An Inside Look at the Updates in ACI 301-20

A breif overview of the updates to ACI 301-20: Specifications for Concrete Construction.

American Concrete Institute ACI 301-20: “Specifications for Concrete Construction,” published by the American Concrete Institute (ACI), sets forth criteria for concrete construction that guide contractors in their daily work. The specification is commonly incorporated by reference into contract documents by the architect or engineer (A/E).

In October 2020, ACI published an expanded and revised version of the specification, including a title change. The new title, “Specifications for Concrete Construction”, recognizes that the specification covers diverse topics including industrial floor slabs and architectural concrete.

Two checklists for incorporating ACI 301 into concrete specifications are included. The first of these checklists indicates specific qualities, procedures, and performance criteria that the specifier must include in a project specification that are not defined in ACI 301-20, while the second checklist identifies choices and alternatives that the specifier can include as requirements in a specification.

WHAT’S NEW Section 1—General Requirements:

• New definitions were added for clarity. Definitions of specialty concrete applications covered in separate sections were removed. • Optional requirements include a preconstruction conference to review project requirements, acceptance criteria, and responsibilities. • Shotcrete is now included in the scope.

Section 3—Reinforcement and Reinforcement Support:

• Zinc-coated (galvanized) reinforcing bars for structures designed in accordance with ACI 318-19 must still conform to ASTM A767/A767M. However, zinc-coated reinforcement conforming to ASTM A1094/A1094M may now 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 C 1621 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. • Mineral fillers, conforming to ASTM C1797, are now permitted provided they are 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. • If Modulus of Elasticity is specified, test data for proposed 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. • Lightweight aggregate for internal curing is limited to prewetted fine aggregate conforming to ASTM C1761. • Aggregates determined to be susceptible to alkali-carbonate reactions per ASTM C1778 testing are not allowed. • Limitations imposed on concrete mixtures to be qualified to reduce the potential of alkali-silica reactivity were revised; adding a requirement for submitting supporting data for each aggregate showing expansion in excess of 0.10% at 16 days when tested in accordance with ASTM C1260, and defining limits for expansion and alkali content based on level of aggregate reactivity.

Section 5—Handling, Placing, and Constructing:

• For cold weather placements, unless otherwise specified, metallic items in concrete formwork must be above 10˚ F, and contact surface temperature of ground, subbase, or mud mats has to be above 32˚ F. • 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.

Addtional updates include sections 6, 8, 9, 11, 12, 13 and 14. The new ACI 301 provides the latest construction practices and concrete-related material information necessary for today’s contract documents. If contractors and other industry personnel are not well-versed in the changes incorporated in ACI 301-20 it can have a negative impact on a project’s budget and schedule. ACI Specifications for Concrete Construction and the ACI Field Reference Manual are both available in printed and digital formats.

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.

Find an expanded look at the updates at ForConstructionPros.com/21319401.