Restructuring Specifications: Improving stability and durability of structural concrete with ACI 301-16

All images courtesy ACI

by Shelby O. Mitchell
What can be done to help specifiers and contractors create the most stable, durable, and resilient concrete structures possible? This challenge inspired the industry professionals responsible for updating an American Concrete Institute (ACI) standard over the summer. (ACI 301-16 is available in print and digital formats at

Every five years, ACI 301, Specifications for Structural Concrete, is updated to complement the newest version of ACI 318, Building Code Requirements for Structural Concrete. (ACI 318-14, Building Code Requirements for Structural Concrete, has been completely reorganized to reflect the designer’s perspective. More details are available at During the most recent review cycle, ACI 301 Committee on Specifications for Structural Concrete not only updated technical requirements, but also created a more user-friendly reference specification for nearly all forms of structural concrete.

The committee’s approach was twofold. Specific wording was one area of focus: removing redundancies, making language more self-explanatory, and improving definitions of terms. The specification also had to maintain a broad scope, since ACI 301-16 is used across a wide range of climates, geographic areas, and social conditions around the world.

Providing clarity
One way of encouraging specifiers and contractors to adopt a specification is to make it easier to understand.

“We spent a lot of time cleaning up the language to make it more clear for the user,” says Michelle Wilson, the committee’s chair (and director of concrete technology for the Portland Cement Association [PCA]). “This is a contract document written in mandatory language, so it’s very important to remove wording that is confusing or subject to interpretation.”

The committee clarified many commonly used terms. ‘Architectural concrete,’ for example, is defined in the specification as:

concrete that is typically exposed to view, is designated as architectural concrete in contract documents, and therefore requires care in selection of the concrete materials, forming, placing, and finishing to obtain the desired architectural appearance.

Many provisions have been spelled out to clearly indicate their intent. For example, the requirement for water used for curing concrete previously stated:

Unless otherwise specified, water complying with the requirements for ASTM C1602/C1602M [Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete] is acceptable as curing water.

ACI 301-16 now reads:

Unless otherwise specified, do not use seawater or water containing substances that will discolor or impair the durability of a concrete member.

Throughout the specification, consistent language differentiates between required and optional provisions. The phrase “as specified in the contract documents” indicates a mandatory checklist item and tells specifiers they must take action. “Unless specified otherwise” means something is optional. This flags items specifiers may want to review, and tells contractors alternatives may be available. This ‘trigger language’ has been reduced from around 30 different words and phrases to just five or six in the new specification.

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