Using Green Concrete to Build The Reed, Chicago
Session: Track E: Structural Challenges: Designing for Endurance
Director of Engineering, McHugh Construction
Traditional concrete is economical and reliable, but also carbon-intensive, primarily due to the energy demands of Portland cement production. As a result, many recent proposals in sustainable construction have replaced concrete with low-carbon materials such as mass timber. However, new low-carbon concrete mix designs have total embodied carbon levels competitive to other low-carbon systems for tall building construction. The Reed, a residential high-rise under construction in Chicago using a new green concrete mix, exceeded Lendlease’s specifications for reduced global warming potential (GWP) per cubic yard of concrete.
A life cycle analysis (LCA) performed in the design phase considers how multiple structural systems and material choices impact the building’s embodied carbon and operational carbon; meet challenges related to architecture, sustainability, constructability and economics; and lower GWP while also meeting the project’s budget and schedule. By replacing up to 75 percent of the mix’s Portland cement with supplementary cementitious materials and/or inert “fines” (byproducts of industrial processes whose use in concrete diverts them from the waste stream), the concrete’s embodied carbon is reduced by up to 40 percent relative to baseline mixes. Using low-carbon concrete also leverages the expertise and efficiencies of the mature concrete construction market, resulting in significant material and schedule savings.
The Reed is establishing a new benchmark for sustainable concrete high-rise construction in Chicago. By expanding architects’ and engineers’ palette of sustainable materials, the design and construction of low-carbon buildings can be enabled by eliminating hurdles related to budget restrictions, limited manufacturing and construction capabilities, or raw material supply shortages.