ACI 301-20: Concrete construction specifications

Michelle L. Wilson, FACI

Photos courtesy American Concrete Institute

The American Concrete Institute (ACI) published ACI 301-20, Specifications for Concrete Construction, in October 2020. This standard specification establishes criteria for concrete construction that can be incorporated by reference into contract documents. ACI 301 is written to the contractor.

When an architect or engineer (A/E) cites ACI 301, the document is intended to be adopted in its entirety into the contract documents. Requirements set forth in ACI 301-20 meet the minimum requirements in ACI 318-19, Building Code Requirements for Structural Concrete. Approximately every five years, ACI 301 is updated to complement the ACI 318 code cycle.

A/E can apply the reference specifications of ACI 301 to many forms of concrete construction. A notable change was made in ACI 301-20 to the specification’s title (previously the document was titled ACI 301-16, Specifications for Structural Concrete). The new specification title recognizes the breadth of the document. For example, ACI 301 covers industrial floor slabs and architectural concrete.

ACI 301-20 is organized into two parts, distinguishing basic items that are always required for concrete construction from those that may be needed on a particular project. The first five sections of the standard cover core requirements for most cast-in-place concrete. Sections 6 to 14 cover specialty applications that may be designated on a project.

ACI 301-20 contains the following sections:

  • Section 1—General Requirements;
  • Section 2—Formwork and Formwork Accessories;
  • Section 3—Reinforcement and Reinforcement Supports;
  • Section 4—Concrete Mixtures;
  • Section 5—Handling, Placing, and Constructing;
  • Section 6—Architectural Concrete;
  • Section 7—Lightweight Concrete;
  • Section 8—Mass Concrete;
  • Section 9—Post-tensioned Concrete;
  • Section 10—Shrinkage-compensating Concrete for Interior Slabs;
  • Section 11—Industrial Floor Slabs;
  • Section 12—Tilt-up Construction;
  • Section 13—Precast Structural Concrete; and
  • Section 14—Precast Architectural Concrete.

ACI 301-20 is not a complete specification until the specifier reviews and completes the instructions to the A/E, listed at the end of the document titled “Notes to Specifier.” It includes two checklists for the A/E to use in incorporating ACI 301 into the concrete specification. The “Mandatory Requirements Checklist,” indicates specific qualities, procedures, and performance criteria the specifier must include in a project specification that are not defined in ACI 301-20. The “Optional Requirements Checklist,” identifies choices and alternatives the specifier can include as requirements in a specification. These checklists provide information allowing specifiers and owners to have options to change or customize their specifications where appropriate. The specifier should review each of the items in the checklists and make adjustments to the needs of a particular project by including those selected alternatives or additions as mandatory requirements in the project specification.

What is new in 2020?

This revision expanded the scope of ACI 301 and revised many of the requirements that have been in previous versions. The scope of the document was expanded to include shotcrete, internal curing, mineral fillers, and recycled concrete aggregates. Evaluation requirements for concrete made with self-consolidating concrete and structures designed for modulus of elasticity were also included in the update.

Compliance details throughout ACI 301-20 have been updated to align with ACI 318-19. For example, ACI 318-19 saw a major reorganization of Chapter 26, “Construction Documents and Inspection.” Inspection requirements were unified in the chapter. It was also recognized many projects have roles for multiple design engineers; the updated Chapter 26 provided a framework for their coordination of work. Many of the changes in 301-20 were included to reflect the requirements in Chapter 26 on information the engineer must provide in the construction documents to achieve compliance with ACI 318-19.

An overview and notable changes to ACI 301-20 are provided in the following sections.

Section 1—General Requirements

The new American Concrete Institute (ACI) 301-20, Specifications for Concrete Construction, has been expanded to include shotcrete, internal curing, mineral fillers, and recycled concrete aggregates.

Section 1 covers general requirements pertaining to the specification; outlines work not specified; defines terms unique to the specification; and references four additional ACI standards, 138 ASTM standards, and 24 other industry documents. The referenced standards provide requirements for the tolerances, materials, and test methods cited in ACI 301-20. As part of the optional requirements in Section 1, specifiers must indicate any additional testing and inspection services, or if the sampling is desired at locations other than point of delivery, if applicable.

Notable changes to Section 1 include new definitions 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 in Section 1 now include a preconstruction conference to review project requirements, acceptance criteria, and responsibilities of each party, when specified.

Shotcrete is now included in the scope of 301-20. 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 2—Formwork and Formwork Accessories

Section 2 covers requirements for design and construction of formwork. Specifiers must indicate locations of required movement joints and water stops, along with areas where walls require form ties with a positive water barrier, and where coated or corrosion-resistant ties are required.

ACI 301-20 provides an optional requirement that the contractor must use a licensed design engineer (LDE) for formwork design if specified in contract documents or mandated by jurisdiction where work will be performed. Tolerances for formwork are provided in ACI 117, Specification for Tolerances for Concrete Construction and Materials and Commentary.

No major changes were made to Section 2 in 301-20.

Section 3—Reinforcement and Reinforcement Supports

Section 3 covers materials, fabrication, placement, and tolerances for steel reinforcement and reinforcement supports. Specifiers must indicate locations where field bending or straightening of reinforcing bars is permitted.

Tolerances for reinforcement are provided in ACI 117-10. Specifiers must include the location and tolerance for placement of welded wire reinforcement. Some projects have experienced problems during placement of the reinforcing bars because of congestion associated with embedments, openings, and other items. ACI 301-20 requires that if reinforcement must be located outside of placing tolerances, the A/E must be contacted for approval.

Notable changes to Section 3 include zinc-coated (galvanized) reinforcing bars for structures designed in accordance with ACI 318-19 must conform to ASTM A767/A767M, Standard Specification for Zinc-coated (Galvanized) Steel Bars for Concrete Reinforcement. However, zinc-coated (galvanized) reinforcement conforming to ASTM A1094/A1094M, Standard Specification for Continuous Hot-dip Galvanized Steel Bars for Concrete Reinforcement, may now be specified for applications where a lesser zinc coating thickness is permitted.

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