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Code Update: Updates to ACI 301-20: Specifications for Concrete Construction

Michelle Wilson on May 12, 2021 - in Articles, Column

In October 2020, the American Concrete Institute (ACI) published ACI 301-20: “Specifications for Concrete Construction,” which expanded and revised many of the requirements in previous versions of the standard. A notable change was the specification’s title (previously ACI 301-16: “Specifications for Structural Concrete”). The new title recognizes that the specification covers diverse topics, including industrial floor slabs and architectural concrete as well as the minimum requirements of ACI 318-19 “Building Code Requirements for Structural Concrete.”

ACI 301-20 establishes criteria for concrete construction written to the contractor and can be incorporated by reference into contract documents by the architect or engineer (A/E), and it’s intended to be adopted in its entirety. Many of the changes reflect information the A/E must provide in construction documents to achieve compliance with 318-19.

The specification is organized into two parts, distinguishing basic items that always are required for concrete construction from those that may be required on a particular project. The first five sections cover core requirements for most cast-in-place concrete. Sections 6 through 14 cover construction requirements for specialty applications. Specialty applications are designated by the A/E in the contract documents. Specifiers also must review and complete two checklists at the end of ACI 301-20: one on mandatory requirements and the other listing optional requirements. These checklists provide information allowing specifiers and owners to have options to customize their specifications where appropriate.

What’s New in 2020

Section 1—General Requirements

• New definitions were added for clarity. Definitions of specialty concrete applications covered in separate sections were removed. Specifiers need to refer to specialty sections and designate portions of the work meeting specific types of specialty concrete.

• Optional requirements include a preconstruction conference to review project requirements, acceptance criteria and responsibilities.

• Shotcrete now is included in the scope. Specifiers must designate the portion of work to be constructed with shotcrete and specify the requirements based on ACI 506.2, “Specification for Shotcrete,” and ACI 318-19.

 

Section 3—Reinforcement and Reinforcement Support

• Zinc-coated (galvanized) reinforcing bars for structures designed in accordance with ACI 318-19 still must conform to ASTM A767/A767M. However, zinc-coated reinforcement conforming to ASTM A1094/A1094M now may be specified for applications where a lesser zinc-coating thickness is permitted.

Section 4—Concrete Mixtures

• Requirements for slump flow of self-consolidating concrete (SCC) were separated from slump requirements for other concrete mixtures. Also, if specified, passing ability and static segregation should be evaluated in accordance with ASTM C1621 and ASTM C1610, respectively.

• Minimum cementitious materials requirements for floors were removed, providing more flexibility in designing concrete mixtures.

• Timelines for the prequalification of aggregates were extended. Data on types, sizes, pit or quarry locations, producers’ names, aggregate supplier statement of compliance with ASTM C33, and ASTM C1293 expansion data must be no more than 24 months old.

• Crushed hydraulic-cement concrete or recycled aggregate may be permitted if documentation is provided as required by the A/E, and its use is determined suitable for a particular project.

• Mineral fillers, conforming to ASTM C1797, now are permitted provided they’re obtained from the same sources and consist of the same types as those used in concrete represented by submitted field-test records or used in trial mixtures.

• Lightweight aggregate for internal curing is limited to prewetted fine aggregate conforming to ASTM C1761.

• If specifying modulus of elasticity, test data for proposed concrete mixtures must be submitted. The average of at least three cylinders from the same concrete sample, tested at 28 days, must meet or exceed the specified value.

• Aggregates determined to be susceptible to alkali-carbonate reactions per ASTM C1778 testing are not allowed.

• Different limitations are imposed on concrete mixtures to be qualified to reduce the potential of alkali-silica reactivity.

• Requirements for sulfate exposure categories were updated to match requirements of ACI 318-19.

• For stay-in-place galvanized steel forms, the maximum chloride content must comply with Exposure Class C1 limits. Compliance with specified chloride ion limits can be verified using the water-soluble chloride ion content or the total chloride content.

Section 5—Handling, Placing and Constructing

• For placement in cold weather, unless otherwise specified, massive metallic embedded items and bundled metallic embedded items in concrete formwork must be above 10 degrees Fahrenheit. Contact surface temperature of ground, subbase or mud mats has to be above 32 degrees Fahrenheit.

• For integrating high-strength concrete with floor systems, high-strength concrete should extend through the full floor-system depth at least 2 feet past each face of columns and walls to achieve a monolithic mass.

• Surface finish SF-2 now is established as the default formed finish. Language defining concrete exposed to view has been revised. Color, texture and bughole requirements have been clarified, and rubbed and other finish requirements have been updated.

• When curing by ponding, the temperature of ponding water must be at least 50 degrees Fahrenheit and not more than 35 degrees Fahrenheit cooler than the surface temperature of the concrete at the time the water and concrete come in contact.

• Adhesive anchor holes that are horizontally or upwardly inclined, and are designated in the contract documents to support sustained tension, must be installed by manufacturer’s instructions in at least 21-day-old concrete; and installed by personnel certified by ACI’s Adhesive Anchor Installer Certification Program or other accepted equivalent programs.

Section 6—Architectural Concrete

• Formwork must be a structurally rated plywood with a nonporous finished surface, bonded to a sanded hardwood veneer substrate, unless otherwise specified.

Section 8—Mass Concrete

• Material restrictions for specific types of cementitious materials were removed, and allowance was made for permissible changes to materials that do not require updates to the thermal control plan. Materials now are to be specified by the designer or default to cementitious materials specified in Section 4.

Section 9—Post-Tensioned Concrete

• The term “bonded post-tensioning” has been revised to “grouted post-tensioning.” The change in terminology aligns with PTI Multistrand and Grouted Post-Tensioning certification programs.

• Non-encapsulated tendons are prohibited in slabs-on-ground exposed to external sources of chlorides from deicing chemicals, salt, brackish water, seawater or spray from these sources. They also are prohibited where stressing pockets are subject to wetting or direct contact with soil during service.

• Excess lengths of tendons beyond encapsulated anchorages must be removed to ensure proper fit of encapsulation cap. Cutting of tendons should not damage wedges or compromise encapsulation systems.

Section 11—Industrial Floor Slabs

• Joint fillers must have 100-percent solids content and Shore A hardness requirements of at least 85 when measured in accordance with ASTM D2240 and an elongation below 90 percent when measured in accordance with ASTM D638.

Section 12—Tilt-Up Concrete

• The A/E may specify an alternative type of smooth panel finish other than the typical SPF-2 based on normal intended service. Wording has been revised to clarify each recommended classification based on visibility of panels.

• A smooth panel finish of SPF-3 requires preparation of mockup panels.

Section 13—Precast Structural Concrete; Section 14—Precast Architectural Concrete

• Fabricator qualifications include optional requirements for an alternative certification program from the National Precast Concrete Association (NPCA) applicable to some structural precast concrete products, except those that are prestressed.

Along with the release of ACI 301-20, ACI is releasing MNL-15(20): “Field Reference Manual,” which is recommended for any project where ACI 301 is specified. In addition to containing ACI 301-20, the new Field Reference Manual includes more than 20 selected reference documents needed to complete specifications, including references on formwork; measuring, mixing, transporting and placing concrete; concrete pumping methods; consolidation; and hot- and cold-weather concreting.

The new ACI 301 provides the latest construction practices and material information necessary for concrete construction. Producing a concise specification that takes full advantage of the content within ACI 301-20 will help avoid conflicting
or confusing requirements. 

 

About Michelle Wilson

Michelle L. Wilson is senior director, Cement and Concrete Technology, Portland Cement Association, and chair of ACI Committee 301, during the 2016-2020 document cycle; email: mwilson@cement.org.

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