-7
Table 2.7—Total air content for frost resistant concrete*
Nominal maximum aggregate size†
Total air content, percent‡
7
6
Less than 3/8
Greater than 3/8
* 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.
2.8—Fiber-reinforced shotcrete
ASTM C 1116
2.9—Prebagged materials
Are allowable with predampening.
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.
SECTION 3—EXECUTION
3.1—Examination
• Verify that surfaces are acceptable and are ready to receive work.
• Verify that forms are to line and grade, braced against
vibration, and constructed to permit escape of air and
rebound.
• Verify that placement and clearance around reinforcement permits complete encasement.
• Verify that surfaces to receive shotcrete have 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 thick-
506.2-8
ACI STANDARD
ness. Taper edges to eliminate square shoulders at the perimeter of a cavity.
Surface shall be saturated surface dry immediately prior to
shooting.
3.3.3 Structural/reinforcement—The surface shall be free
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.
3.3.4 Rock—Remove loose material, mud or other foreign
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 vibration. Construct forms to allow escape of placement air
and rebound.
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.
Broom or roughen the surface of freshly placed shotcrete
after shotcrete has reached initial set when subsequent layers
are to be applied.
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:
• Ponding or continuous sprinkling
• Covering with an absorptive mat or sand that is kept
continuously wet
• Covering with impervious sheet material
• Curing 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 shot-creting.
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.