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2025 Nominees

Project Name

One Milestone

Description

The One Milestone project specification included an initial goal of 25% embodied carbon reduction relative to the NRMCA Baseline. The final building product will be a Boston-area higher education enterprise research campus consisting of 600,000 square feet of mixed-use development including 400,000sf of Class A life science space.

This combined team of Arrowstreet, SGH, McNamara Salvia, Turner and their Self-Perform Operations (Turner SPO) and Boston Sand & Gravel (NRMCA Member) focused on the carbon calculation of the concrete mixes and challenged themselves to be tactical in reduction opportunities. Early alignment with the McNamara Salvia and their willingness to proceed with a performance based specification (vs. prescriptive) allowed for more creativity during preconstruction. In this stage of the project, multiple low-carbon concrete solutions were developed, approved, and continually checked. The concrete design and ready mix approach is complete. The final calculation was based on approved mix design and actual quantities of concrete placed.

The construction of this project is being managed by a Turner|Janey|J&J joint venture. The project has ~28,000 cubic yards of concrete, with ~18 unique mix designs. This motivated project team implemented multiple strategies and developed novel approaches. By leveraging early engagement, a 49% reduction in embodied carbon reduction was achieved, exceeding the project's initial goal of 25% relative to the NRMCA Baseline

The team is implementing this approach as a best practice on all projects and will evaluate all mix designs during preconstruction. To educate the trade market who are only becoming familiar with carbon targets, there is a now a calculator for bidders to use along with their competitive pricing so that both the economic and environmental value of mix designs can be evaluated side-by-side. We are no longer just leveling the bid pricing, but also leveling for carbon intensity.

The approach is easily replicable on other projects as neither the structural elements or concrete materials are particularly uncommon. Structural mats are standard and can easily be comprised of cement, aggregates, and binders that are already available at local batch plants.

Evidence

Step 1 - Set an Achievable Goal
Each mix design had a unique producer's identifier for a given mix at the Boston Sand & Gravel plant. The team began by evaluating the highest-volume mixes where a smaller % reduction could lead to many tons of carbon savings. Mix Design # 304164 was used for the structural slab on metal deck (SOMD) and non-structural mud mat which acts as a working surface during the project. This mix had an estimated quantity of 11,000cy so even a small reduction would lead to big results. By using readily-available slag to replace 25% of the cement, a 33% reduction in the embodied carbon was realized for this mix design.

Step 2 - Raise the Bar
The team reviewed the structural mat foundation with a 8000 psi, whose thickness varied from 3' to 11' and was comprised of Mix Design # 398176. In this case, the team developed the most innovative mix: a 60% replacement of cement with slag and fly ash, which resulted in a 66% reduction of embodied carbon from the NRMCA Baseline. Even though the mix was developed with standard Supplementary Cementitious Materials (SCMs), this particular mix was brand new so additional test data was needed to build a backlog of data and satisfy the compressive strength requirement. Mockups had to be completed for the engineer's review and approval and Boston Sand & Gravel had to develop product-specific EPDs.

Step 3 - Keep Going!
In a first-ever placement, Turner, Boston Sand & Gravel, and McNamara Salvia created an opportunity for Sublime Systems' first ever field validation pour. Sublime Systems is a pioneer in cement manufacturing and developed a means of manufacturing cement without fossil fuels. Testing confirmed that the Sublime cement performed according to ASMT C1157. Piloting this innovative product in a low-risk placement builds confidence in the market and provides opportunity for practical workforce feedback.

Added Benefit!
The mix’s lower heat signature meant that less crushed iced was required. This, combined with an SGH-engineered moisture retention method in lieu of wet-curing, meant that the project reduced the amount of required potable water. This is in perfect alignment with Turner’s commitment to decrease potable water consumption by 10% by 2030.

This effort won the BE+ Green Building Showcase Award for Construction Innovation.

Images

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