August 31, 2023

Concrete can be part of your sustainability equation

Sempel

Lindeman

Concrete is a major source of carbon pollution. With increasing focus on sustainability and environmentally-sensitive choices, clients and firms alike in AEC are naturally exploring more sustainable materials like mass timber. However, not every project can afford or structurally use the sustainable benefits of wood. At the end of the day, we will all continue living and building in a world that depends heavily on concrete.

Once we accept this, the industry’s mandate is clear. We must vastly improve our use of this material and affect large-scale change through systematic choices made on projects being built today. Both will be a direct result of daily work and design choices, working through the practical constraints of each new project.

High schools still need to be built

While sustainable choices are important, creating safe and well-performing buildings always takes precedence. The new Rainier Beach High School, designed by Bassetti Architects, is targeting LEED Platinum and employs green building strategies. However, the site has poor soils and groundwater issues, requiring atypical structural foundation construction.

After thorough design, study, and meticulous review, Coughlin Porter Lundeen’s structural team chose an aggregate pier foundation system with a thick mat slab to provide settlement and liquefaction mitigation for the structure. As part of internal review, the structural team used the Tally analysis tool to perform a Life Cycle Assessment (LCA) to quantify the initial embodied carbon in the structure, and create targets for embodied carbon reductions. The EC3 tool was then used to further refine the LCA and embodied carbon studies. The latter revealed changes that could be made to concrete strength and cure times to lower the carbon cost without impacting building safety. Working with Bassetti Architects, we set performance targets for Global Warming Potential in the specification and asked the subcontractor to propose mix designs that would meet the targets without impacting project cost.

Photo courtesy of Bassetti Architects [enlarge]

Despite adverse soil conditions that required a thick concrete mat slab, the design team succeeded in reducing the new Rainier Beach High School’s carbon footprint.

The resulting design required more concrete than original estimates, but will result in a far safer structure for the Rainier Beach community. Despite the inherent site challenges, we were able to lower the embodied carbon through our design and review process, so this was a win-win.

A typical high school requires approximately 69,500 cubic feet (2,575 CY) of concrete for sidewalks, physical education, and outside activities in site flatwork alone. One cubic yard is equivalent to approximately 533 pounds of CO2 for the acquisition of raw materials, manufacturing, and transportation to the site. This means that a high school in the Pacific Northwest could produce 1,369,810 pounds (685 tons) of CO2 — and that is before anyone even puts a building on the site.

Knowing this, our civil team regularly uses Type 1L cement (in place of standard Portland cement) to provide a 10% reduction in embodied carbon of a concrete mix without increasing cost on Seattle-area projects. A high school site like this example could use Type 1L and realize a carbon savings equal to 74 acres of U.S. forest a year.

While we all use civil engineering-designed spaces on a regular basis, even the best designs go unnoticed, which is typically their purpose. But that doesn’t mean that their hidden potential should also be ignored.

Engineers with the right approach can vastly improve a project in ways that others won’t ever see, like when measuring and tracking embodied carbon. Our firm has spent years studying these problems with our Sustainability Task Group, talking to clients and vendors in the Pacific Northwest, and putting in the daily work to reach sustainability goals as early in the design process as possible.

Sustainable choices don’t always cost more

It is common for clients to think that sustainability considerations automatically increase costs. For example, Jefferson Hospital was pleasantly surprised when told they could reduce their embodied (and operational) carbon on their South Campus replacement and addition with no cost increases. Their original goals were highly focused on providing the best healthcare they could; they valued sustainability and equity too, but leaned into the design-build team to develop more specific goals with a focus on cost-neutral strategies. We worked closely with ZGF Architects and Abbott Construction to understand how easy adjustments could be made to realize large carbon reductions for this project.

Jefferson Healthcare is located in Port Townsend. This means that large Seattle concrete mix producers can’t be used on this job because the travel time would be too long for the material to be usable per ASTM code. In addition, while most of the major concrete providers in Seattle have numerous concrete mixes with Environmental Product Declarations (EPDs), many smaller concrete providers do not yet. EPDs are an important first step toward transparency in our building materials. Without EPDs, it is harder for smaller providers to show how sustainable their different mixes are, and for us to calculate the total embodied carbon of a building or site they are working on.

For the Jefferson Healthcare project, our team used the EC3 tool to produce a total estimate of the embodied carbon and ZGF’s Concrete LCA Tool to estimate savings from the proposed concrete mix designs. This showed where to focus efforts and achieve realistic reduction goals. The team then contacted the local concrete provider chosen for the job, Cotton Shold, and made the case for investing in EPDs—which they did for the first time, specifically for this project, at a relatively low cost—to capture the specific savings in the local supply chain.

This is an important step to track the embodied carbon produced by using their products, and Cotton Shold appreciated the opportunity to provide a more sustainable option to their clients on the Olympic Peninsula.

Using the anticipated concrete mix EPDs from Cotton Shold, the final design is estimated to realize a Global Warming Potential impact reduction of 25,000 kgCO2e, equivalent to the carbon sequestration of 300 acres of U.S. forest for one year. All without increasing the project’s budget and staying firmly aligned with the client’s goal of providing the best healthcare possible for the Port Townsend community.

The best teams translate sustainable goals into practical, achievable design choices. To do this, they create multiple iterations to fully explore the expected outcomes from key points of consideration, all while respecting and working within budget, performance, and code constraints.

There are many sustainable concrete options being researched and some are even being tested on site, but few are at a scale large enough to implement effectively in the Pacific Northwest. We can’t sit back and wait for material advances to catch up with our community and regional needs. Instead, engineers and other AEC insiders must push the industry forward, using existing tools and materials, to make the carbon reduction advances the Pacific Northwest needs now.

Jackie Sempel is a leader in Coughlin Porter Lundeen's civil practice and co-chairs the firm's sustainability task group. Laura Lindeman is a structural project manager for Coughlin Porter Lundeen, leads integration of the Embodied Carbon in Construction Calculator (EC3) tool as a firm-wide standard for carbon tracking, and co-chairs the firm's sustainability task group.

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