THE ROLE OF ACI 301, “SPECIFICATIONS FOR STRUCTURAL CONCRETE”
With the plethora of concrete standards and codes that apply to concrete construction, the role and purpose of ACI 301 can become a little obscure. The questions are almost as plentiful as the applicable standards and codes; there are dozens of them, if not hundreds. What is ACI 301 anyway? What is the difference between ACI 301 and ACI 318 (the concrete code)? This edition of Speaking in Code will discuss in some depth the role and purpose of the most functional, practical, and fun concrete standard of them all – ACI 301.
ACI 301 describes itself as a reference standard that the architect/engineer can apply to any construction project involving structural concrete by citing it in the project specifications. The ACI 301 standard is certainly that and more – much, much more. As to the differences between ACI 301 and ACI 318, there are many. While ACI 318 (the code) presents minimum requirements related to construction methods and materials relative to public safety, ACI 301 presents more than the minimum requirements on construction methods and materials relative to the actual concrete construction. ACI 318 strives to guarantee a safe design with an emphasis on public safety but not necessarily good construction. ACI 301 is all about good concrete construction practices.
Let’s talk history before we plunge deeper into the technical stuff. ACI 301 is relatively young and was actually adopted by the American Concrete Institute (ACI) in 1972. ACI 318 was created much earlier (1941) when it replaced an earlier concrete standard known as the “Standard Building Regulations for the use of Reinforced Concrete,” which was created in 1910. This first concrete construction standard created in 1910, by the predecessor of ACI, consisted of only 14 pages. Think of it — a standard that was only 14 pages long to tell you all you needed to know about the finer points of concrete construction!
ACI 301, “Specifications for Structural Concrete,” is updated about every five years in order to complement the ACI 318 code cycle. It should be noted here that ACI 301 received a title change in the October 2020 edition; it is now “Specifications for Concrete Construction.” This is an appropriate change for the ACI 301 standard that (among other things) really deals with concrete construction. It addresses: 1) building the concrete forms; 2) placing concrete reinforcement and supports; 3) concrete mix designs; and 4) handling, placing, and finishing the concrete according to the project concrete specifications.
If you are not impressed yet, you should realize the words in that last sentence are abridged from about five to six pages of comprehensive verbiage in ACI 301. In addition to the four areas outlined above, ACI 301 also addresses dozens of referenced standards, submittals or certificates of compliance, testing and inspection methods, concrete protection criteria, and acceptance criteria pertinent to the structure.
ACI 301 includes 14 different parts called “sections.” The first five sections are basic and deal with all concrete construction and the other nine sections are concrete specialty 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, Finishing the Concrete
- Section 6 Architectural Concrete
- Section 7 Lightweight Concrete
- Section 8 Mass Concrete
- Section 9 Post-Tensioned Concrete
- Section 10 Shrinkage-Compensating Concrete
- Section 11 Industrial Floor Slabs
- Section 12 Tilt-Up Construction
- Section 13 Precast Structural Concrete
- Section 14 Precast Architectural Concrete
Pages 51-64 Notes to Specifier and Mandatory and Optional Checklists
The first five sections of ACI 301 are about the basics of concrete construction and they apply to all aspects of concrete construction work on any type of project. The specification covers construction of cast-in-place concrete, architectural concrete, lightweight concrete, mass concrete, post-tensioned concrete, industrial floor slabs cast on ground, tilt-up construction, precast structural concrete, and precast architectural concrete. These sections cover materials and proportioning of concrete; reinforcement and prestressing steel; production, placing, finishing, and curing of concrete; formwork performance criteria and construction; treatment of concrete joints; embedded items; repair of surface defects; and finishing of formed and unformed surfaces. Provisions governing testing, evaluation, and acceptance of concrete as well as acceptance of the structures are included.
These five sections apply to ALL projects where this specification is referenced; this means practically ALL projects because ACI 301 is incorporated into project specifications by reference. Sections 6 through 14 apply ONLY if that type of work is designated in the contract documents.
ACI 301 is the default concrete specification for the industry and attempts to incorporate the requirements of the ACI 318 concrete code. ACI 301 is written by specifiers especially for contractors. It is a mandatory document written in mandatory language. The last ten pages of this specification include a “Mandatory Requirements Checklist” and an “Optional Requirements Checklist.” The specifier MUST include the mandatory requirements in the project specifications. The “Optional Requirements Checklist” offers the specifier choices and alternatives. If the specifier elects to insert some of the optional items into the project specification, then they become mandatory and enforceable.
For decades, ACI 318 (concrete code) set forth the code criteria used to establish acceptance of the proportions of concrete mixtures. The 2014 edition of ACI 318 deleted all of the previous code verbiage related to acceptance criteria for the proportioning of concrete mixtures and passed that responsibility to ACI 301. Chapter 318, Section 220.127.116.11, states that “Concrete mixture proportions shall be established in accordance with Article 4.2.3 of ACI 301.” Article 4.2.3 requires that strength test records used for establishing and documenting concrete mix proportions shall not be more than 24 months old. All concrete mixtures used on project work must comply with ACI 301, Article 4.2.3, and there are lots of rules and guidelines with which the concrete mixtures must comply.
There are basically two acceptable methods stipulated by ACI 301 with which concrete mixture proportions must comply:
1. Sample standard deviation method – Test data used to calculate standard deviation shall represent materials, mix proportions, QC procedures, and climatic conditions similar to those expected in the work. Test data must be based on test groups of from 15 to 30 consecutive compressive strength tests to determine average compressive strength.
2. Trial mixture method – Establish mix proportions based on trial mixtures to comply with the following: Make at least three trial mixtures for each concrete class with a range of proportions that will encompass the specified design compressive strength of the mix proposed for the project. There is a great deal of acceptance criteria with which the trial mixes must comply in order to comply with ACI 301, Article 4.2.3.
ACI 301, Article 4.2.3, does allow for the possibility of concrete mixes to be approved even if they fail to comply (strictly) with 4.2.3 if approved by a licensed registered design professional. All project concrete mixtures must also comply with the criteria set forth in the exposure categories in ACI 301, Section 18.104.22.168.
The order of preference can be confusing when conflicts between ACI 301, ACI 318, and the IBC code occur:
- The ACI 301 specification becomes part of the contract document and provides requirements for the contractor
- ACI 301 governs for construction within its scope except contract documents govern if there is a conflict between the two
- If ACI 301 requires less stringent acceptance criteria than ACI 318, then the ACI 318 criteria governs because all construction methods and materials must comply (at least) with ACI 318; ACI 318 code is the minimum acceptable concrete code criteria
- If there is a conflict between the statewide code and any of the other codes or standards, then the statewide code rules
- The statewide code and the IBC code (together) stipulate the minimum acceptance criteria for construction methods and construction materials
- Generally, when there is a conflict between two applicable codes, the more stringent requirement is enforced
It should be emphasized that this entire conversation has been about commercial construction, not residential construction. This distinction is important on several levels. Commercial construction is building for commercial purposes. Stores, offices, and schools are examples of commercial construction. Residential construction focuses on buildings people will live in. Homes, apartments, and housing complexes are all forms of residential construction.
Concrete construction for residential construction is covered by a different building code – ACI 332, “Residential Code Requirements for Structural Concrete.” ACI 332 does cite ACI 301 as a reference code; therefore, ACI 301 concrete acceptance criteria does come into play on residential construction when applicable. While much of the ACI 332 criteria is similar to the ACI 301 and ACI 318 criteria, there are key differences. ACI 332 criteria cites maximum slump ranges for the exposure classes of concrete – ACI 301 and ACI 318 do not. ACI 332 does invoke ACI 318 (concrete code) criteria whenever the residential structures exceed the limits of ACI 332. ACI 332 exists for residential construction and is applicable for one- and two-family dwellings and multiple single-family dwellings (townhouses).
But Wait — We Have a Lot More to Say! For a complete picture of the Code and how it relates to Special Inspections, F&R would love to provide a virtual (for the time being) AIA accredited Lunch & Learn presentation to the professionals at your firm.
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Alan S. Tuck, Director of Code Compliance & Training | T 540.344.7939 | M 540.798.4440 | email@example.com