Sustainable Building Solutions with UHPC – Case Studies (ACI Spring 2024, New Orleans, LA) The Delaware River and Bay Authority (DRBA) now has an ultra-high performance concrete (UHPC) overlay on the entire deck of one of its twin two-mile-long bridges known collectively as the Delaware Memorial Bridge. This is the first long-span bridge and the first suspension bridge with a complete UHPC overlay in the United States. Construction began in September 2022 and was carried out in three phases and completed in November 2023. The UHPC overlay was placed on over 51,000 square meters (550,000 square feet) of deck while keeping traffic flowing in both directions across the twin bridges. This project was preceded by a detailed lifecycle cost analysis followed by a small pilot project which helped guide project decision-making. The lifecycle cost analysis, which was focused on construction time and cost, showed a clear economic advantage to performing a UHPC overlay versus deck replacement or placing other overlay products. However, revisiting the comparative analysis from a sustainability perspective shows that the UHPC overlay is also the most sustainable solution. UHPC contains approximately twice as much cement as conventional concrete contains, and cement is known as a significant source of carbon dioxide emissions. However, deck replacement would require approximately three times as much concrete and a construction duration that is three times longer, which more than offset the higher carbon footprint of the UHPC material. Similarly, while other overlay materials may also have a lower carbon footprint, they would have to be replaced at least once, if not more, during the anticipated life span of the UHPC overlay. The presentation will provide a more detailed analysis of the sustainability of the UHPC overlay on the Delaware Memorial Bridge, while also briefly presenting how the full overlay project transpired and how the completed project is performing.

123 Forum - Should 3D Printing be Codified? (ACI Spring 2024, New Orleans, LA) Additive Manufacturing (AM) with concrete, also known as 3-D Concrete Printing (3DCP) and more recently Additive Construction (AC) with concrete, is an emerging and rapidly evolving technology in the construction industry. This approach to concrete construction has the potential to change the way cementitious materials are used to create infrastructure components. Automating the placement of concrete materials may improve construction efficiency by eliminating the need to erect formwork, improve infrastructure durability by providing precise control of concrete formulations, and improve construction safety by removing humans from hazardous working environments. Rapid construction enabled by 3DCP techniques can provide shelter to communities affected by natural disasters, build with local materials in hostile environments (e.g., military and mining applications), build taller wind turbine towers to access higher energy winds, and repair concrete in areas which are hard to access with conventional construction equipment. The concrete design and engineering community lacks sufficient knowledge about the performance of 3DCP structures subjected to designed loading scenarios to properly design 3DCP structures for a given application. The role of the printing process in determining the failure mode and a detailed understanding of the relationship between the 3DCP structure’s constituent material properties and structural response are critical to developing performance-based standards and guidelines for 3-D printing construction techniques. Developing this knowledge base and coupling it to measurements of concrete materials in the 3DCP process would mark a significant step toward revolutionizing concrete construction.