ACI Code-323-24:
Low-Carbon Concrete
The newly published ACI Code-323-24 provides provisions for concrete where reduced global warming potential (GWP) is required. A first-of-its-kind document, this code is an important step forward in reducing the embodied carbon of concrete construction.

Why a code to reduce carbon in concrete is important.
Production and placement of concrete is responsible for an estimated 7% of total carbon emissions worldwide. Recently, significant policy and legislative efforts have been undertaken to limit the embodied carbon associated with concrete and other construction materials. This action has taken place at the municipal, state, and federal levels simultaneously, leading to varied and inconsistent approaches to limiting the embodied carbon of concrete.
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ACI Code-323-24 provides a standardized method, developed by concrete and sustainability experts, to limit carbon emissions associated with concrete production and placement.
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The first edition of the code, published on November 2, 2024, has a narrow scope focused on up-front embodied carbon emissions for cast-in-place concrete systems. It is expected that future versions of the code may expand to examine more aspects of sustainability, further life-cycle stages, and a broader range of concrete systems.
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The code is entirely material technology agnostic, meaning that it does not require or limit the types of concrete technologies that can be used in concrete mixtures. The code focuses on limiting global warming potential (GWP), and the methods for achieving that GWP are left up to the Licensed Design Professional (LDP) and their team to determine.
How ACI Code-323-24 aids in the specification of lower carbon concrete.
ACI Code-323-24 takes a modified carbon budget approach to reducing carbon emissions associated with concrete materials. The code provides provisions for LDPs to determine a weighted GWP performance requirement for the concrete used in their project. This weighted approach allows engineers the flexibility to use concrete systems that may be needed for specific applications without sacrificing performance and constructability requirements. Therefore, if an LDP needs to use a system with a relatively high GWP, they can offset this by using a low GWP system in another area of the building. This provides LDPs with better tools than what are available in the more common carbon limit per concrete class approaches.
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The code follows a three-step process. First, the project type to be completed must be determined, i.e. building, bridge, pavement or hardscape, or other structure. For Step 2, based on the type of project and the size of the project construction, LDPs will then determine the appropriate compliance path: Tier 1, Tier 2, or Tier 3. For Step 3, the engineers will need to produce the appropriate information required by either Tier 1, Tier 2, or Tier 3 compliance paths.
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The Tier 1 compliance path, currently reserved only for large construction projects, will require LDPs to define a weighted GWP limit for the cast-in-place concrete used on their project. This weighted GWP will be a reduction from the local GWP benchmark, as defined by the adopting jurisdiction. LDPs will also be required to document all concrete mixtures used on the project and the strategies that they will use to achieve lower embodied carbon in the concrete used in their projects. For Tier 2 compliance, reserved for medium sized projects, LDPs will be required to determine what the weighted GWP limit for their project would be if they were a Tier 1 project, but are not required to meet that reduction level. They will also have to document the strategies that they will use to achieve lower embodied carbon in the concrete used in their projects. Finally, for a Tier 3 project, or the smallest projects, the LDPs are required only to document the concrete mixtures used on the project and any strategies that they will use to achieve lower embodied carbon in the concrete used in their project. This current approach places the most significant burden of compliance on only the largest projects for the initial version of the code.
Learn where using a reduced-carbon concrete is a standard.
The road to ACI Code-323-24 adoption can vary depending on the state and country which may be interested in adopting it. The process of official adoption into state building codes can take several years; however, many groups have expressed an interest in the adoption of Code 323 in the near future.
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Currently, many areas have adopted buy-clean policies and requirements that could benefit from the use of ACI Code-323-24 as a tool for determining the GWP performance requirement for concrete. These include: Washington State, Oregon, California, Colorado, Minnesota, New York, New Jersey, and Maryland. Bills are under consideration in Illinois, Pennsylvania, Massachusetts, Rhode Island, Connecticut, and Virginia.
