Addressing Embodied Carbon as a Sustainability Issue

The use of concrete in the construction of new infrastructure is a significant contributor to the widespread challenge of reducing embodied carbon. Embodied carbon are the carbon dioxide emissions that result from manufacturing, transportation and installation of building materials. This differs from operational carbon, which are the emissions that are produced from a facility’s fuel combustion or other industrial processes. Together, embodied and operational carbon form the overall carbon footprint of a building or other infrastructure component.

In 2021, roughly 6% of the world’s carbon emissions were a result of 2.9 billion tons of concrete placed. The prevalence of this human-made material means the use of concrete poses a significant sustainability issue.

Some solutions that companies can implement to combat embodied carbon and provide a lower carbon footprint include:

• Portland limestone cements (PLC, Type 1L). PLCs increase the percentage of ground, unprocessed limestone in Portland cement from 5% to 15%. By replacing the carbon intensive clinker with a minimally processed mineral, the resulting concrete has an immediate near-10% reduction in its embodied carbon.
• Traditional supplementary cementitious materials (SCMs). Cement manufacturers are standardizing their blends of traditional cement with traditional SCMs (such as blast furnace slag, coal ash, natural pozzolan, etc.), making the final product much more consistent and predictable. These cements utilize industrial byproducts to replace the carbon-intensive ingredient in concrete, but some have a limited long-term future due to industrial decarbonation that will bring an end to coal-burning power plants and steel blast furnaces.
• Second generation SCMs. A collection of newcomers will help offset the loss of traditional SCMs. Some of them are already in use and ramping up manufacturing, such as limestone calcined clays and pozzolans made from recycled glass. Others, such as bio-mimicking and electrolyzed cements are still in the experimental phase.
• Carbon dioxide utilization. These solutions introduce captured carbon dioxide (CO₂) into fresh concrete. The ensuing early age carbonation makes the concrete stronger, allowing for a reduced cement content, while permanently sequestering captured CO₂.
• Optimizing aggregate grading. The selection and addition of an intermediately graded aggregate (between the sizes of the traditional gravels and sands) can reduce the volume of paste that is required in a concrete mix. The resulting cement reduction may offset the cost of the additional aggregate.
• Strength-enhancing admixtures. A new generation of strength-enhancing admixtures seed the cement paste with nano-particles that lead to early and late-age strength gains. The added strength allows for the specification of a lower cement content, and an ensuing reduction in embodied carbon.
• Recycled content. Recycled (crushed) concrete can be utilized as aggregate in most concrete mixes up to 25%. This would reduce manufactured concrete (and aggregate use), ultimately reducing the carbon footprint of the concrete’s life cycle.

For every cubic yard of normal-strength concrete without any of these carbon mitigation additives, around 500 kg of CO₂ are are emitted. In addition to the previously mentioned solutions, companies have other ways to implement sustainability measures. Companies can form a sustainability program, where key people can focus on working toward more sustainable products and improve overall company processes from a corporate level. This sustainability program should also examine raw materials and identify ways to minimize waste materials and recycle products.

In addition to using sustainable concrete production practices, using a green construction process also minimizes carbon emissions. This can be done by maximizing structural efficiency during the design phase and using salvaged materials to minimize waste produced. Overall company energy consumption processes should also be examined to determine if any other sustainability measures can be implemented.

The General Services Administration (GSA) announced on May 16 a test program that draws from the Inflation Reduction Act, enacted Aug. 16, also known as the Climate Act. The statute provides $2.15 billion for GSA to use low-embodied carbon materials for its federal buildings projects. The pilot program is a signal to manufacturers that it requires Environmental Product Declarations (EPDs) for materials procured with Climate Act funding. Some types of products do not yet have published EPDs with embodied carbon included.

Widespread implementation of sustainable solutions requires companies to conquer the challenges that prevent impactful change. To successfully implement sustainable concrete alternatives, companies must invest in trainings and knowledge-sharing opportunities involving challenges and solutions for embodied carbon. Additionally, continued research and development into concrete alternatives should be pursued to minimize embodied carbon and provide for a more sustainable future.

Construction sustainability is crucial for resilient infrastructure and a green tomorrow. Learn how we are working to minimize carbon emissions with strategic design and construction practices.