2024 Award Winners and Nominees
Project Name
Presidio Tunnel Tops
Description
Back in 1993, work began to replace the seismically unsafe Doyle Drive, and the progressive idea to construct two tunnels with parkland on top was born. Countless hours of community input, collaboration between the Presidio Trust and the National Park Service, and fundraising (to the tune of $98 million) by the Golden Gate National Parks Conservancy have resulted in Presidio Tunnel Tops, a park that will change the face of San Francisco.
In 2014, the “Partnership for the Presidio” launched an international design competition to find a team to work with the community to design Presidio Tunnel Tops & Landscape Architect James Corner Field Operations selected to develop the 14-acre parkland for San Francisco’s historic Presidio.
We poured all of the concrete on the project, including the decorative concrete and Shotcrete walls, and Central Concrete Supply Company was our Ready-Mix Concrete supplier who is an NRMCA member.
Evidence
We worked closely with Field Operations to develop all the site concrete including 4,400 CSF of the one-of-a-kind decorative shotcrete overlook walls, 139,250 SF of Lithocrete paving seeded with decorative aggregate ranging in size from ¾”, ¼”, and 1/8”, 10,600 CSF of walls with a light a quarried stone finish, 1,020 LF of stairs, 100 LF of stadium seats, 1,450 LF of curbs with a Titanium Dioxide admixture, and 8,500 SF all other site concrete.
The development process was very tedious because Field Operations and the Presidio Trust were very particular about the color palette of all the finishes and Central’s standard washed concrete sand was black and gave a “muddy” appearance no matter what integral color was selected.
To achieve their design intent, we worked with Central to import one of their light brown washed sand from a different region, and from there made numerous rounds of samples in different integral colors and modified the concrete matrix with cementitious replacement materials, including Flyash and Slag, in different percentages to shift the color hue until we achieved the perfect color that the team bought off on. We ended up with a blend of 50% Type 1L Cement and 50% Slag along with an integral color.
This project won two American Society of Concrete Contractors (ASCC) Decorative Concrete Council awards in 2023. 1st place for “Architectural Cast-in-place” & 2nd place in “Multiple Applications”.
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