Nominee
Martin Marietta AZ - ASU Interdisciplinary Science & Technology building 7 (ISTB-7)
Category
Innovative Project
Description
As the concrete producer for Arizona State University’s Interdisciplinary Science and Technology 7 (ISTB-7) building Martin Marietta AZ was challenged to develop a mix design to help lower the project’s embodied carbon footprint. Given the carbon intensive nature of cement, the team set out to utilize a post-consumer by-product (fly ash) to reduce the total amount of Portland cement in the building structure by at least 40%. In addition to the high criteria sustainability requirements, including pursuit of LEED Platinum Certification, the concrete needed to be aesthetically pleasing, since it would be used in Class A architecturally exposed columns, walls, stairs, deck soffits and polished concrete floors. Although 40% cement-replacement mixes are not uncommon, they are usually used in a targeted approach to control the heat of hydration. With this project, the mix was applied whole scale through the entire building. For Martin Marietta delivering concrete with widescale application – especially one with architectural aspects required ensuring the entire team -- design, construction, materials suppliers including the admixture partners worked together to find the best solutions for the application.
Concrete mix and specifications
• 4,000 PSI for slab on grade, grade beams, caissons, caisson caps and foundation walls; 5,000 PSI for shear walls and stairs; 6,000 PSI for elevated slabs; and 8,000 PSI for columns
• SCM: Class F fly ash
• Aggregate: One-inch rock
• GCP admixtures WRDA 64 and Adva 195
Evidence
Early on Martin Marietta utilized an NRMCA industry wide EPD to establish a baseline against their typical approach to the mixes needed for the project. This helped the team discuss different mix design scenarios and how to optimize the use of locally available resources. Using a high fly ash mix design for the 6,000 PSI mix was not only beneficial as a low-carbon approach but as for its ability to reduce permeability to water and produces a densified product. With the architectural needs in mind as well the admixture package this gave Martin Marietta the opportunity to keep the water/cement ratio low while achieving high strength as well as the workability to place the concrete very easily. The use of high range water reducer (Adva) and the mix design resulted in fewer bubbles against the surface than midrange water reducers. This created a smoother finish on the forms. Martin Marietta's mix designs helped allow the use of a 40% fly ash replacement of the Portland Cement which in turn reduced cement content directly impacting CO2. As a final step Martin Marietta in partnership with their admixture supplier's EPD tool compared the original baseline mix against the final optimized design. Through this comparison Martin Marietta was able to estimate the CO2 reduction of one mix design by 59kg CO2e per cubic yard which equated to approx. 624,000 kg CO2e savings on the decks alone.
The project was completed in late 2022 and reached its LEED Platinum Certification. It was also awarded the ENR Southwest project of the year for 2022.
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