ACI Code-323 Low-Carbon Concrete

Low-Carbon Concrete and Sustainability of Wind Turbine Foundations

“ACI Code-323 Low-Carbon Concrete - Code Requirements and Commentary” is a draft ACI standard currently open for public discussion from March 31 to May 15, 2024. ACI members are invited to login to download the draft Code and its associated comments form from ACI’s website concrete.org and provide comments.

The proposed Code defines Low-Carbon Concrete (LCC) as concrete that is designed with reduced upfront embodied Global Warming Potential (GWP). GWP is an index used to determine the energy absorption caused by the emission of different gases associated with a product, normalized to an equivalent mass of carbon dioxide over a period of 100 years.

The proposed Code is in addtion to and does not subsitute governing building or structural design codes and standards. Hence, it does not address strength, stability, serviceability, durability, integrity of concrete structures, or construction means and methods. However, it kicks in where reduced GWP is required for cast-in-place concrete structures by the Authority Having Jurisdiction or the entity adopting it, such as the project owner.

It is a well established fact that the carbon footprint of reinforced concrete is attributed to two main components: concrete (primarily Portland cement production) and steel reinforcement. The proposed Code is focused on the concrete component; i.e., the concrete mix designs and their associated volumes used on a project.

From our scan of the draft document, the Code is based on the premise that the enforcer of the code (Authority Having Jurisdiction or entity adopting it) would require that the weighted average of the GWPs for the concrete mixes used on a project be equal to a benchmark weighted average where the GWPs of the different concrete mix designs are determined by the enforcer of the Code. When the enforcer of the Code does not provide benchmark GWPs, the Code lists GWP benchmarks for different regions of the country and for different concrete compressive strengths.

The Code has provisions for cast-in-place concrete used in buildings, pavements and hardscapes, bridges and other structures.

Given the huge amounts of concrete used in wind turbine (WTG) foundations, the Code has the potential of making wind energy even more sustainable. Adopting this Code would complement other efforts targeting steel reinforcement and blades. However, the big unknown at this stage is the cost impact of enforcing this Code. The cost impact will become clearer as we implement the Code on real life projects. Incentives, in various forms and using various mechanisms, could be the needed catalyst to promote its adoption.